Commit c2a779ae79

Jacob Young <jacobly0@users.noreply.github.com>
2024-11-01 01:55:34
std.crypto.tls: implement TLSv1.2
1 parent ee9f00d
Changed files (6)
lib/std/crypto/25519/ed25519.zig
@@ -151,7 +151,9 @@ pub const Ed25519 = struct {
         a: Curve,
         expected_r: Curve,
 
-        fn init(sig: Signature, public_key: PublicKey) (NonCanonicalError || EncodingError || IdentityElementError)!Verifier {
+        pub const InitError = NonCanonicalError || EncodingError || IdentityElementError;
+
+        fn init(sig: Signature, public_key: PublicKey) InitError!Verifier {
             const r = sig.r;
             const s = sig.s;
             try Curve.scalar.rejectNonCanonical(s);
@@ -173,8 +175,11 @@ pub const Ed25519 = struct {
             self.h.update(msg);
         }
 
+        pub const VerifyError = WeakPublicKeyError || IdentityElementError ||
+            SignatureVerificationError;
+
         /// Verify that the signature is valid for the entire message.
-        pub fn verify(self: *Verifier) (SignatureVerificationError || WeakPublicKeyError || IdentityElementError)!void {
+        pub fn verify(self: *Verifier) VerifyError!void {
             var hram64: [Sha512.digest_length]u8 = undefined;
             self.h.final(&hram64);
             const hram = Curve.scalar.reduce64(hram64);
@@ -197,10 +202,10 @@ pub const Ed25519 = struct {
         s: CompressedScalar,
 
         /// Return the raw signature (r, s) in little-endian format.
-        pub fn toBytes(self: Signature) [encoded_length]u8 {
+        pub fn toBytes(sig: Signature) [encoded_length]u8 {
             var bytes: [encoded_length]u8 = undefined;
-            bytes[0..Curve.encoded_length].* = self.r;
-            bytes[Curve.encoded_length..].* = self.s;
+            bytes[0..Curve.encoded_length].* = sig.r;
+            bytes[Curve.encoded_length..].* = sig.s;
             return bytes;
         }
 
@@ -214,17 +219,26 @@ pub const Ed25519 = struct {
         }
 
         /// Create a Verifier for incremental verification of a signature.
-        pub fn verifier(self: Signature, public_key: PublicKey) (NonCanonicalError || EncodingError || IdentityElementError)!Verifier {
-            return Verifier.init(self, public_key);
+        pub fn verifier(sig: Signature, public_key: PublicKey) Verifier.InitError!Verifier {
+            return Verifier.init(sig, public_key);
         }
 
+        pub const VerifyError = Verifier.InitError || Verifier.VerifyError;
+
         /// Verify the signature against a message and public key.
         /// Return IdentityElement or NonCanonical if the public key or signature are not in the expected range,
         /// or SignatureVerificationError if the signature is invalid for the given message and key.
-        pub fn verify(self: Signature, msg: []const u8, public_key: PublicKey) (IdentityElementError || NonCanonicalError || SignatureVerificationError || EncodingError || WeakPublicKeyError)!void {
-            var st = try Verifier.init(self, public_key);
-            st.update(msg);
-            return st.verify();
+        pub fn verify(sig: Signature, msg: []const u8, public_key: PublicKey) VerifyError!void {
+            try sig.concatVerify(&.{msg}, public_key);
+        }
+
+        /// Verify the signature against a concatenated message and public key.
+        /// Return IdentityElement or NonCanonical if the public key or signature are not in the expected range,
+        /// or SignatureVerificationError if the signature is invalid for the given message and key.
+        pub fn concatVerify(sig: Signature, msg: []const []const u8, public_key: PublicKey) VerifyError!void {
+            var st = try Verifier.init(sig, public_key);
+            for (msg) |part| st.update(part);
+            try st.verify();
         }
     };
 
lib/std/crypto/tls/Client.zig
@@ -8,12 +8,14 @@ const assert = std.debug.assert;
 const Certificate = std.crypto.Certificate;
 
 const max_ciphertext_len = tls.max_ciphertext_len;
+const hmacExpandLabel = tls.hmacExpandLabel;
 const hkdfExpandLabel = tls.hkdfExpandLabel;
 const int2 = tls.int2;
 const int3 = tls.int3;
 const array = tls.array;
 const enum_array = tls.enum_array;
 
+tls_version: tls.ProtocolVersion,
 read_seq: u64,
 write_seq: u64,
 /// The starting index of cleartext bytes inside `partially_read_buffer`.
@@ -136,7 +138,7 @@ pub fn InitError(comptime Stream: type) type {
     };
 }
 
-/// Initiates a TLS handshake and establishes a TLSv1.3 session with `stream`, which
+/// Initiates a TLS handshake and establishes a TLSv1.2 or TLSv1.3 session with `stream`, which
 /// must conform to `StreamInterface`.
 ///
 /// `host` is only borrowed during this function call.
@@ -145,26 +147,20 @@ pub fn init(stream: anytype, ca_bundle: Certificate.Bundle, host: []const u8) In
 
     var random_buffer: [128]u8 = undefined;
     crypto.random.bytes(&random_buffer);
-    const hello_rand = random_buffer[0..32].*;
+    const client_hello_rand = random_buffer[0..32].*;
+    var server_hello_rand: [32]u8 = undefined;
     const legacy_session_id = random_buffer[32..64].*;
-    const x25519_kp_seed = random_buffer[64..96].*;
-    const secp256r1_kp_seed = random_buffer[96..128].*;
 
-    const x25519_kp = crypto.dh.X25519.KeyPair.create(x25519_kp_seed) catch |err| switch (err) {
-        // Only possible to happen if the private key is all zeroes.
+    var key_share = KeyShare.init(random_buffer[64..128].*) catch |err| switch (err) {
+        // Only possible to happen if the seed is all zeroes.
         error.IdentityElement => return error.InsufficientEntropy,
     };
-    const secp256r1_kp = crypto.sign.ecdsa.EcdsaP256Sha256.KeyPair.create(secp256r1_kp_seed) catch |err| switch (err) {
-        // Only possible to happen if the private key is all zeroes.
-        error.IdentityElement => return error.InsufficientEntropy,
-    };
-    const ml_kem768_kp = crypto.kem.ml_kem.MLKem768.KeyPair.create(null) catch {};
 
     const extensions_payload =
-        tls.extension(.supported_versions, [_]u8{
-        0x02, // byte length of supported versions
-        0x03, 0x04, // TLS 1.3
-    }) ++ tls.extension(.signature_algorithms, enum_array(tls.SignatureScheme, &.{
+        tls.extension(.supported_versions, [_]u8{2 + 2} ++ // byte length of supported versions
+        int2(@intFromEnum(tls.ProtocolVersion.tls_1_3)) ++
+        int2(@intFromEnum(tls.ProtocolVersion.tls_1_2))) ++
+        tls.extension(.signature_algorithms, enum_array(tls.SignatureScheme, &.{
         .ecdsa_secp256r1_sha256,
         .ecdsa_secp384r1_sha384,
         .rsa_pss_rsae_sha256,
@@ -178,11 +174,11 @@ pub fn init(stream: anytype, ca_bundle: Certificate.Bundle, host: []const u8) In
     })) ++ tls.extension(
         .key_share,
         array(1, int2(@intFromEnum(tls.NamedGroup.x25519)) ++
-            array(1, x25519_kp.public_key) ++
+            array(1, key_share.x25519_kp.public_key) ++
             int2(@intFromEnum(tls.NamedGroup.secp256r1)) ++
-            array(1, secp256r1_kp.public_key.toUncompressedSec1()) ++
+            array(1, key_share.secp256r1_kp.public_key.toUncompressedSec1()) ++
             int2(@intFromEnum(tls.NamedGroup.x25519_ml_kem768)) ++
-            array(1, x25519_kp.public_key ++ ml_kem768_kp.public_key.toBytes())),
+            array(1, key_share.x25519_kp.public_key ++ key_share.ml_kem768_kp.public_key.toBytes())),
     ) ++
         int2(@intFromEnum(tls.ExtensionType.server_name)) ++
         int2(host_len + 5) ++ // byte length of this extension payload
@@ -198,7 +194,7 @@ pub fn init(stream: anytype, ca_bundle: Certificate.Bundle, host: []const u8) In
 
     const client_hello =
         int2(@intFromEnum(tls.ProtocolVersion.tls_1_2)) ++
-        hello_rand ++
+        client_hello_rand ++
         [1]u8{32} ++ legacy_session_id ++
         cipher_suites ++
         int2(legacy_compression_methods) ++
@@ -209,16 +205,16 @@ pub fn init(stream: anytype, ca_bundle: Certificate.Bundle, host: []const u8) In
         int3(@intCast(client_hello.len + host_len)) ++
         client_hello;
 
-    const plaintext_header = [_]u8{
-        @intFromEnum(tls.ContentType.handshake),
-        0x03, 0x01, // legacy_record_version
-    } ++ int2(@intCast(out_handshake.len + host_len)) ++ out_handshake;
+    const cleartext_header = [_]u8{@intFromEnum(tls.ContentType.handshake)} ++
+        int2(@intFromEnum(tls.ProtocolVersion.tls_1_0)) ++ // legacy_record_version
+        int2(@intCast(out_handshake.len + host_len)) ++
+        out_handshake;
 
     {
         var iovecs = [_]std.posix.iovec_const{
             .{
-                .base = &plaintext_header,
-                .len = plaintext_header.len,
+                .base = &cleartext_header,
+                .len = cleartext_header.len,
             },
             .{
                 .base = host.ptr,
@@ -228,8 +224,10 @@ pub fn init(stream: anytype, ca_bundle: Certificate.Bundle, host: []const u8) In
         try stream.writevAll(&iovecs);
     }
 
-    const client_hello_bytes1 = plaintext_header[5..];
+    const client_hello_bytes1 = cleartext_header[tls.record_header_len..];
 
+    var tls_version: tls.ProtocolVersion = undefined;
+    var cipher_suite_tag: tls.CipherSuite = undefined;
     var handshake_cipher: tls.HandshakeCipher = undefined;
     var handshake_buffer: [8000]u8 = undefined;
     var d: tls.Decoder = .{ .buf = &handshake_buffer };
@@ -259,10 +257,10 @@ pub fn init(stream: anytype, ca_bundle: Certificate.Bundle, host: []const u8) In
                 if (handshake_type != .server_hello) return error.TlsUnexpectedMessage;
                 const length = ptd.decode(u24);
                 var hsd = try ptd.sub(length);
-                try hsd.ensure(2 + 32 + 1 + 32 + 2 + 1 + 2);
+                try hsd.ensure(2 + 32 + 1 + 32 + 2 + 1);
                 const legacy_version = hsd.decode(u16);
-                const random = hsd.array(32);
-                if (mem.eql(u8, random, &tls.hello_retry_request_sequence)) {
+                @memcpy(&server_hello_rand, hsd.array(32));
+                if (mem.eql(u8, &server_hello_rand, &tls.hello_retry_request_sequence)) {
                     // This is a HelloRetryRequest message. This client implementation
                     // does not expect to get one.
                     return error.TlsUnexpectedMessage;
@@ -270,83 +268,44 @@ pub fn init(stream: anytype, ca_bundle: Certificate.Bundle, host: []const u8) In
                 const legacy_session_id_echo_len = hsd.decode(u8);
                 if (legacy_session_id_echo_len != 32) return error.TlsIllegalParameter;
                 const legacy_session_id_echo = hsd.array(32);
-                if (!mem.eql(u8, legacy_session_id_echo, &legacy_session_id))
-                    return error.TlsIllegalParameter;
-                const cipher_suite_tag = hsd.decode(tls.CipherSuite);
+                cipher_suite_tag = hsd.decode(tls.CipherSuite);
                 hsd.skip(1); // legacy_compression_method
-                const extensions_size = hsd.decode(u16);
-                var all_extd = try hsd.sub(extensions_size);
-                var supported_version: u16 = 0;
-                var shared_key: []const u8 = undefined;
-                var have_shared_key = false;
-                while (!all_extd.eof()) {
-                    try all_extd.ensure(2 + 2);
-                    const et = all_extd.decode(tls.ExtensionType);
-                    const ext_size = all_extd.decode(u16);
-                    var extd = try all_extd.sub(ext_size);
-                    switch (et) {
-                        .supported_versions => {
-                            if (supported_version != 0) return error.TlsIllegalParameter;
-                            try extd.ensure(2);
-                            supported_version = extd.decode(u16);
-                        },
-                        .key_share => {
-                            if (have_shared_key) return error.TlsIllegalParameter;
-                            have_shared_key = true;
-                            try extd.ensure(4);
-                            const named_group = extd.decode(tls.NamedGroup);
-                            const key_size = extd.decode(u16);
-                            try extd.ensure(key_size);
-                            switch (named_group) {
-                                .x25519_ml_kem768 => {
-                                    const xksl = crypto.dh.X25519.public_length;
-                                    const hksl = xksl + crypto.kem.ml_kem.MLKem768.ciphertext_length;
-                                    if (key_size != hksl)
-                                        return error.TlsIllegalParameter;
-                                    const server_ks = extd.array(hksl);
-
-                                    shared_key = &((crypto.dh.X25519.scalarmult(
-                                        x25519_kp.secret_key,
-                                        server_ks[0..xksl].*,
-                                    ) catch return error.TlsDecryptFailure) ++ (ml_kem768_kp.secret_key.decaps(
-                                        server_ks[xksl..hksl],
-                                    ) catch return error.TlsDecryptFailure));
-                                },
-                                .x25519 => {
-                                    const ksl = crypto.dh.X25519.public_length;
-                                    if (key_size != ksl) return error.TlsIllegalParameter;
-                                    const server_pub_key = extd.array(ksl);
-
-                                    shared_key = &(crypto.dh.X25519.scalarmult(
-                                        x25519_kp.secret_key,
-                                        server_pub_key.*,
-                                    ) catch return error.TlsDecryptFailure);
-                                },
-                                .secp256r1 => {
-                                    const server_pub_key = extd.slice(key_size);
-
-                                    const PublicKey = crypto.sign.ecdsa.EcdsaP256Sha256.PublicKey;
-                                    const pk = PublicKey.fromSec1(server_pub_key) catch {
-                                        return error.TlsDecryptFailure;
-                                    };
-                                    const mul = pk.p.mulPublic(secp256r1_kp.secret_key.bytes, .big) catch {
-                                        return error.TlsDecryptFailure;
-                                    };
-                                    shared_key = &mul.affineCoordinates().x.toBytes(.big);
-                                },
-                                else => {
-                                    return error.TlsIllegalParameter;
-                                },
-                            }
-                        },
-                        else => {},
+                var supported_version: ?u16 = null;
+                if (!hsd.eof()) {
+                    try hsd.ensure(2);
+                    const extensions_size = hsd.decode(u16);
+                    var all_extd = try hsd.sub(extensions_size);
+                    while (!all_extd.eof()) {
+                        try all_extd.ensure(2 + 2);
+                        const et = all_extd.decode(tls.ExtensionType);
+                        const ext_size = all_extd.decode(u16);
+                        var extd = try all_extd.sub(ext_size);
+                        switch (et) {
+                            .supported_versions => {
+                                if (supported_version) |_| return error.TlsIllegalParameter;
+                                try extd.ensure(2);
+                                supported_version = extd.decode(u16);
+                            },
+                            .key_share => {
+                                if (key_share.getSharedSecret()) |_| return error.TlsIllegalParameter;
+                                try extd.ensure(4);
+                                const named_group = extd.decode(tls.NamedGroup);
+                                const key_size = extd.decode(u16);
+                                try extd.ensure(key_size);
+                                try key_share.exchange(named_group, extd.slice(key_size));
+                            },
+                            else => {},
+                        }
                     }
                 }
-                if (!have_shared_key) return error.TlsIllegalParameter;
 
-                const tls_version = if (supported_version == 0) legacy_version else supported_version;
-                if (tls_version != @intFromEnum(tls.ProtocolVersion.tls_1_3))
-                    return error.TlsIllegalParameter;
+                tls_version = @enumFromInt(supported_version orelse legacy_version);
+                switch (tls_version) {
+                    .tls_1_3 => if (!mem.eql(u8, legacy_session_id_echo, &legacy_session_id)) return error.TlsIllegalParameter,
+                    .tls_1_2 => if (mem.eql(u8, server_hello_rand[24..31], "DOWNGRD") and
+                        server_hello_rand[31] >> 1 == 0x00) return error.TlsIllegalParameter,
+                    else => return error.TlsIllegalParameter,
+                }
 
                 switch (cipher_suite_tag) {
                     inline .AES_128_GCM_SHA256,
@@ -354,43 +313,63 @@ pub fn init(stream: anytype, ca_bundle: Certificate.Bundle, host: []const u8) In
                     .CHACHA20_POLY1305_SHA256,
                     .AEGIS_256_SHA512,
                     .AEGIS_128L_SHA256,
+
+                    .ECDHE_RSA_WITH_AES_128_GCM_SHA256,
+                    .ECDHE_RSA_WITH_AES_256_GCM_SHA384,
+                    .ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
                     => |tag| {
-                        const P = std.meta.TagPayloadByName(tls.HandshakeCipher, @tagName(tag));
-                        handshake_cipher = @unionInit(tls.HandshakeCipher, @tagName(tag), .{
-                            .handshake_secret = undefined,
-                            .master_secret = undefined,
-                            .client_handshake_key = undefined,
-                            .server_handshake_key = undefined,
-                            .client_finished_key = undefined,
-                            .server_finished_key = undefined,
-                            .client_handshake_iv = undefined,
-                            .server_handshake_iv = undefined,
-                            .transcript_hash = P.Hash.init(.{}),
+                        handshake_cipher = @unionInit(tls.HandshakeCipher, @tagName(tag.with()), .{
+                            .transcript_hash = .init(.{}),
+                            .version = undefined,
                         });
-                        const p = &@field(handshake_cipher, @tagName(tag));
+                        const p = &@field(handshake_cipher, @tagName(tag.with()));
                         p.transcript_hash.update(client_hello_bytes1); // Client Hello part 1
                         p.transcript_hash.update(host); // Client Hello part 2
                         p.transcript_hash.update(server_hello_fragment);
-                        const hello_hash = p.transcript_hash.peek();
-                        const zeroes = [1]u8{0} ** P.Hash.digest_length;
-                        const early_secret = P.Hkdf.extract(&[1]u8{0}, &zeroes);
-                        const empty_hash = tls.emptyHash(P.Hash);
-                        const hs_derived_secret = hkdfExpandLabel(P.Hkdf, early_secret, "derived", &empty_hash, P.Hash.digest_length);
-                        p.handshake_secret = P.Hkdf.extract(&hs_derived_secret, shared_key);
-                        const ap_derived_secret = hkdfExpandLabel(P.Hkdf, p.handshake_secret, "derived", &empty_hash, P.Hash.digest_length);
-                        p.master_secret = P.Hkdf.extract(&ap_derived_secret, &zeroes);
-                        const client_secret = hkdfExpandLabel(P.Hkdf, p.handshake_secret, "c hs traffic", &hello_hash, P.Hash.digest_length);
-                        const server_secret = hkdfExpandLabel(P.Hkdf, p.handshake_secret, "s hs traffic", &hello_hash, P.Hash.digest_length);
-                        p.client_finished_key = hkdfExpandLabel(P.Hkdf, client_secret, "finished", "", P.Hmac.key_length);
-                        p.server_finished_key = hkdfExpandLabel(P.Hkdf, server_secret, "finished", "", P.Hmac.key_length);
-                        p.client_handshake_key = hkdfExpandLabel(P.Hkdf, client_secret, "key", "", P.AEAD.key_length);
-                        p.server_handshake_key = hkdfExpandLabel(P.Hkdf, server_secret, "key", "", P.AEAD.key_length);
-                        p.client_handshake_iv = hkdfExpandLabel(P.Hkdf, client_secret, "iv", "", P.AEAD.nonce_length);
-                        p.server_handshake_iv = hkdfExpandLabel(P.Hkdf, server_secret, "iv", "", P.AEAD.nonce_length);
                     },
-                    else => {
-                        return error.TlsIllegalParameter;
+
+                    else => return error.TlsIllegalParameter,
+                }
+                switch (tls_version) {
+                    .tls_1_3 => switch (cipher_suite_tag) {
+                        inline .AES_128_GCM_SHA256,
+                        .AES_256_GCM_SHA384,
+                        .CHACHA20_POLY1305_SHA256,
+                        .AEGIS_256_SHA512,
+                        .AEGIS_128L_SHA256,
+                        => |tag| {
+                            const sk = key_share.getSharedSecret() orelse return error.TlsIllegalParameter;
+                            const p = &@field(handshake_cipher, @tagName(tag.with()));
+                            const P = @TypeOf(p.*).A;
+                            const hello_hash = p.transcript_hash.peek();
+                            const zeroes = [1]u8{0} ** P.Hash.digest_length;
+                            const early_secret = P.Hkdf.extract(&[1]u8{0}, &zeroes);
+                            const empty_hash = tls.emptyHash(P.Hash);
+                            p.version = .{ .tls_1_3 = undefined };
+                            const pv = &p.version.tls_1_3;
+                            const hs_derived_secret = hkdfExpandLabel(P.Hkdf, early_secret, "derived", &empty_hash, P.Hash.digest_length);
+                            pv.handshake_secret = P.Hkdf.extract(&hs_derived_secret, sk);
+                            const ap_derived_secret = hkdfExpandLabel(P.Hkdf, pv.handshake_secret, "derived", &empty_hash, P.Hash.digest_length);
+                            pv.master_secret = P.Hkdf.extract(&ap_derived_secret, &zeroes);
+                            const client_secret = hkdfExpandLabel(P.Hkdf, pv.handshake_secret, "c hs traffic", &hello_hash, P.Hash.digest_length);
+                            const server_secret = hkdfExpandLabel(P.Hkdf, pv.handshake_secret, "s hs traffic", &hello_hash, P.Hash.digest_length);
+                            pv.client_finished_key = hkdfExpandLabel(P.Hkdf, client_secret, "finished", "", P.Hmac.key_length);
+                            pv.server_finished_key = hkdfExpandLabel(P.Hkdf, server_secret, "finished", "", P.Hmac.key_length);
+                            pv.client_handshake_key = hkdfExpandLabel(P.Hkdf, client_secret, "key", "", P.AEAD.key_length);
+                            pv.server_handshake_key = hkdfExpandLabel(P.Hkdf, server_secret, "key", "", P.AEAD.key_length);
+                            pv.client_handshake_iv = hkdfExpandLabel(P.Hkdf, client_secret, "iv", "", P.AEAD.nonce_length);
+                            pv.server_handshake_iv = hkdfExpandLabel(P.Hkdf, server_secret, "iv", "", P.AEAD.nonce_length);
+                        },
+                        else => return error.TlsIllegalParameter,
+                    },
+                    .tls_1_2 => switch (cipher_suite_tag) {
+                        .ECDHE_RSA_WITH_AES_128_GCM_SHA256,
+                        .ECDHE_RSA_WITH_AES_256_GCM_SHA384,
+                        .ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
+                        => {},
+                        else => return error.TlsIllegalParameter,
                     },
+                    else => return error.TlsIllegalParameter,
                 }
             },
             else => return error.TlsUnexpectedMessage,
@@ -404,58 +383,74 @@ pub fn init(stream: anytype, ca_bundle: Certificate.Bundle, host: []const u8) In
     //   the previous certificate in memory so that it can be verified by the
     //   next one.
     var cert_index: usize = 0;
+    var write_seq: u64 = 0;
     var read_seq: u64 = 0;
     var prev_cert: Certificate.Parsed = undefined;
-    // Set to true once a trust chain has been established from the first
-    // certificate to a root CA.
+    const CipherState = enum {
+        /// No cipher is in use
+        cleartext,
+        /// Handshake cipher is in use
+        handshake,
+        /// Application cipher is in use
+        application,
+    };
+    var pending_cipher_state: CipherState = switch (tls_version) {
+        .tls_1_3 => .handshake,
+        .tls_1_2 => .cleartext,
+        else => unreachable,
+    };
+    var cipher_state: CipherState = .cleartext;
     const HandshakeState = enum {
         /// In this state we expect only an encrypted_extensions message.
         encrypted_extensions,
-        /// In this state we expect certificate messages.
+        /// In this state we expect certificate handshake messages.
         certificate,
         /// In this state we expect certificate or certificate_verify messages.
         /// certificate messages are ignored since the trust chain is already
         /// established.
         trust_chain_established,
-        /// In this state, we expect only the finished message.
+        /// In this state, we expect only the server_hello_done handshake message.
+        server_hello_done,
+        /// In this state, we expect only the finished handshake message.
         finished,
     };
-    var handshake_state: HandshakeState = .encrypted_extensions;
+    var handshake_state: HandshakeState = switch (tls_version) {
+        .tls_1_3 => .encrypted_extensions,
+        .tls_1_2 => .certificate,
+        else => unreachable,
+    };
     var cleartext_bufs: [2][8000]u8 = undefined;
-    var main_cert_pub_key_algo: Certificate.AlgorithmCategory = undefined;
-    var main_cert_pub_key_buf: [600]u8 = undefined;
-    var main_cert_pub_key_len: u16 = undefined;
+    var main_cert_pub_key: CertificatePublicKey = undefined;
     const now_sec = std.time.timestamp();
 
     while (true) {
         try d.readAtLeastOurAmt(stream, tls.record_header_len);
-        const record_header = d.buf[d.idx..][0..5];
-        const ct = d.decode(tls.ContentType);
+        const record_header = d.buf[d.idx..][0..tls.record_header_len];
+        const record_ct = d.decode(tls.ContentType);
         d.skip(2); // legacy_version
         const record_len = d.decode(u16);
         try d.readAtLeast(stream, record_len);
         var record_decoder = try d.sub(record_len);
-        switch (ct) {
-            .change_cipher_spec => {
-                try record_decoder.ensure(1);
-                if (record_decoder.decode(u8) != 0x01) return error.TlsIllegalParameter;
-            },
-            .application_data => {
+        var ctd, const ct = content: switch (cipher_state) {
+            .cleartext => .{ record_decoder, record_ct },
+            .handshake => {
+                std.debug.assert(tls_version == .tls_1_3);
+                if (record_ct != .application_data) return error.TlsUnexpectedMessage;
+                try record_decoder.ensure(record_len);
                 const cleartext_buf = &cleartext_bufs[cert_index % 2];
-
-                const cleartext = switch (handshake_cipher) {
-                    inline else => |*p| c: {
-                        const P = @TypeOf(p.*);
-                        const ciphertext_len = record_len - P.AEAD.tag_length;
-                        try record_decoder.ensure(ciphertext_len + P.AEAD.tag_length);
-                        const ciphertext = record_decoder.slice(ciphertext_len);
+                const cleartext = cleartext: switch (handshake_cipher) {
+                    inline else => |*p| {
+                        const pv = &p.version.tls_1_3;
+                        const P = @TypeOf(p.*).A;
+                        if (record_len < P.AEAD.tag_length) return error.TlsRecordOverflow;
+                        const ciphertext = record_decoder.slice(record_len - P.AEAD.tag_length);
                         if (ciphertext.len > cleartext_buf.len) return error.TlsRecordOverflow;
                         const cleartext = cleartext_buf[0..ciphertext.len];
                         const auth_tag = record_decoder.array(P.AEAD.tag_length).*;
                         const nonce = if (builtin.zig_backend == .stage2_x86_64 and
                             P.AEAD.nonce_length > comptime std.simd.suggestVectorLength(u8) orelse 1)
                         nonce: {
-                            var nonce = p.server_handshake_iv;
+                            var nonce = pv.server_handshake_iv;
                             const operand = std.mem.readInt(u64, nonce[nonce.len - 8 ..], .big);
                             std.mem.writeInt(u64, nonce[nonce.len - 8 ..], operand ^ read_seq, .big);
                             break :nonce nonce;
@@ -463,200 +458,320 @@ pub fn init(stream: anytype, ca_bundle: Certificate.Bundle, host: []const u8) In
                             const V = @Vector(P.AEAD.nonce_length, u8);
                             const pad = [1]u8{0} ** (P.AEAD.nonce_length - 8);
                             const operand: V = pad ++ @as([8]u8, @bitCast(big(read_seq)));
-                            break :nonce @as(V, p.server_handshake_iv) ^ operand;
+                            break :nonce @as(V, pv.server_handshake_iv) ^ operand;
                         };
-                        read_seq += 1;
-                        P.AEAD.decrypt(cleartext, ciphertext, auth_tag, record_header, nonce, p.server_handshake_key) catch
+                        P.AEAD.decrypt(cleartext, ciphertext, auth_tag, record_header, nonce, pv.server_handshake_key) catch
                             return error.TlsBadRecordMac;
-                        break :c @constCast(mem.trimRight(u8, cleartext, "\x00"));
+                        break :cleartext mem.trimRight(u8, cleartext, "\x00");
                     },
                 };
+                read_seq += 1;
+                const ct: tls.ContentType = @enumFromInt(cleartext[cleartext.len - 1]);
+                if (ct != .handshake) return error.TlsUnexpectedMessage;
+                break :content .{ tls.Decoder.fromTheirSlice(@constCast(cleartext[0 .. cleartext.len - 1])), ct };
+            },
+            .application => {
+                std.debug.assert(tls_version == .tls_1_2);
+                if (record_ct != .handshake) return error.TlsUnexpectedMessage;
+                try record_decoder.ensure(record_len);
+                const cleartext_buf = &cleartext_bufs[cert_index % 2];
+                const cleartext = cleartext: switch (handshake_cipher) {
+                    inline else => |*p| {
+                        const pv = &p.version.tls_1_2;
+                        const P = @TypeOf(p.*).A;
+                        if (record_len < P.record_iv_length + P.mac_length) return error.TlsRecordOverflow;
+                        const message_len: u16 = record_len - P.record_iv_length - P.mac_length;
+                        if (message_len > cleartext_buf.len) return error.TlsRecordOverflow;
+                        const cleartext = cleartext_buf[0..message_len];
+                        const ad = std.mem.toBytes(big(read_seq)) ++
+                            record_header[0 .. 1 + 2] ++
+                            std.mem.toBytes(big(message_len));
+                        const record_iv = record_decoder.array(P.record_iv_length).*;
+                        const masked_read_seq = read_seq &
+                            comptime std.math.shl(u64, std.math.maxInt(u64), 8 * P.record_iv_length);
+                        const nonce: [P.AEAD.nonce_length]u8 = if (builtin.zig_backend == .stage2_x86_64 and
+                            P.AEAD.nonce_length > comptime std.simd.suggestVectorLength(u8) orelse 1)
+                        nonce: {
+                            var nonce = pv.app_cipher.server_write_IV ++ record_iv;
+                            const operand = std.mem.readInt(u64, nonce[nonce.len - 8 ..], .big);
+                            std.mem.writeInt(u64, nonce[nonce.len - 8 ..], operand ^ masked_read_seq, .big);
+                            break :nonce nonce;
+                        } else nonce: {
+                            const V = @Vector(P.AEAD.nonce_length, u8);
+                            const pad = [1]u8{0} ** (P.AEAD.nonce_length - 8);
+                            const operand: V = pad ++ @as([8]u8, @bitCast(big(masked_read_seq)));
+                            break :nonce @as(V, pv.app_cipher.server_write_IV ++ record_iv) ^ operand;
+                        };
+                        const ciphertext = record_decoder.slice(message_len);
+                        const auth_tag = record_decoder.array(P.mac_length);
+                        P.AEAD.decrypt(cleartext, ciphertext, auth_tag.*, ad, nonce, pv.app_cipher.server_write_key) catch return error.TlsBadRecordMac;
+                        break :cleartext cleartext;
+                    },
+                };
+                read_seq += 1;
+                break :content .{ tls.Decoder.fromTheirSlice(cleartext), record_ct };
+            },
+        };
+        switch (ct) {
+            .alert => {
+                try ctd.ensure(2);
+                const level = ctd.decode(tls.AlertLevel);
+                const desc = ctd.decode(tls.AlertDescription);
+                _ = level;
 
-                const inner_ct: tls.ContentType = @enumFromInt(cleartext[cleartext.len - 1]);
-                if (inner_ct != .handshake) return error.TlsUnexpectedMessage;
-
-                var ctd = tls.Decoder.fromTheirSlice(cleartext[0 .. cleartext.len - 1]);
-                while (true) {
-                    try ctd.ensure(4);
-                    const handshake_type = ctd.decode(tls.HandshakeType);
-                    const handshake_len = ctd.decode(u24);
-                    var hsd = try ctd.sub(handshake_len);
-                    const wrapped_handshake = ctd.buf[ctd.idx - handshake_len - 4 .. ctd.idx];
-                    const handshake = ctd.buf[ctd.idx - handshake_len .. ctd.idx];
-                    switch (handshake_type) {
-                        .encrypted_extensions => {
-                            if (handshake_state != .encrypted_extensions) return error.TlsUnexpectedMessage;
-                            handshake_state = .certificate;
-                            switch (handshake_cipher) {
-                                inline else => |*p| p.transcript_hash.update(wrapped_handshake),
-                            }
-                            try hsd.ensure(2);
-                            const total_ext_size = hsd.decode(u16);
-                            var all_extd = try hsd.sub(total_ext_size);
-                            while (!all_extd.eof()) {
-                                try all_extd.ensure(4);
-                                const et = all_extd.decode(tls.ExtensionType);
-                                const ext_size = all_extd.decode(u16);
-                                const extd = try all_extd.sub(ext_size);
-                                _ = extd;
-                                switch (et) {
-                                    .server_name => {},
-                                    else => {},
-                                }
+                // if this isn't a error alert, then it's a closure alert, which makes no sense in a handshake
+                try desc.toError();
+                // TODO: handle server-side closures
+                return error.TlsUnexpectedMessage;
+            },
+            .change_cipher_spec => {
+                try ctd.ensure(1);
+                if (ctd.decode(u8) != 0x01) return error.TlsIllegalParameter;
+                cipher_state = pending_cipher_state;
+            },
+            .handshake => while (true) {
+                try ctd.ensure(4);
+                const handshake_type = ctd.decode(tls.HandshakeType);
+                const handshake_len = ctd.decode(u24);
+                var hsd = try ctd.sub(handshake_len);
+                const wrapped_handshake = ctd.buf[ctd.idx - handshake_len - 4 .. ctd.idx];
+                switch (handshake_type) {
+                    .encrypted_extensions => {
+                        if (tls_version != .tls_1_3) return error.TlsUnexpectedMessage;
+                        if (cipher_state != .handshake) return error.TlsUnexpectedMessage;
+                        if (handshake_state != .encrypted_extensions) return error.TlsUnexpectedMessage;
+                        handshake_state = .certificate;
+                        switch (handshake_cipher) {
+                            inline else => |*p| p.transcript_hash.update(wrapped_handshake),
+                        }
+                        try hsd.ensure(2);
+                        const total_ext_size = hsd.decode(u16);
+                        var all_extd = try hsd.sub(total_ext_size);
+                        while (!all_extd.eof()) {
+                            try all_extd.ensure(4);
+                            const et = all_extd.decode(tls.ExtensionType);
+                            const ext_size = all_extd.decode(u16);
+                            const extd = try all_extd.sub(ext_size);
+                            _ = extd;
+                            switch (et) {
+                                .server_name => {},
+                                else => {},
                             }
-                        },
-                        .certificate => cert: {
-                            switch (handshake_cipher) {
-                                inline else => |*p| p.transcript_hash.update(wrapped_handshake),
+                        }
+                    },
+                    .certificate => cert: {
+                        switch (handshake_cipher) {
+                            inline else => |*p| p.transcript_hash.update(wrapped_handshake),
+                        }
+                        switch (handshake_state) {
+                            .certificate => {},
+                            .trust_chain_established => break :cert,
+                            else => return error.TlsUnexpectedMessage,
+                        }
+
+                        switch (tls_version) {
+                            .tls_1_3 => {
+                                try hsd.ensure(1 + 3);
+                                const cert_req_ctx_len = hsd.decode(u8);
+                                if (cert_req_ctx_len != 0) return error.TlsIllegalParameter;
+                            },
+                            .tls_1_2 => try hsd.ensure(3),
+                            else => unreachable,
+                        }
+                        const certs_size = hsd.decode(u24);
+                        var certs_decoder = try hsd.sub(certs_size);
+                        while (!certs_decoder.eof()) {
+                            try certs_decoder.ensure(3);
+                            const cert_size = certs_decoder.decode(u24);
+                            const certd = try certs_decoder.sub(cert_size);
+
+                            const subject_cert: Certificate = .{
+                                .buffer = certd.buf,
+                                .index = @intCast(certd.idx),
+                            };
+                            const subject = try subject_cert.parse();
+                            if (cert_index == 0) {
+                                // Verify the host on the first certificate.
+                                try subject.verifyHostName(host);
+
+                                // Keep track of the public key for the
+                                // certificate_verify message later.
+                                try main_cert_pub_key.init(subject.pub_key_algo, subject.pubKey());
+                            } else {
+                                try prev_cert.verify(subject, now_sec);
                             }
-                            switch (handshake_state) {
-                                .certificate => {},
-                                .trust_chain_established => break :cert,
-                                else => return error.TlsUnexpectedMessage,
+
+                            if (ca_bundle.verify(subject, now_sec)) |_| {
+                                handshake_state = .trust_chain_established;
+                                break :cert;
+                            } else |err| switch (err) {
+                                error.CertificateIssuerNotFound => {},
+                                else => |e| return e,
                             }
-                            try hsd.ensure(1 + 4);
-                            const cert_req_ctx_len = hsd.decode(u8);
-                            if (cert_req_ctx_len != 0) return error.TlsIllegalParameter;
-                            const certs_size = hsd.decode(u24);
-                            var certs_decoder = try hsd.sub(certs_size);
-                            while (!certs_decoder.eof()) {
-                                try certs_decoder.ensure(3);
-                                const cert_size = certs_decoder.decode(u24);
-                                const certd = try certs_decoder.sub(cert_size);
-
-                                const subject_cert: Certificate = .{
-                                    .buffer = certd.buf,
-                                    .index = @intCast(certd.idx),
-                                };
-                                const subject = try subject_cert.parse();
-                                if (cert_index == 0) {
-                                    // Verify the host on the first certificate.
-                                    try subject.verifyHostName(host);
-
-                                    // Keep track of the public key for the
-                                    // certificate_verify message later.
-                                    main_cert_pub_key_algo = subject.pub_key_algo;
-                                    const pub_key = subject.pubKey();
-                                    if (pub_key.len > main_cert_pub_key_buf.len)
-                                        return error.CertificatePublicKeyInvalid;
-                                    @memcpy(main_cert_pub_key_buf[0..pub_key.len], pub_key);
-                                    main_cert_pub_key_len = @intCast(pub_key.len);
-                                } else {
-                                    try prev_cert.verify(subject, now_sec);
-                                }
-
-                                if (ca_bundle.verify(subject, now_sec)) |_| {
-                                    handshake_state = .trust_chain_established;
-                                    break :cert;
-                                } else |err| switch (err) {
-                                    error.CertificateIssuerNotFound => {},
-                                    else => |e| return e,
-                                }
-
-                                prev_cert = subject;
-                                cert_index += 1;
 
+                            prev_cert = subject;
+                            cert_index += 1;
+
+                            if (tls_version == .tls_1_3) {
                                 try certs_decoder.ensure(2);
                                 const total_ext_size = certs_decoder.decode(u16);
                                 const all_extd = try certs_decoder.sub(total_ext_size);
                                 _ = all_extd;
                             }
-                        },
-                        .certificate_verify => {
-                            switch (handshake_state) {
-                                .trust_chain_established => handshake_state = .finished,
-                                .certificate => return error.TlsCertificateNotVerified,
-                                else => return error.TlsUnexpectedMessage,
-                            }
+                        }
+                    },
+                    .server_key_exchange => {
+                        if (tls_version != .tls_1_2) return error.TlsUnexpectedMessage;
+                        if (cipher_state != .cleartext) return error.TlsUnexpectedMessage;
+                        switch (handshake_state) {
+                            .trust_chain_established => handshake_state = .server_hello_done,
+                            .certificate => return error.TlsCertificateNotVerified,
+                            else => return error.TlsUnexpectedMessage,
+                        }
 
-                            try hsd.ensure(4);
-                            const scheme = hsd.decode(tls.SignatureScheme);
-                            const sig_len = hsd.decode(u16);
-                            try hsd.ensure(sig_len);
-                            const encoded_sig = hsd.slice(sig_len);
-                            const max_digest_len = 64;
-                            var verify_buffer: [64 + 34 + max_digest_len]u8 =
-                                ([1]u8{0x20} ** 64) ++
-                                "TLS 1.3, server CertificateVerify\x00".* ++
-                                @as([max_digest_len]u8, undefined);
-
-                            const verify_bytes = switch (handshake_cipher) {
-                                inline else => |*p| v: {
-                                    const transcript_digest = p.transcript_hash.peek();
-                                    verify_buffer[verify_buffer.len - max_digest_len ..][0..transcript_digest.len].* = transcript_digest;
-                                    p.transcript_hash.update(wrapped_handshake);
-                                    break :v verify_buffer[0 .. verify_buffer.len - max_digest_len + transcript_digest.len];
-                                },
-                            };
-                            const main_cert_pub_key = main_cert_pub_key_buf[0..main_cert_pub_key_len];
-
-                            switch (scheme) {
-                                inline .ecdsa_secp256r1_sha256,
-                                .ecdsa_secp384r1_sha384,
-                                => |comptime_scheme| {
-                                    if (main_cert_pub_key_algo != .X9_62_id_ecPublicKey)
-                                        return error.TlsBadSignatureScheme;
-                                    const Ecdsa = SchemeEcdsa(comptime_scheme);
-                                    const sig = try Ecdsa.Signature.fromDer(encoded_sig);
-                                    const key = try Ecdsa.PublicKey.fromSec1(main_cert_pub_key);
-                                    try sig.verify(verify_bytes, key);
-                                },
-                                inline .rsa_pss_rsae_sha256,
-                                .rsa_pss_rsae_sha384,
-                                .rsa_pss_rsae_sha512,
-                                => |comptime_scheme| {
-                                    if (main_cert_pub_key_algo != .rsaEncryption)
-                                        return error.TlsBadSignatureScheme;
-
-                                    const Hash = SchemeHash(comptime_scheme);
-                                    const rsa = Certificate.rsa;
-                                    const components = try rsa.PublicKey.parseDer(main_cert_pub_key);
-                                    const exponent = components.exponent;
-                                    const modulus = components.modulus;
-                                    switch (modulus.len) {
-                                        inline 128, 256, 512 => |modulus_len| {
-                                            const key = try rsa.PublicKey.fromBytes(exponent, modulus);
-                                            const sig = rsa.PSSSignature.fromBytes(modulus_len, encoded_sig);
-                                            try rsa.PSSSignature.verify(modulus_len, sig, verify_bytes, key, Hash);
-                                        },
-                                        else => {
-                                            return error.TlsBadRsaSignatureBitCount;
-                                        },
-                                    }
-                                },
-                                inline .ed25519 => |comptime_scheme| {
-                                    if (main_cert_pub_key_algo != .curveEd25519) return error.TlsBadSignatureScheme;
-                                    const Eddsa = SchemeEddsa(comptime_scheme);
-                                    if (encoded_sig.len != Eddsa.Signature.encoded_length) return error.InvalidEncoding;
-                                    const sig = Eddsa.Signature.fromBytes(encoded_sig[0..Eddsa.Signature.encoded_length].*);
-                                    if (main_cert_pub_key.len != Eddsa.PublicKey.encoded_length) return error.InvalidEncoding;
-                                    const key = try Eddsa.PublicKey.fromBytes(main_cert_pub_key[0..Eddsa.PublicKey.encoded_length].*);
-                                    try sig.verify(verify_bytes, key);
-                                },
-                                else => {
-                                    return error.TlsBadSignatureScheme;
-                                },
-                            }
-                        },
-                        .finished => {
-                            if (handshake_state != .finished) return error.TlsUnexpectedMessage;
-                            // This message is to trick buggy proxies into behaving correctly.
-                            const client_change_cipher_spec_msg = [_]u8{
-                                @intFromEnum(tls.ContentType.change_cipher_spec),
-                                0x03, 0x03, // legacy protocol version
-                                0x00, 0x01, // length
-                                0x01,
-                            };
-                            const app_cipher = switch (handshake_cipher) {
-                                inline else => |*p, tag| c: {
-                                    const P = @TypeOf(p.*);
+                        switch (handshake_cipher) {
+                            inline else => |*p| p.transcript_hash.update(wrapped_handshake),
+                        }
+                        try hsd.ensure(1 + 2 + 1);
+                        const curve_type = hsd.decode(u8);
+                        if (curve_type != 0x03) return error.TlsIllegalParameter; // named_curve
+                        const named_group = hsd.decode(tls.NamedGroup);
+                        if (named_group != .secp256r1) return error.TlsIllegalParameter;
+                        const key_size = hsd.decode(u8);
+                        try hsd.ensure(key_size);
+                        const server_pub_key = hsd.slice(key_size);
+                        try main_cert_pub_key.verifySignature(&hsd, &.{ &client_hello_rand, &server_hello_rand, hsd.buf[0..hsd.idx] });
+                        try key_share.exchange(named_group, server_pub_key);
+                    },
+                    .server_hello_done => {
+                        if (tls_version != .tls_1_2) return error.TlsUnexpectedMessage;
+                        if (cipher_state != .cleartext) return error.TlsUnexpectedMessage;
+                        if (handshake_state != .server_hello_done) return error.TlsUnexpectedMessage;
+                        handshake_state = .finished;
+
+                        const client_key_exchange_msg =
+                            [_]u8{@intFromEnum(tls.ContentType.handshake)} ++ // record content type
+                            int2(@intFromEnum(tls.ProtocolVersion.tls_1_2)) ++ // legacy protocol version
+                            int2(0x46) ++ // record length
+                            .{@intFromEnum(tls.HandshakeType.client_key_exchange)} ++ // handshake type
+                            int3(0x42) ++ // params length
+                            .{0x41} ++ // pubkey length
+                            key_share.secp256r1_kp.public_key.toUncompressedSec1();
+                        // This message is to trick buggy proxies into behaving correctly.
+                        const client_change_cipher_spec_msg =
+                            [_]u8{@intFromEnum(tls.ContentType.change_cipher_spec)} ++ // record content type
+                            int2(@intFromEnum(tls.ProtocolVersion.tls_1_2)) ++ // legacy protocol version
+                            int2(1) ++ // record length
+                            .{0x01};
+                        const pre_master_secret = key_share.getSharedSecret().?;
+                        switch (handshake_cipher) {
+                            inline else => |*p| {
+                                const P = @TypeOf(p.*).A;
+                                p.transcript_hash.update(wrapped_handshake);
+                                p.transcript_hash.update(client_key_exchange_msg[tls.record_header_len..]);
+                                const master_secret = hmacExpandLabel(P.Hmac, pre_master_secret, &.{
+                                    "master secret",
+                                    &client_hello_rand,
+                                    &server_hello_rand,
+                                }, 48);
+                                const key_block = hmacExpandLabel(
+                                    P.Hmac,
+                                    &master_secret,
+                                    &.{ "key expansion", &server_hello_rand, &client_hello_rand },
+                                    @sizeOf(P.Tls_1_2),
+                                );
+                                const verify_data_len = 12;
+                                const client_verify_cleartext =
+                                    [_]u8{@intFromEnum(tls.HandshakeType.finished)} ++ // handshake type
+                                    int3(verify_data_len) ++ // verify data length
+                                    hmacExpandLabel(P.Hmac, &master_secret, &.{ "client finished", &p.transcript_hash.peek() }, verify_data_len);
+                                p.transcript_hash.update(&client_verify_cleartext);
+                                p.version = .{ .tls_1_2 = .{
+                                    .server_verify_data = hmacExpandLabel(
+                                        P.Hmac,
+                                        &master_secret,
+                                        &.{ "server finished", &p.transcript_hash.finalResult() },
+                                        verify_data_len,
+                                    ),
+                                    .app_cipher = std.mem.bytesToValue(P.Tls_1_2, &key_block),
+                                } };
+                                const pv = &p.version.tls_1_2;
+                                pending_cipher_state = .application;
+                                const nonce: [P.AEAD.nonce_length]u8 = if (builtin.zig_backend == .stage2_x86_64 and
+                                    P.AEAD.nonce_length > comptime std.simd.suggestVectorLength(u8) orelse 1)
+                                nonce: {
+                                    var nonce = pv.app_cipher.client_write_IV ++ pv.app_cipher.client_salt;
+                                    const operand = std.mem.readInt(u64, nonce[nonce.len - 8 ..], .big);
+                                    std.mem.writeInt(u64, nonce[nonce.len - 8 ..], operand ^ write_seq, .big);
+                                    break :nonce nonce;
+                                } else nonce: {
+                                    const V = @Vector(P.AEAD.nonce_length, u8);
+                                    const pad = [1]u8{0} ** (P.AEAD.nonce_length - 8);
+                                    const operand: V = pad ++ @as([8]u8, @bitCast(big(write_seq)));
+                                    break :nonce @as(V, pv.app_cipher.client_write_IV ++ pv.app_cipher.client_salt) ^ operand;
+                                };
+                                var client_verify_msg = [_]u8{@intFromEnum(tls.ContentType.handshake)} ++ // record content type
+                                    int2(@intFromEnum(tls.ProtocolVersion.tls_1_2)) ++ // legacy protocol version
+                                    int2(P.record_iv_length + client_verify_cleartext.len + P.mac_length) ++ // record length
+                                    nonce[P.fixed_iv_length..].* ++
+                                    @as([client_verify_cleartext.len + P.mac_length]u8, undefined);
+                                P.AEAD.encrypt(
+                                    client_verify_msg[client_verify_msg.len - P.mac_length -
+                                        client_verify_cleartext.len ..][0..client_verify_cleartext.len],
+                                    client_verify_msg[client_verify_msg.len - P.mac_length ..][0..P.mac_length],
+                                    &client_verify_cleartext,
+                                    std.mem.toBytes(big(write_seq)) ++ client_verify_msg[0 .. 1 + 2] ++ int2(client_verify_cleartext.len),
+                                    nonce,
+                                    pv.app_cipher.client_write_key,
+                                );
+                                const all_msgs = client_key_exchange_msg ++ client_change_cipher_spec_msg ++ client_verify_msg;
+                                var all_msgs_vec = [_]std.posix.iovec_const{.{
+                                    .base = &all_msgs,
+                                    .len = all_msgs.len,
+                                }};
+                                try stream.writevAll(&all_msgs_vec);
+                            },
+                        }
+                        write_seq += 1;
+                    },
+                    .certificate_verify => {
+                        if (tls_version != .tls_1_3) return error.TlsUnexpectedMessage;
+                        if (cipher_state != .handshake) return error.TlsUnexpectedMessage;
+                        switch (handshake_state) {
+                            .trust_chain_established => handshake_state = .finished,
+                            .certificate => return error.TlsCertificateNotVerified,
+                            else => return error.TlsUnexpectedMessage,
+                        }
+                        switch (handshake_cipher) {
+                            inline else => |*p| {
+                                try main_cert_pub_key.verifySignature(&hsd, &.{
+                                    " " ** 64 ++ "TLS 1.3, server CertificateVerify\x00",
+                                    &p.transcript_hash.peek(),
+                                });
+                                p.transcript_hash.update(wrapped_handshake);
+                            },
+                        }
+                    },
+                    .finished => {
+                        if (cipher_state == .cleartext) return error.TlsUnexpectedMessage;
+                        if (handshake_state != .finished) return error.TlsUnexpectedMessage;
+                        // This message is to trick buggy proxies into behaving correctly.
+                        const client_change_cipher_spec_msg =
+                            [_]u8{@intFromEnum(tls.ContentType.change_cipher_spec)} ++
+                            int2(@intFromEnum(tls.ProtocolVersion.tls_1_2)) ++ // legacy protocol version
+                            int2(1) ++ // length
+                            .{0x01};
+                        const app_cipher = app_cipher: switch (handshake_cipher) {
+                            inline else => |*p, tag| switch (tls_version) {
+                                .tls_1_3 => {
+                                    const pv = &p.version.tls_1_3;
+                                    const P = @TypeOf(p.*).A;
                                     const finished_digest = p.transcript_hash.peek();
                                     p.transcript_hash.update(wrapped_handshake);
-                                    const expected_server_verify_data = tls.hmac(P.Hmac, &finished_digest, p.server_finished_key);
-                                    if (!mem.eql(u8, &expected_server_verify_data, handshake))
-                                        return error.TlsDecryptError;
+                                    const expected_server_verify_data = tls.hmac(P.Hmac, &finished_digest, pv.server_finished_key);
+                                    if (!mem.eql(u8, &expected_server_verify_data, hsd.buf)) return error.TlsDecryptError;
                                     const handshake_hash = p.transcript_hash.finalResult();
-                                    const verify_data = tls.hmac(P.Hmac, &handshake_hash, p.client_finished_key);
+                                    const verify_data = tls.hmac(P.Hmac, &handshake_hash, pv.client_finished_key);
                                     const out_cleartext = [_]u8{
                                         @intFromEnum(tls.HandshakeType.finished),
                                         0, 0, verify_data.len, // length
@@ -664,67 +779,78 @@ pub fn init(stream: anytype, ca_bundle: Certificate.Bundle, host: []const u8) In
 
                                     const wrapped_len = out_cleartext.len + P.AEAD.tag_length;
 
-                                    var finished_msg = [_]u8{
-                                        @intFromEnum(tls.ContentType.application_data),
-                                        0x03, 0x03, // legacy protocol version
-                                        0, wrapped_len, // byte length of encrypted record
-                                    } ++ @as([wrapped_len]u8, undefined);
+                                    var finished_msg = [_]u8{@intFromEnum(tls.ContentType.application_data)} ++
+                                        int2(@intFromEnum(tls.ProtocolVersion.tls_1_2)) ++ // legacy protocol version
+                                        int2(wrapped_len) ++ // byte length of encrypted record
+                                        @as([wrapped_len]u8, undefined);
 
-                                    const ad = finished_msg[0..5];
-                                    const ciphertext = finished_msg[5..][0..out_cleartext.len];
+                                    const ad = finished_msg[0..tls.record_header_len];
+                                    const ciphertext = finished_msg[tls.record_header_len..][0..out_cleartext.len];
                                     const auth_tag = finished_msg[finished_msg.len - P.AEAD.tag_length ..];
-                                    const nonce = p.client_handshake_iv;
-                                    P.AEAD.encrypt(ciphertext, auth_tag, &out_cleartext, ad, nonce, p.client_handshake_key);
+                                    const nonce = pv.client_handshake_iv;
+                                    P.AEAD.encrypt(ciphertext, auth_tag, &out_cleartext, ad, nonce, pv.client_handshake_key);
 
-                                    const both_msgs = client_change_cipher_spec_msg ++ finished_msg;
-                                    var both_msgs_vec = [_]std.posix.iovec_const{.{
-                                        .base = &both_msgs,
-                                        .len = both_msgs.len,
+                                    const all_msgs = client_change_cipher_spec_msg ++ finished_msg;
+                                    var all_msgs_vec = [_]std.posix.iovec_const{.{
+                                        .base = &all_msgs,
+                                        .len = all_msgs.len,
                                     }};
-                                    try stream.writevAll(&both_msgs_vec);
+                                    try stream.writevAll(&all_msgs_vec);
 
-                                    const client_secret = hkdfExpandLabel(P.Hkdf, p.master_secret, "c ap traffic", &handshake_hash, P.Hash.digest_length);
-                                    const server_secret = hkdfExpandLabel(P.Hkdf, p.master_secret, "s ap traffic", &handshake_hash, P.Hash.digest_length);
-                                    break :c @unionInit(tls.ApplicationCipher, @tagName(tag), .{
+                                    const client_secret = hkdfExpandLabel(P.Hkdf, pv.master_secret, "c ap traffic", &handshake_hash, P.Hash.digest_length);
+                                    const server_secret = hkdfExpandLabel(P.Hkdf, pv.master_secret, "s ap traffic", &handshake_hash, P.Hash.digest_length);
+                                    break :app_cipher @unionInit(tls.ApplicationCipher, @tagName(tag), .{ .tls_1_3 = .{
                                         .client_secret = client_secret,
                                         .server_secret = server_secret,
                                         .client_key = hkdfExpandLabel(P.Hkdf, client_secret, "key", "", P.AEAD.key_length),
                                         .server_key = hkdfExpandLabel(P.Hkdf, server_secret, "key", "", P.AEAD.key_length),
                                         .client_iv = hkdfExpandLabel(P.Hkdf, client_secret, "iv", "", P.AEAD.nonce_length),
                                         .server_iv = hkdfExpandLabel(P.Hkdf, server_secret, "iv", "", P.AEAD.nonce_length),
-                                    });
+                                    } });
                                 },
-                            };
-                            const leftover = d.rest();
-                            var client: Client = .{
-                                .read_seq = 0,
-                                .write_seq = 0,
-                                .partial_cleartext_idx = 0,
-                                .partial_ciphertext_idx = 0,
-                                .partial_ciphertext_end = @intCast(leftover.len),
-                                .received_close_notify = false,
-                                .application_cipher = app_cipher,
-                                .partially_read_buffer = undefined,
-                            };
-                            @memcpy(client.partially_read_buffer[0..leftover.len], leftover);
-                            return client;
-                        },
-                        else => {
-                            return error.TlsUnexpectedMessage;
-                        },
-                    }
-                    if (ctd.eof()) break;
+                                .tls_1_2 => {
+                                    const pv = &p.version.tls_1_2;
+                                    try hsd.ensure(12);
+                                    if (!std.mem.eql(u8, hsd.array(12), &pv.server_verify_data)) return error.TlsDecryptError;
+                                    break :app_cipher @unionInit(tls.ApplicationCipher, @tagName(tag), .{ .tls_1_2 = pv.app_cipher });
+                                },
+                                else => unreachable,
+                            },
+                        };
+                        const leftover = d.rest();
+                        var client: Client = .{
+                            .tls_version = tls_version,
+                            .read_seq = switch (tls_version) {
+                                .tls_1_3 => 0,
+                                .tls_1_2 => read_seq,
+                                else => unreachable,
+                            },
+                            .write_seq = switch (tls_version) {
+                                .tls_1_3 => 0,
+                                .tls_1_2 => write_seq,
+                                else => unreachable,
+                            },
+                            .partial_cleartext_idx = 0,
+                            .partial_ciphertext_idx = 0,
+                            .partial_ciphertext_end = @intCast(leftover.len),
+                            .received_close_notify = false,
+                            .application_cipher = app_cipher,
+                            .partially_read_buffer = undefined,
+                        };
+                        @memcpy(client.partially_read_buffer[0..leftover.len], leftover);
+                        return client;
+                    },
+                    else => return error.TlsUnexpectedMessage,
                 }
+                if (ctd.eof()) break;
             },
-            else => {
-                return error.TlsUnexpectedMessage;
-            },
+            else => return error.TlsUnexpectedMessage,
         }
     }
 }
 
 /// Sends TLS-encrypted data to `stream`, which must conform to `StreamInterface`.
-/// Returns the number of plaintext bytes sent, which may be fewer than `bytes.len`.
+/// Returns the number of cleartext bytes sent, which may be fewer than `bytes.len`.
 pub fn write(c: *Client, stream: anytype, bytes: []const u8) !usize {
     return writeEnd(c, stream, bytes, false);
 }
@@ -749,7 +875,7 @@ pub fn writeAllEnd(c: *Client, stream: anytype, bytes: []const u8, end: bool) !v
 }
 
 /// Sends TLS-encrypted data to `stream`, which must conform to `StreamInterface`.
-/// Returns the number of plaintext bytes sent, which may be fewer than `bytes.len`.
+/// Returns the number of cleartext bytes sent, which may be fewer than `bytes.len`.
 /// If `end` is true, then this function additionally sends a `close_notify` alert,
 /// which is necessary for the server to distinguish between a properly finished
 /// TLS session, or a truncation attack.
@@ -813,62 +939,127 @@ fn prepareCiphertextRecord(
     var iovec_end: usize = 0;
     var bytes_i: usize = 0;
     switch (c.application_cipher) {
-        inline else => |*p| {
-            const P = @TypeOf(p.*);
-            const overhead_len = tls.record_header_len + P.AEAD.tag_length + 1;
-            const close_notify_alert_reserved = tls.close_notify_alert.len + overhead_len;
-            while (true) {
-                const encrypted_content_len: u16 = @intCast(@min(
-                    @min(bytes.len - bytes_i, tls.max_ciphertext_inner_record_len),
-                    ciphertext_buf.len -|
-                        (close_notify_alert_reserved + overhead_len + ciphertext_end),
-                ));
-                if (encrypted_content_len == 0) return .{
-                    .iovec_end = iovec_end,
-                    .ciphertext_end = ciphertext_end,
-                    .overhead_len = overhead_len,
-                };
-
-                @memcpy(cleartext_buf[0..encrypted_content_len], bytes[bytes_i..][0..encrypted_content_len]);
-                cleartext_buf[encrypted_content_len] = @intFromEnum(inner_content_type);
-                bytes_i += encrypted_content_len;
-                const ciphertext_len = encrypted_content_len + 1;
-                const cleartext = cleartext_buf[0..ciphertext_len];
-
-                const record_start = ciphertext_end;
-                const ad = ciphertext_buf[ciphertext_end..][0..5];
-                ad.* =
-                    [_]u8{@intFromEnum(tls.ContentType.application_data)} ++
-                    int2(@intFromEnum(tls.ProtocolVersion.tls_1_2)) ++
-                    int2(ciphertext_len + P.AEAD.tag_length);
-                ciphertext_end += ad.len;
-                const ciphertext = ciphertext_buf[ciphertext_end..][0..ciphertext_len];
-                ciphertext_end += ciphertext_len;
-                const auth_tag = ciphertext_buf[ciphertext_end..][0..P.AEAD.tag_length];
-                ciphertext_end += auth_tag.len;
-                const nonce = if (builtin.zig_backend == .stage2_x86_64 and
-                    P.AEAD.nonce_length > comptime std.simd.suggestVectorLength(u8) orelse 1)
-                nonce: {
-                    var nonce = p.client_iv;
-                    const operand = std.mem.readInt(u64, nonce[nonce.len - 8 ..], .big);
-                    std.mem.writeInt(u64, nonce[nonce.len - 8 ..], operand ^ c.write_seq, .big);
-                    break :nonce nonce;
-                } else nonce: {
-                    const V = @Vector(P.AEAD.nonce_length, u8);
-                    const pad = [1]u8{0} ** (P.AEAD.nonce_length - 8);
-                    const operand: V = pad ++ @as([8]u8, @bitCast(big(c.write_seq)));
-                    break :nonce @as(V, p.client_iv) ^ operand;
-                };
-                c.write_seq += 1; // TODO send key_update on overflow
-                P.AEAD.encrypt(ciphertext, auth_tag, cleartext, ad, nonce, p.client_key);
-
-                const record = ciphertext_buf[record_start..ciphertext_end];
-                iovecs[iovec_end] = .{
-                    .base = record.ptr,
-                    .len = record.len,
-                };
-                iovec_end += 1;
-            }
+        inline else => |*p| switch (c.tls_version) {
+            .tls_1_3 => {
+                const pv = &p.tls_1_3;
+                const P = @TypeOf(p.*);
+                const overhead_len = tls.record_header_len + P.AEAD.tag_length + 1;
+                const close_notify_alert_reserved = tls.close_notify_alert.len + overhead_len;
+                while (true) {
+                    const encrypted_content_len: u16 = @min(
+                        bytes.len - bytes_i,
+                        tls.max_ciphertext_inner_record_len,
+                        ciphertext_buf.len -|
+                            (close_notify_alert_reserved + overhead_len + ciphertext_end),
+                    );
+                    if (encrypted_content_len == 0) return .{
+                        .iovec_end = iovec_end,
+                        .ciphertext_end = ciphertext_end,
+                        .overhead_len = overhead_len,
+                    };
+
+                    @memcpy(cleartext_buf[0..encrypted_content_len], bytes[bytes_i..][0..encrypted_content_len]);
+                    cleartext_buf[encrypted_content_len] = @intFromEnum(inner_content_type);
+                    bytes_i += encrypted_content_len;
+                    const ciphertext_len = encrypted_content_len + 1;
+                    const cleartext = cleartext_buf[0..ciphertext_len];
+
+                    const record_start = ciphertext_end;
+                    const ad = ciphertext_buf[ciphertext_end..][0..tls.record_header_len];
+                    ad.* =
+                        [_]u8{@intFromEnum(tls.ContentType.application_data)} ++
+                        int2(@intFromEnum(tls.ProtocolVersion.tls_1_2)) ++
+                        int2(ciphertext_len + P.AEAD.tag_length);
+                    ciphertext_end += ad.len;
+                    const ciphertext = ciphertext_buf[ciphertext_end..][0..ciphertext_len];
+                    ciphertext_end += ciphertext_len;
+                    const auth_tag = ciphertext_buf[ciphertext_end..][0..P.AEAD.tag_length];
+                    ciphertext_end += auth_tag.len;
+                    const nonce = if (builtin.zig_backend == .stage2_x86_64 and
+                        P.AEAD.nonce_length > comptime std.simd.suggestVectorLength(u8) orelse 1)
+                    nonce: {
+                        var nonce = pv.client_iv;
+                        const operand = std.mem.readInt(u64, nonce[nonce.len - 8 ..], .big);
+                        std.mem.writeInt(u64, nonce[nonce.len - 8 ..], operand ^ c.write_seq, .big);
+                        break :nonce nonce;
+                    } else nonce: {
+                        const V = @Vector(P.AEAD.nonce_length, u8);
+                        const pad = [1]u8{0} ** (P.AEAD.nonce_length - 8);
+                        const operand: V = pad ++ std.mem.toBytes(big(c.write_seq));
+                        break :nonce @as(V, pv.client_iv) ^ operand;
+                    };
+                    P.AEAD.encrypt(ciphertext, auth_tag, cleartext, ad, nonce, pv.client_key);
+                    c.write_seq += 1; // TODO send key_update on overflow
+
+                    const record = ciphertext_buf[record_start..ciphertext_end];
+                    iovecs[iovec_end] = .{
+                        .base = record.ptr,
+                        .len = record.len,
+                    };
+                    iovec_end += 1;
+                }
+            },
+            .tls_1_2 => {
+                const pv = &p.tls_1_2;
+                const P = @TypeOf(p.*);
+                const overhead_len = tls.record_header_len + P.record_iv_length + P.mac_length;
+                const close_notify_alert_reserved = tls.close_notify_alert.len + overhead_len;
+                while (true) {
+                    const message_len: u16 = @min(
+                        bytes.len - bytes_i,
+                        tls.max_ciphertext_inner_record_len,
+                        ciphertext_buf.len -|
+                            (close_notify_alert_reserved + overhead_len + ciphertext_end),
+                    );
+                    if (message_len == 0) return .{
+                        .iovec_end = iovec_end,
+                        .ciphertext_end = ciphertext_end,
+                        .overhead_len = overhead_len,
+                    };
+
+                    @memcpy(cleartext_buf[0..message_len], bytes[bytes_i..][0..message_len]);
+                    bytes_i += message_len;
+                    const cleartext = cleartext_buf[0..message_len];
+
+                    const record_start = ciphertext_end;
+                    const record_header = ciphertext_buf[ciphertext_end..][0..tls.record_header_len];
+                    ciphertext_end += tls.record_header_len;
+                    record_header.* = [_]u8{@intFromEnum(inner_content_type)} ++
+                        int2(@intFromEnum(tls.ProtocolVersion.tls_1_2)) ++
+                        int2(P.record_iv_length + message_len + P.mac_length);
+                    const ad = std.mem.toBytes(big(c.write_seq)) ++ record_header[0 .. 1 + 2] ++ int2(message_len);
+                    const record_iv = ciphertext_buf[ciphertext_end..][0..P.record_iv_length];
+                    ciphertext_end += P.record_iv_length;
+                    const nonce: [P.AEAD.nonce_length]u8 = if (builtin.zig_backend == .stage2_x86_64 and
+                        P.AEAD.nonce_length > comptime std.simd.suggestVectorLength(u8) orelse 1)
+                    nonce: {
+                        var nonce = pv.client_write_IV ++ pv.client_salt;
+                        const operand = std.mem.readInt(u64, nonce[nonce.len - 8 ..], .big);
+                        std.mem.writeInt(u64, nonce[nonce.len - 8 ..], operand ^ c.write_seq, .big);
+                        break :nonce nonce;
+                    } else nonce: {
+                        const V = @Vector(P.AEAD.nonce_length, u8);
+                        const pad = [1]u8{0} ** (P.AEAD.nonce_length - 8);
+                        const operand: V = pad ++ @as([8]u8, @bitCast(big(c.write_seq)));
+                        break :nonce @as(V, pv.client_write_IV ++ pv.client_salt) ^ operand;
+                    };
+                    record_iv.* = nonce[P.fixed_iv_length..].*;
+                    const ciphertext = ciphertext_buf[ciphertext_end..][0..message_len];
+                    ciphertext_end += message_len;
+                    const auth_tag = ciphertext_buf[ciphertext_end..][0..P.mac_length];
+                    ciphertext_end += P.mac_length;
+                    P.AEAD.encrypt(ciphertext, auth_tag, cleartext, ad, nonce, pv.client_write_key);
+                    c.write_seq += 1; // TODO send key_update on overflow
+
+                    const record = ciphertext_buf[record_start..ciphertext_end];
+                    iovecs[iovec_end] = .{
+                        .base = record.ptr,
+                        .len = record.len,
+                    };
+                    iovec_end += 1;
+                }
+            },
+            else => unreachable,
         },
     }
 }
@@ -990,7 +1181,7 @@ pub fn readvAdvanced(c: *Client, stream: anytype, iovecs: []const std.posix.iove
     // beginning of the buffer will be used for such purposes.
     const cleartext_buf_len = free_size - ciphertext_buf_len;
 
-    // Recoup `partially_read_buffer space`. This is necessary because it is assumed
+    // Recoup `partially_read_buffer` space. This is necessary because it is assumed
     // below that `frag0` is big enough to hold at least one record.
     limitedOverlapCopy(c.partially_read_buffer[0..c.partial_ciphertext_end], c.partial_ciphertext_idx);
     c.partial_ciphertext_end -= c.partial_ciphertext_idx;
@@ -1105,159 +1296,182 @@ pub fn readvAdvanced(c: *Client, stream: anytype, iovecs: []const std.posix.iove
             in = 0;
             continue;
         }
-        switch (ct) {
+        const cleartext, const inner_ct: tls.ContentType = cleartext: switch (c.application_cipher) {
+            inline else => |*p| switch (c.tls_version) {
+                .tls_1_3 => {
+                    const pv = &p.tls_1_3;
+                    const P = @TypeOf(p.*);
+                    const ad = frag[in - tls.record_header_len ..][0..tls.record_header_len];
+                    const ciphertext_len = record_len - P.AEAD.tag_length;
+                    const ciphertext = frag[in..][0..ciphertext_len];
+                    in += ciphertext_len;
+                    const auth_tag = frag[in..][0..P.AEAD.tag_length].*;
+                    const nonce = if (builtin.zig_backend == .stage2_x86_64 and
+                        P.AEAD.nonce_length > comptime std.simd.suggestVectorLength(u8) orelse 1)
+                    nonce: {
+                        var nonce = pv.server_iv;
+                        const operand = std.mem.readInt(u64, nonce[nonce.len - 8 ..], .big);
+                        std.mem.writeInt(u64, nonce[nonce.len - 8 ..], operand ^ c.read_seq, .big);
+                        break :nonce nonce;
+                    } else nonce: {
+                        const V = @Vector(P.AEAD.nonce_length, u8);
+                        const pad = [1]u8{0} ** (P.AEAD.nonce_length - 8);
+                        const operand: V = pad ++ std.mem.toBytes(big(c.read_seq));
+                        break :nonce @as(V, pv.server_iv) ^ operand;
+                    };
+                    const out_buf = vp.peek();
+                    const cleartext_buf = if (ciphertext.len <= out_buf.len)
+                        out_buf
+                    else
+                        &cleartext_stack_buffer;
+                    const cleartext = cleartext_buf[0..ciphertext.len];
+                    P.AEAD.decrypt(cleartext, ciphertext, auth_tag, ad, nonce, pv.server_key) catch
+                        return error.TlsBadRecordMac;
+                    const msg = mem.trimRight(u8, cleartext, "\x00");
+                    break :cleartext .{ msg[0 .. msg.len - 1], @enumFromInt(msg[msg.len - 1]) };
+                },
+                .tls_1_2 => {
+                    const pv = &p.tls_1_2;
+                    const P = @TypeOf(p.*);
+                    const message_len: u16 = record_len - P.record_iv_length - P.mac_length;
+                    const ad = std.mem.toBytes(big(c.read_seq)) ++
+                        frag[in - tls.record_header_len ..][0 .. 1 + 2] ++
+                        std.mem.toBytes(big(message_len));
+                    const record_iv = frag[in..][0..P.record_iv_length].*;
+                    in += P.record_iv_length;
+                    const masked_read_seq = c.read_seq &
+                        comptime std.math.shl(u64, std.math.maxInt(u64), 8 * P.record_iv_length);
+                    const nonce: [P.AEAD.nonce_length]u8 = if (builtin.zig_backend == .stage2_x86_64 and
+                        P.AEAD.nonce_length > comptime std.simd.suggestVectorLength(u8) orelse 1)
+                    nonce: {
+                        var nonce = pv.server_write_IV ++ record_iv;
+                        const operand = std.mem.readInt(u64, nonce[nonce.len - 8 ..], .big);
+                        std.mem.writeInt(u64, nonce[nonce.len - 8 ..], operand ^ masked_read_seq, .big);
+                        break :nonce nonce;
+                    } else nonce: {
+                        const V = @Vector(P.AEAD.nonce_length, u8);
+                        const pad = [1]u8{0} ** (P.AEAD.nonce_length - 8);
+                        const operand: V = pad ++ @as([8]u8, @bitCast(big(masked_read_seq)));
+                        break :nonce @as(V, pv.server_write_IV ++ record_iv) ^ operand;
+                    };
+                    const ciphertext = frag[in..][0..message_len];
+                    in += message_len;
+                    const auth_tag = frag[in..][0..P.mac_length].*;
+                    in += P.mac_length;
+                    const out_buf = vp.peek();
+                    const cleartext_buf = if (message_len <= out_buf.len)
+                        out_buf
+                    else
+                        &cleartext_stack_buffer;
+                    const cleartext = cleartext_buf[0..ciphertext.len];
+                    P.AEAD.decrypt(cleartext, ciphertext, auth_tag, ad, nonce, pv.server_write_key) catch
+                        return error.TlsBadRecordMac;
+                    break :cleartext .{ cleartext, ct };
+                },
+                else => unreachable,
+            },
+        };
+        c.read_seq = try std.math.add(u64, c.read_seq, 1);
+        switch (inner_ct) {
             .alert => {
-                if (in + 2 > frag.len) return error.TlsDecodeError;
-                const level: tls.AlertLevel = @enumFromInt(frag[in]);
-                const desc: tls.AlertDescription = @enumFromInt(frag[in + 1]);
+                if (cleartext.len != 2) return error.TlsDecodeError;
+                const level: tls.AlertLevel = @enumFromInt(cleartext[0]);
+                const desc: tls.AlertDescription = @enumFromInt(cleartext[1]);
+                if (desc == .close_notify) {
+                    c.received_close_notify = true;
+                    c.partial_ciphertext_end = c.partial_ciphertext_idx;
+                    return vp.total;
+                }
                 _ = level;
 
                 try desc.toError();
                 // TODO: handle server-side closures
                 return error.TlsUnexpectedMessage;
             },
-            .application_data => {
-                const cleartext = switch (c.application_cipher) {
-                    inline else => |*p| c: {
-                        const P = @TypeOf(p.*);
-                        const ad = frag[in - 5 ..][0..5];
-                        const ciphertext_len = record_len - P.AEAD.tag_length;
-                        const ciphertext = frag[in..][0..ciphertext_len];
-                        in += ciphertext_len;
-                        const auth_tag = frag[in..][0..P.AEAD.tag_length].*;
-                        const nonce = if (builtin.zig_backend == .stage2_x86_64 and
-                            P.AEAD.nonce_length > comptime std.simd.suggestVectorLength(u8) orelse 1)
-                        nonce: {
-                            var nonce = p.server_iv;
-                            const operand = std.mem.readInt(u64, nonce[nonce.len - 8 ..], .big);
-                            std.mem.writeInt(u64, nonce[nonce.len - 8 ..], operand ^ c.read_seq, .big);
-                            break :nonce nonce;
-                        } else nonce: {
-                            const V = @Vector(P.AEAD.nonce_length, u8);
-                            const pad = [1]u8{0} ** (P.AEAD.nonce_length - 8);
-                            const operand: V = pad ++ @as([8]u8, @bitCast(big(c.read_seq)));
-                            break :nonce @as(V, p.server_iv) ^ operand;
-                        };
-                        const out_buf = vp.peek();
-                        const cleartext_buf = if (ciphertext.len <= out_buf.len)
-                            out_buf
-                        else
-                            &cleartext_stack_buffer;
-                        const cleartext = cleartext_buf[0..ciphertext.len];
-                        P.AEAD.decrypt(cleartext, ciphertext, auth_tag, ad, nonce, p.server_key) catch
-                            return error.TlsBadRecordMac;
-                        break :c mem.trimRight(u8, cleartext, "\x00");
-                    },
-                };
-
-                c.read_seq = try std.math.add(u64, c.read_seq, 1);
-
-                const inner_ct: tls.ContentType = @enumFromInt(cleartext[cleartext.len - 1]);
-                switch (inner_ct) {
-                    .alert => {
-                        const level: tls.AlertLevel = @enumFromInt(cleartext[0]);
-                        const desc: tls.AlertDescription = @enumFromInt(cleartext[1]);
-                        if (desc == .close_notify) {
-                            c.received_close_notify = true;
-                            c.partial_ciphertext_end = c.partial_ciphertext_idx;
-                            return vp.total;
-                        }
-                        _ = level;
-
-                        try desc.toError();
-                        // TODO: handle server-side closures
-                        return error.TlsUnexpectedMessage;
-                    },
-                    .handshake => {
-                        var ct_i: usize = 0;
-                        while (true) {
-                            const handshake_type: tls.HandshakeType = @enumFromInt(cleartext[ct_i]);
-                            ct_i += 1;
-                            const handshake_len = mem.readInt(u24, cleartext[ct_i..][0..3], .big);
-                            ct_i += 3;
-                            const next_handshake_i = ct_i + handshake_len;
-                            if (next_handshake_i > cleartext.len - 1)
-                                return error.TlsBadLength;
-                            const handshake = cleartext[ct_i..next_handshake_i];
-                            switch (handshake_type) {
-                                .new_session_ticket => {
-                                    // This client implementation ignores new session tickets.
+            .handshake => {
+                var ct_i: usize = 0;
+                while (true) {
+                    const handshake_type: tls.HandshakeType = @enumFromInt(cleartext[ct_i]);
+                    ct_i += 1;
+                    const handshake_len = mem.readInt(u24, cleartext[ct_i..][0..3], .big);
+                    ct_i += 3;
+                    const next_handshake_i = ct_i + handshake_len;
+                    if (next_handshake_i > cleartext.len)
+                        return error.TlsBadLength;
+                    const handshake = cleartext[ct_i..next_handshake_i];
+                    switch (handshake_type) {
+                        .new_session_ticket => {
+                            // This client implementation ignores new session tickets.
+                        },
+                        .key_update => {
+                            switch (c.application_cipher) {
+                                inline else => |*p| {
+                                    const pv = &p.tls_1_3;
+                                    const P = @TypeOf(p.*);
+                                    const server_secret = hkdfExpandLabel(P.Hkdf, pv.server_secret, "traffic upd", "", P.Hash.digest_length);
+                                    pv.server_secret = server_secret;
+                                    pv.server_key = hkdfExpandLabel(P.Hkdf, server_secret, "key", "", P.AEAD.key_length);
+                                    pv.server_iv = hkdfExpandLabel(P.Hkdf, server_secret, "iv", "", P.AEAD.nonce_length);
                                 },
-                                .key_update => {
+                            }
+                            c.read_seq = 0;
+
+                            switch (@as(tls.KeyUpdateRequest, @enumFromInt(handshake[0]))) {
+                                .update_requested => {
                                     switch (c.application_cipher) {
                                         inline else => |*p| {
+                                            const pv = &p.tls_1_3;
                                             const P = @TypeOf(p.*);
-                                            const server_secret = hkdfExpandLabel(P.Hkdf, p.server_secret, "traffic upd", "", P.Hash.digest_length);
-                                            p.server_secret = server_secret;
-                                            p.server_key = hkdfExpandLabel(P.Hkdf, server_secret, "key", "", P.AEAD.key_length);
-                                            p.server_iv = hkdfExpandLabel(P.Hkdf, server_secret, "iv", "", P.AEAD.nonce_length);
-                                        },
-                                    }
-                                    c.read_seq = 0;
-
-                                    switch (@as(tls.KeyUpdateRequest, @enumFromInt(handshake[0]))) {
-                                        .update_requested => {
-                                            switch (c.application_cipher) {
-                                                inline else => |*p| {
-                                                    const P = @TypeOf(p.*);
-                                                    const client_secret = hkdfExpandLabel(P.Hkdf, p.client_secret, "traffic upd", "", P.Hash.digest_length);
-                                                    p.client_secret = client_secret;
-                                                    p.client_key = hkdfExpandLabel(P.Hkdf, client_secret, "key", "", P.AEAD.key_length);
-                                                    p.client_iv = hkdfExpandLabel(P.Hkdf, client_secret, "iv", "", P.AEAD.nonce_length);
-                                                },
-                                            }
-                                            c.write_seq = 0;
+                                            const client_secret = hkdfExpandLabel(P.Hkdf, pv.client_secret, "traffic upd", "", P.Hash.digest_length);
+                                            pv.client_secret = client_secret;
+                                            pv.client_key = hkdfExpandLabel(P.Hkdf, client_secret, "key", "", P.AEAD.key_length);
+                                            pv.client_iv = hkdfExpandLabel(P.Hkdf, client_secret, "iv", "", P.AEAD.nonce_length);
                                         },
-                                        .update_not_requested => {},
-                                        _ => return error.TlsIllegalParameter,
                                     }
+                                    c.write_seq = 0;
                                 },
-                                else => {
-                                    return error.TlsUnexpectedMessage;
-                                },
-                            }
-                            ct_i = next_handshake_i;
-                            if (ct_i >= cleartext.len - 1) break;
-                        }
-                    },
-                    .application_data => {
-                        // Determine whether the output buffer or a stack
-                        // buffer was used for storing the cleartext.
-                        if (cleartext.ptr == &cleartext_stack_buffer) {
-                            // Stack buffer was used, so we must copy to the output buffer.
-                            const msg = cleartext[0 .. cleartext.len - 1];
-                            if (c.partial_ciphertext_idx > c.partial_cleartext_idx) {
-                                // We have already run out of room in iovecs. Continue
-                                // appending to `partially_read_buffer`.
-                                @memcpy(
-                                    c.partially_read_buffer[c.partial_ciphertext_idx..][0..msg.len],
-                                    msg,
-                                );
-                                c.partial_ciphertext_idx = @intCast(c.partial_ciphertext_idx + msg.len);
-                            } else {
-                                const amt = vp.put(msg);
-                                if (amt < msg.len) {
-                                    const rest = msg[amt..];
-                                    c.partial_cleartext_idx = 0;
-                                    c.partial_ciphertext_idx = @intCast(rest.len);
-                                    @memcpy(c.partially_read_buffer[0..rest.len], rest);
-                                }
+                                .update_not_requested => {},
+                                _ => return error.TlsIllegalParameter,
                             }
-                        } else {
-                            // Output buffer was used directly which means no
-                            // memory copying needs to occur, and we can move
-                            // on to the next ciphertext record.
-                            vp.next(cleartext.len - 1);
-                        }
-                    },
-                    else => {
-                        return error.TlsUnexpectedMessage;
-                    },
+                        },
+                        else => {
+                            return error.TlsUnexpectedMessage;
+                        },
+                    }
+                    ct_i = next_handshake_i;
+                    if (ct_i >= cleartext.len) break;
                 }
             },
-            else => {
-                return error.TlsUnexpectedMessage;
+            .application_data => {
+                // Determine whether the output buffer or a stack
+                // buffer was used for storing the cleartext.
+                if (cleartext.ptr == &cleartext_stack_buffer) {
+                    // Stack buffer was used, so we must copy to the output buffer.
+                    if (c.partial_ciphertext_idx > c.partial_cleartext_idx) {
+                        // We have already run out of room in iovecs. Continue
+                        // appending to `partially_read_buffer`.
+                        @memcpy(
+                            c.partially_read_buffer[c.partial_ciphertext_idx..][0..cleartext.len],
+                            cleartext,
+                        );
+                        c.partial_ciphertext_idx = @intCast(c.partial_ciphertext_idx + cleartext.len);
+                    } else {
+                        const amt = vp.put(cleartext);
+                        if (amt < cleartext.len) {
+                            const rest = cleartext[amt..];
+                            c.partial_cleartext_idx = 0;
+                            c.partial_ciphertext_idx = @intCast(rest.len);
+                            @memcpy(c.partially_read_buffer[0..rest.len], rest);
+                        }
+                    }
+                } else {
+                    // Output buffer was used directly which means no
+                    // memory copying needs to occur, and we can move
+                    // on to the next ciphertext record.
+                    vp.next(cleartext.len);
+                }
             },
+            else => return error.TlsUnexpectedMessage,
         }
         in = end;
     }
@@ -1326,6 +1540,74 @@ inline fn big(x: anytype) @TypeOf(x) {
     };
 }
 
+const KeyShare = struct {
+    x25519_kp: crypto.dh.X25519.KeyPair,
+    secp256r1_kp: crypto.sign.ecdsa.EcdsaP256Sha256.KeyPair,
+    ml_kem768_kp: crypto.kem.ml_kem.MLKem768.KeyPair,
+    sk_buf: [sk_max_len]u8,
+    sk_len: std.math.IntFittingRange(0, sk_max_len),
+
+    const sk_max_len = @max(
+        crypto.dh.X25519.shared_length + crypto.kem.ml_kem.MLKem768.shared_length,
+        crypto.dh.X25519.shared_length,
+        crypto.ecc.P256.scalar.encoded_length,
+    );
+
+    fn init(seed: [64]u8) error{IdentityElement}!KeyShare {
+        return .{
+            .x25519_kp = try .create(seed[0..32].*),
+            .secp256r1_kp = try .create(seed[32..64].*),
+            .ml_kem768_kp = try .create(null),
+            .sk_buf = undefined,
+            .sk_len = 0,
+        };
+    }
+
+    fn exchange(
+        ks: *KeyShare,
+        named_group: tls.NamedGroup,
+        server_pub_key: []const u8,
+    ) error{ TlsIllegalParameter, TlsDecryptFailure }!void {
+        switch (named_group) {
+            .x25519_ml_kem768 => {
+                const xksl = crypto.dh.X25519.public_length;
+                const hksl = xksl + crypto.kem.ml_kem.MLKem768.ciphertext_length;
+                if (server_pub_key.len != hksl) return error.TlsIllegalParameter;
+
+                const xsk = crypto.dh.X25519.scalarmult(ks.x25519_kp.secret_key, server_pub_key[0..xksl].*) catch
+                    return error.TlsDecryptFailure;
+                const hsk = ks.ml_kem768_kp.secret_key.decaps(server_pub_key[xksl..hksl]) catch
+                    return error.TlsDecryptFailure;
+                @memcpy(ks.sk_buf[0..xsk.len], &xsk);
+                @memcpy(ks.sk_buf[xsk.len..][0..hsk.len], &hsk);
+                ks.sk_len = xsk.len + hsk.len;
+            },
+            .x25519 => {
+                const ksl = crypto.dh.X25519.public_length;
+                if (server_pub_key.len != ksl) return error.TlsIllegalParameter;
+                const sk = crypto.dh.X25519.scalarmult(ks.x25519_kp.secret_key, server_pub_key[0..ksl].*) catch
+                    return error.TlsDecryptFailure;
+                @memcpy(ks.sk_buf[0..sk.len], &sk);
+                ks.sk_len = sk.len;
+            },
+            .secp256r1 => {
+                const PublicKey = crypto.sign.ecdsa.EcdsaP256Sha256.PublicKey;
+                const pk = PublicKey.fromSec1(server_pub_key) catch return error.TlsDecryptFailure;
+                const mul = pk.p.mulPublic(ks.secp256r1_kp.secret_key.bytes, .big) catch
+                    return error.TlsDecryptFailure;
+                const sk = mul.affineCoordinates().x.toBytes(.big);
+                @memcpy(ks.sk_buf[0..sk.len], &sk);
+                ks.sk_len = sk.len;
+            },
+            else => return error.TlsIllegalParameter,
+        }
+    }
+
+    fn getSharedSecret(ks: *const KeyShare) ?[]const u8 {
+        return if (ks.sk_len > 0) ks.sk_buf[0..ks.sk_len] else null;
+    }
+};
+
 fn SchemeEcdsa(comptime scheme: tls.SignatureScheme) type {
     return switch (scheme) {
         .ecdsa_secp256r1_sha256 => crypto.sign.ecdsa.EcdsaP256Sha256,
@@ -1334,11 +1616,20 @@ fn SchemeEcdsa(comptime scheme: tls.SignatureScheme) type {
     };
 }
 
-fn SchemeHash(comptime scheme: tls.SignatureScheme) type {
+fn SchemeRsa(comptime scheme: tls.SignatureScheme) type {
     return switch (scheme) {
-        .rsa_pss_rsae_sha256 => crypto.hash.sha2.Sha256,
-        .rsa_pss_rsae_sha384 => crypto.hash.sha2.Sha384,
-        .rsa_pss_rsae_sha512 => crypto.hash.sha2.Sha512,
+        .rsa_pkcs1_sha256,
+        .rsa_pkcs1_sha384,
+        .rsa_pkcs1_sha512,
+        .rsa_pkcs1_sha1,
+        => Certificate.rsa.PKCS1v1_5Signature,
+        .rsa_pss_rsae_sha256,
+        .rsa_pss_rsae_sha384,
+        .rsa_pss_rsae_sha512,
+        .rsa_pss_pss_sha256,
+        .rsa_pss_pss_sha384,
+        .rsa_pss_pss_sha512,
+        => Certificate.rsa.PSSSignature,
         else => @compileError("bad scheme"),
     };
 }
@@ -1350,6 +1641,142 @@ fn SchemeEddsa(comptime scheme: tls.SignatureScheme) type {
     };
 }
 
+fn SchemeHash(comptime scheme: tls.SignatureScheme) type {
+    return switch (scheme) {
+        .rsa_pkcs1_sha256,
+        .ecdsa_secp256r1_sha256,
+        .rsa_pss_rsae_sha256,
+        .rsa_pss_pss_sha256,
+        => crypto.hash.sha2.Sha256,
+        .rsa_pkcs1_sha384,
+        .ecdsa_secp384r1_sha384,
+        .rsa_pss_rsae_sha384,
+        .rsa_pss_pss_sha384,
+        => crypto.hash.sha2.Sha384,
+        .rsa_pkcs1_sha512,
+        .ecdsa_secp521r1_sha512,
+        .rsa_pss_rsae_sha512,
+        .rsa_pss_pss_sha512,
+        => crypto.hash.sha2.Sha512,
+        .rsa_pkcs1_sha1,
+        .ecdsa_sha1,
+        => crypto.hash.Sha1,
+        else => @compileError("bad scheme"),
+    };
+}
+
+const CertificatePublicKey = struct {
+    algo: Certificate.AlgorithmCategory,
+    buf: [600]u8,
+    len: u16,
+
+    fn init(
+        cert_pub_key: *CertificatePublicKey,
+        algo: Certificate.AlgorithmCategory,
+        pub_key: []const u8,
+    ) error{CertificatePublicKeyInvalid}!void {
+        if (pub_key.len > cert_pub_key.buf.len) return error.CertificatePublicKeyInvalid;
+        cert_pub_key.algo = algo;
+        @memcpy(cert_pub_key.buf[0..pub_key.len], pub_key);
+        cert_pub_key.len = @intCast(pub_key.len);
+    }
+
+    const VerifyError = error{ TlsDecodeError, TlsBadSignatureScheme, InvalidEncoding } ||
+        // ecdsa
+        crypto.errors.EncodingError ||
+        crypto.errors.NotSquareError ||
+        crypto.errors.NonCanonicalError ||
+        SchemeEcdsa(.ecdsa_secp256r1_sha256).Signature.VerifyError ||
+        SchemeEcdsa(.ecdsa_secp384r1_sha384).Signature.VerifyError ||
+        // rsa
+        error{TlsBadRsaSignatureBitCount} ||
+        Certificate.rsa.PublicKey.ParseDerError ||
+        Certificate.rsa.PublicKey.FromBytesError ||
+        Certificate.rsa.PSSSignature.VerifyError ||
+        Certificate.rsa.PKCS1v1_5Signature.VerifyError ||
+        // eddsa
+        SchemeEddsa(.ed25519).Signature.VerifyError;
+
+    fn verifySignature(
+        cert_pub_key: *const CertificatePublicKey,
+        sigd: *tls.Decoder,
+        msg: []const []const u8,
+    ) VerifyError!void {
+        const pub_key = cert_pub_key.buf[0..cert_pub_key.len];
+
+        try sigd.ensure(2 + 2);
+        const scheme = sigd.decode(tls.SignatureScheme);
+        const sig_len = sigd.decode(u16);
+        try sigd.ensure(sig_len);
+        const encoded_sig = sigd.slice(sig_len);
+
+        if (cert_pub_key.algo != @as(Certificate.AlgorithmCategory, switch (scheme) {
+            .ecdsa_secp256r1_sha256,
+            .ecdsa_secp384r1_sha384,
+            => .X9_62_id_ecPublicKey,
+            .rsa_pkcs1_sha256,
+            .rsa_pkcs1_sha384,
+            .rsa_pkcs1_sha512,
+            .rsa_pss_rsae_sha256,
+            .rsa_pss_rsae_sha384,
+            .rsa_pss_rsae_sha512,
+            .rsa_pkcs1_sha1,
+            => .rsaEncryption,
+            .rsa_pss_pss_sha256,
+            .rsa_pss_pss_sha384,
+            .rsa_pss_pss_sha512,
+            => .rsassa_pss,
+            else => return error.TlsBadSignatureScheme,
+        })) return error.TlsBadSignatureScheme;
+
+        switch (scheme) {
+            inline .ecdsa_secp256r1_sha256,
+            .ecdsa_secp384r1_sha384,
+            => |comptime_scheme| {
+                const Ecdsa = SchemeEcdsa(comptime_scheme);
+                const sig = try Ecdsa.Signature.fromDer(encoded_sig);
+                const key = try Ecdsa.PublicKey.fromSec1(pub_key);
+                try sig.concatVerify(msg, key);
+            },
+            inline .rsa_pkcs1_sha256,
+            .rsa_pkcs1_sha384,
+            .rsa_pkcs1_sha512,
+            .rsa_pss_rsae_sha256,
+            .rsa_pss_rsae_sha384,
+            .rsa_pss_rsae_sha512,
+            .rsa_pss_pss_sha256,
+            .rsa_pss_pss_sha384,
+            .rsa_pss_pss_sha512,
+            .rsa_pkcs1_sha1,
+            => |comptime_scheme| {
+                const RsaSignature = SchemeRsa(comptime_scheme);
+                const Hash = SchemeHash(comptime_scheme);
+                const PublicKey = Certificate.rsa.PublicKey;
+                const components = try PublicKey.parseDer(pub_key);
+                const exponent = components.exponent;
+                const modulus = components.modulus;
+                switch (modulus.len) {
+                    inline 128, 256, 512 => |modulus_len| {
+                        const key: PublicKey = try .fromBytes(exponent, modulus);
+                        const sig = RsaSignature.fromBytes(modulus_len, encoded_sig);
+                        try RsaSignature.concatVerify(modulus_len, sig, msg, key, Hash);
+                    },
+                    else => return error.TlsBadRsaSignatureBitCount,
+                }
+            },
+            inline .ed25519 => |comptime_scheme| {
+                const Eddsa = SchemeEddsa(comptime_scheme);
+                if (encoded_sig.len != Eddsa.Signature.encoded_length) return error.InvalidEncoding;
+                const sig = Eddsa.Signature.fromBytes(encoded_sig[0..Eddsa.Signature.encoded_length].*);
+                if (pub_key.len != Eddsa.PublicKey.encoded_length) return error.InvalidEncoding;
+                const key = try Eddsa.PublicKey.fromBytes(pub_key[0..Eddsa.PublicKey.encoded_length].*);
+                try sig.concatVerify(msg, key);
+            },
+            else => unreachable,
+        }
+    }
+};
+
 /// Abstraction for sending multiple byte buffers to a slice of iovecs.
 const VecPut = struct {
     iovecs: []const std.posix.iovec,
@@ -1451,16 +1878,22 @@ const cipher_suites = if (crypto.core.aes.has_hardware_support)
         .AEGIS_128L_SHA256,
         .AEGIS_256_SHA512,
         .AES_128_GCM_SHA256,
+        .ECDHE_RSA_WITH_AES_128_GCM_SHA256,
         .AES_256_GCM_SHA384,
+        .ECDHE_RSA_WITH_AES_256_GCM_SHA384,
         .CHACHA20_POLY1305_SHA256,
+        .ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
     })
 else
     enum_array(tls.CipherSuite, &.{
         .CHACHA20_POLY1305_SHA256,
+        .ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
         .AEGIS_128L_SHA256,
         .AEGIS_256_SHA512,
         .AES_128_GCM_SHA256,
+        .ECDHE_RSA_WITH_AES_128_GCM_SHA256,
         .AES_256_GCM_SHA384,
+        .ECDHE_RSA_WITH_AES_256_GCM_SHA384,
     });
 
 test {
lib/std/crypto/Certificate.zig
@@ -20,18 +20,18 @@ pub const Algorithm = enum {
     curveEd25519,
 
     pub const map = std.StaticStringMap(Algorithm).initComptime(.{
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x05 }, .sha1WithRSAEncryption },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x0B }, .sha256WithRSAEncryption },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x0C }, .sha384WithRSAEncryption },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x0D }, .sha512WithRSAEncryption },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x0E }, .sha224WithRSAEncryption },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x04, 0x03, 0x01 }, .ecdsa_with_SHA224 },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x04, 0x03, 0x02 }, .ecdsa_with_SHA256 },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x04, 0x03, 0x03 }, .ecdsa_with_SHA384 },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x04, 0x03, 0x04 }, .ecdsa_with_SHA512 },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x02 }, .md2WithRSAEncryption },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x04 }, .md5WithRSAEncryption },
-        .{ &[_]u8{ 0x2B, 0x65, 0x70 }, .curveEd25519 },
+        .{ &.{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x05 }, .sha1WithRSAEncryption },
+        .{ &.{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x0B }, .sha256WithRSAEncryption },
+        .{ &.{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x0C }, .sha384WithRSAEncryption },
+        .{ &.{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x0D }, .sha512WithRSAEncryption },
+        .{ &.{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x0E }, .sha224WithRSAEncryption },
+        .{ &.{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x04, 0x03, 0x01 }, .ecdsa_with_SHA224 },
+        .{ &.{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x04, 0x03, 0x02 }, .ecdsa_with_SHA256 },
+        .{ &.{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x04, 0x03, 0x03 }, .ecdsa_with_SHA384 },
+        .{ &.{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x04, 0x03, 0x04 }, .ecdsa_with_SHA512 },
+        .{ &.{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x02 }, .md2WithRSAEncryption },
+        .{ &.{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x04 }, .md5WithRSAEncryption },
+        .{ &.{ 0x2B, 0x65, 0x70 }, .curveEd25519 },
     });
 
     pub fn Hash(comptime algorithm: Algorithm) type {
@@ -49,13 +49,15 @@ pub const Algorithm = enum {
 
 pub const AlgorithmCategory = enum {
     rsaEncryption,
+    rsassa_pss,
     X9_62_id_ecPublicKey,
     curveEd25519,
 
     pub const map = std.StaticStringMap(AlgorithmCategory).initComptime(.{
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01 }, .rsaEncryption },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x02, 0x01 }, .X9_62_id_ecPublicKey },
-        .{ &[_]u8{ 0x2B, 0x65, 0x70 }, .curveEd25519 },
+        .{ &.{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01 }, .rsaEncryption },
+        .{ &.{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x0A }, .rsassa_pss },
+        .{ &.{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x02, 0x01 }, .X9_62_id_ecPublicKey },
+        .{ &.{ 0x2B, 0x65, 0x70 }, .curveEd25519 },
     });
 };
 
@@ -74,18 +76,18 @@ pub const Attribute = enum {
     domainComponent,
 
     pub const map = std.StaticStringMap(Attribute).initComptime(.{
-        .{ &[_]u8{ 0x55, 0x04, 0x03 }, .commonName },
-        .{ &[_]u8{ 0x55, 0x04, 0x05 }, .serialNumber },
-        .{ &[_]u8{ 0x55, 0x04, 0x06 }, .countryName },
-        .{ &[_]u8{ 0x55, 0x04, 0x07 }, .localityName },
-        .{ &[_]u8{ 0x55, 0x04, 0x08 }, .stateOrProvinceName },
-        .{ &[_]u8{ 0x55, 0x04, 0x09 }, .streetAddress },
-        .{ &[_]u8{ 0x55, 0x04, 0x0A }, .organizationName },
-        .{ &[_]u8{ 0x55, 0x04, 0x0B }, .organizationalUnitName },
-        .{ &[_]u8{ 0x55, 0x04, 0x11 }, .postalCode },
-        .{ &[_]u8{ 0x55, 0x04, 0x61 }, .organizationIdentifier },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x09, 0x01 }, .pkcs9_emailAddress },
-        .{ &[_]u8{ 0x09, 0x92, 0x26, 0x89, 0x93, 0xF2, 0x2C, 0x64, 0x01, 0x19 }, .domainComponent },
+        .{ &.{ 0x55, 0x04, 0x03 }, .commonName },
+        .{ &.{ 0x55, 0x04, 0x05 }, .serialNumber },
+        .{ &.{ 0x55, 0x04, 0x06 }, .countryName },
+        .{ &.{ 0x55, 0x04, 0x07 }, .localityName },
+        .{ &.{ 0x55, 0x04, 0x08 }, .stateOrProvinceName },
+        .{ &.{ 0x55, 0x04, 0x09 }, .streetAddress },
+        .{ &.{ 0x55, 0x04, 0x0A }, .organizationName },
+        .{ &.{ 0x55, 0x04, 0x0B }, .organizationalUnitName },
+        .{ &.{ 0x55, 0x04, 0x11 }, .postalCode },
+        .{ &.{ 0x55, 0x04, 0x61 }, .organizationIdentifier },
+        .{ &.{ 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x09, 0x01 }, .pkcs9_emailAddress },
+        .{ &.{ 0x09, 0x92, 0x26, 0x89, 0x93, 0xF2, 0x2C, 0x64, 0x01, 0x19 }, .domainComponent },
     });
 };
 
@@ -95,9 +97,9 @@ pub const NamedCurve = enum {
     X9_62_prime256v1,
 
     pub const map = std.StaticStringMap(NamedCurve).initComptime(.{
-        .{ &[_]u8{ 0x2B, 0x81, 0x04, 0x00, 0x22 }, .secp384r1 },
-        .{ &[_]u8{ 0x2B, 0x81, 0x04, 0x00, 0x23 }, .secp521r1 },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x03, 0x01, 0x07 }, .X9_62_prime256v1 },
+        .{ &.{ 0x2B, 0x81, 0x04, 0x00, 0x22 }, .secp384r1 },
+        .{ &.{ 0x2B, 0x81, 0x04, 0x00, 0x23 }, .secp521r1 },
+        .{ &.{ 0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x03, 0x01, 0x07 }, .X9_62_prime256v1 },
     });
 
     pub fn Curve(comptime curve: NamedCurve) type {
@@ -131,28 +133,28 @@ pub const ExtensionId = enum {
     netscape_comment,
 
     pub const map = std.StaticStringMap(ExtensionId).initComptime(.{
-        .{ &[_]u8{ 0x55, 0x04, 0x03 }, .commonName },
-        .{ &[_]u8{ 0x55, 0x1D, 0x01 }, .authority_key_identifier },
-        .{ &[_]u8{ 0x55, 0x1D, 0x07 }, .subject_alt_name },
-        .{ &[_]u8{ 0x55, 0x1D, 0x0E }, .subject_key_identifier },
-        .{ &[_]u8{ 0x55, 0x1D, 0x0F }, .key_usage },
-        .{ &[_]u8{ 0x55, 0x1D, 0x0A }, .basic_constraints },
-        .{ &[_]u8{ 0x55, 0x1D, 0x10 }, .private_key_usage_period },
-        .{ &[_]u8{ 0x55, 0x1D, 0x11 }, .subject_alt_name },
-        .{ &[_]u8{ 0x55, 0x1D, 0x12 }, .issuer_alt_name },
-        .{ &[_]u8{ 0x55, 0x1D, 0x13 }, .basic_constraints },
-        .{ &[_]u8{ 0x55, 0x1D, 0x14 }, .crl_number },
-        .{ &[_]u8{ 0x55, 0x1D, 0x1F }, .crl_distribution_points },
-        .{ &[_]u8{ 0x55, 0x1D, 0x20 }, .certificate_policies },
-        .{ &[_]u8{ 0x55, 0x1D, 0x23 }, .authority_key_identifier },
-        .{ &[_]u8{ 0x55, 0x1D, 0x25 }, .ext_key_usage },
-        .{ &[_]u8{ 0x2B, 0x06, 0x01, 0x04, 0x01, 0x82, 0x37, 0x15, 0x01 }, .msCertsrvCAVersion },
-        .{ &[_]u8{ 0x2B, 0x06, 0x01, 0x05, 0x05, 0x07, 0x01, 0x01 }, .info_access },
-        .{ &[_]u8{ 0x2A, 0x86, 0x48, 0x86, 0xF6, 0x7D, 0x07, 0x41, 0x00 }, .entrustVersInfo },
-        .{ &[_]u8{ 0x2b, 0x06, 0x01, 0x04, 0x01, 0x82, 0x37, 0x14, 0x02 }, .enroll_certtype },
-        .{ &[_]u8{ 0x2b, 0x06, 0x01, 0x05, 0x05, 0x07, 0x01, 0x0c }, .pe_logotype },
-        .{ &[_]u8{ 0x60, 0x86, 0x48, 0x01, 0x86, 0xf8, 0x42, 0x01, 0x01 }, .netscape_cert_type },
-        .{ &[_]u8{ 0x60, 0x86, 0x48, 0x01, 0x86, 0xf8, 0x42, 0x01, 0x0d }, .netscape_comment },
+        .{ &.{ 0x55, 0x04, 0x03 }, .commonName },
+        .{ &.{ 0x55, 0x1D, 0x01 }, .authority_key_identifier },
+        .{ &.{ 0x55, 0x1D, 0x07 }, .subject_alt_name },
+        .{ &.{ 0x55, 0x1D, 0x0E }, .subject_key_identifier },
+        .{ &.{ 0x55, 0x1D, 0x0F }, .key_usage },
+        .{ &.{ 0x55, 0x1D, 0x0A }, .basic_constraints },
+        .{ &.{ 0x55, 0x1D, 0x10 }, .private_key_usage_period },
+        .{ &.{ 0x55, 0x1D, 0x11 }, .subject_alt_name },
+        .{ &.{ 0x55, 0x1D, 0x12 }, .issuer_alt_name },
+        .{ &.{ 0x55, 0x1D, 0x13 }, .basic_constraints },
+        .{ &.{ 0x55, 0x1D, 0x14 }, .crl_number },
+        .{ &.{ 0x55, 0x1D, 0x1F }, .crl_distribution_points },
+        .{ &.{ 0x55, 0x1D, 0x20 }, .certificate_policies },
+        .{ &.{ 0x55, 0x1D, 0x23 }, .authority_key_identifier },
+        .{ &.{ 0x55, 0x1D, 0x25 }, .ext_key_usage },
+        .{ &.{ 0x2B, 0x06, 0x01, 0x04, 0x01, 0x82, 0x37, 0x15, 0x01 }, .msCertsrvCAVersion },
+        .{ &.{ 0x2B, 0x06, 0x01, 0x05, 0x05, 0x07, 0x01, 0x01 }, .info_access },
+        .{ &.{ 0x2A, 0x86, 0x48, 0x86, 0xF6, 0x7D, 0x07, 0x41, 0x00 }, .entrustVersInfo },
+        .{ &.{ 0x2b, 0x06, 0x01, 0x04, 0x01, 0x82, 0x37, 0x14, 0x02 }, .enroll_certtype },
+        .{ &.{ 0x2b, 0x06, 0x01, 0x05, 0x05, 0x07, 0x01, 0x0c }, .pe_logotype },
+        .{ &.{ 0x60, 0x86, 0x48, 0x01, 0x86, 0xf8, 0x42, 0x01, 0x01 }, .netscape_cert_type },
+        .{ &.{ 0x60, 0x86, 0x48, 0x01, 0x86, 0xf8, 0x42, 0x01, 0x0d }, .netscape_comment },
     });
 };
 
@@ -185,6 +187,7 @@ pub const Parsed = struct {
 
     pub const PubKeyAlgo = union(AlgorithmCategory) {
         rsaEncryption: void,
+        rsassa_pss: void,
         X9_62_id_ecPublicKey: NamedCurve,
         curveEd25519: void,
     };
@@ -386,7 +389,7 @@ test "Parsed.checkHostName" {
     try expectEqual(true, Parsed.checkHostName("bar.ziglang.org", "*.Ziglang.ORG"));
 }
 
-pub const ParseError = der.Element.ParseElementError || ParseVersionError || ParseTimeError || ParseEnumError || ParseBitStringError;
+pub const ParseError = der.Element.ParseError || ParseVersionError || ParseTimeError || ParseEnumError || ParseBitStringError;
 
 pub fn parse(cert: Certificate) ParseError!Parsed {
     const cert_bytes = cert.buffer;
@@ -413,13 +416,9 @@ pub fn parse(cert: Certificate) ParseError!Parsed {
     const pub_key_info = try der.Element.parse(cert_bytes, subject.slice.end);
     const pub_key_signature_algorithm = try der.Element.parse(cert_bytes, pub_key_info.slice.start);
     const pub_key_algo_elem = try der.Element.parse(cert_bytes, pub_key_signature_algorithm.slice.start);
-    const pub_key_algo_tag = try parseAlgorithmCategory(cert_bytes, pub_key_algo_elem);
-    var pub_key_algo: Parsed.PubKeyAlgo = undefined;
-    switch (pub_key_algo_tag) {
-        .rsaEncryption => {
-            pub_key_algo = .{ .rsaEncryption = {} };
-        },
-        .X9_62_id_ecPublicKey => {
+    const pub_key_algo: Parsed.PubKeyAlgo = switch (try parseAlgorithmCategory(cert_bytes, pub_key_algo_elem)) {
+        inline else => |tag| @unionInit(Parsed.PubKeyAlgo, @tagName(tag), {}),
+        .X9_62_id_ecPublicKey => pub_key_algo: {
             // RFC 5480 Section 2.1.1.1 Named Curve
             // ECParameters ::= CHOICE {
             //   namedCurve         OBJECT IDENTIFIER
@@ -428,12 +427,9 @@ pub fn parse(cert: Certificate) ParseError!Parsed {
             // }
             const params_elem = try der.Element.parse(cert_bytes, pub_key_algo_elem.slice.end);
             const named_curve = try parseNamedCurve(cert_bytes, params_elem);
-            pub_key_algo = .{ .X9_62_id_ecPublicKey = named_curve };
-        },
-        .curveEd25519 => {
-            pub_key_algo = .{ .curveEd25519 = {} };
+            break :pub_key_algo .{ .X9_62_id_ecPublicKey = named_curve };
         },
-    }
+    };
     const pub_key_elem = try der.Element.parse(cert_bytes, pub_key_signature_algorithm.slice.end);
     const pub_key = try parseBitString(cert, pub_key_elem);
 
@@ -731,7 +727,7 @@ pub fn parseVersion(bytes: []const u8, version_elem: der.Element) ParseVersionEr
 
 fn verifyRsa(
     comptime Hash: type,
-    message: []const u8,
+    msg: []const u8,
     sig: []const u8,
     pub_key_algo: Parsed.PubKeyAlgo,
     pub_key: []const u8,
@@ -743,59 +739,14 @@ fn verifyRsa(
     if (exponent.len > modulus.len) return error.CertificatePublicKeyInvalid;
     if (sig.len != modulus.len) return error.CertificateSignatureInvalidLength;
 
-    const hash_der = switch (Hash) {
-        crypto.hash.Sha1 => [_]u8{
-            0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e,
-            0x03, 0x02, 0x1a, 0x05, 0x00, 0x04, 0x14,
-        },
-        crypto.hash.sha2.Sha224 => [_]u8{
-            0x30, 0x2d, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
-            0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04, 0x05,
-            0x00, 0x04, 0x1c,
-        },
-        crypto.hash.sha2.Sha256 => [_]u8{
-            0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
-            0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05,
-            0x00, 0x04, 0x20,
-        },
-        crypto.hash.sha2.Sha384 => [_]u8{
-            0x30, 0x41, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
-            0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02, 0x05,
-            0x00, 0x04, 0x30,
-        },
-        crypto.hash.sha2.Sha512 => [_]u8{
-            0x30, 0x51, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
-            0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, 0x05,
-            0x00, 0x04, 0x40,
-        },
-        else => @compileError("unreachable"),
-    };
-
-    var msg_hashed: [Hash.digest_length]u8 = undefined;
-    Hash.hash(message, &msg_hashed, .{});
-
     switch (modulus.len) {
         inline 128, 256, 384, 512 => |modulus_len| {
-            const ps_len = modulus_len - (hash_der.len + msg_hashed.len) - 3;
-            const em: [modulus_len]u8 =
-                [2]u8{ 0, 1 } ++
-                ([1]u8{0xff} ** ps_len) ++
-                [1]u8{0} ++
-                hash_der ++
-                msg_hashed;
-
-            const public_key = rsa.PublicKey.fromBytes(exponent, modulus) catch return error.CertificateSignatureInvalid;
-            const em_dec = rsa.encrypt(modulus_len, sig[0..modulus_len].*, public_key) catch |err| switch (err) {
-                error.MessageTooLong => unreachable,
-            };
-
-            if (!mem.eql(u8, &em, &em_dec)) {
+            const public_key = rsa.PublicKey.fromBytes(exponent, modulus) catch
+                return error.CertificateSignatureInvalid;
+            rsa.PKCS1v1_5Signature.verify(modulus_len, sig[0..modulus_len].*, msg, public_key, Hash) catch
                 return error.CertificateSignatureInvalid;
-            }
-        },
-        else => {
-            return error.CertificateSignatureUnsupportedBitCount;
         },
+        else => return error.CertificateSignatureUnsupportedBitCount,
     }
 }
 
@@ -908,9 +859,9 @@ pub const der = struct {
             pub const empty: Slice = .{ .start = 0, .end = 0 };
         };
 
-        pub const ParseElementError = error{CertificateFieldHasInvalidLength};
+        pub const ParseError = error{CertificateFieldHasInvalidLength};
 
-        pub fn parse(bytes: []const u8, index: u32) ParseElementError!Element {
+        pub fn parse(bytes: []const u8, index: u32) Element.ParseError!Element {
             var i = index;
             const identifier = @as(Identifier, @bitCast(bytes[i]));
             i += 1;
@@ -958,21 +909,41 @@ pub const rsa = struct {
     const Modulus = std.crypto.ff.Modulus(max_modulus_bits);
     const Fe = Modulus.Fe;
 
+    /// RFC 3447 8.1 RSASSA-PSS
     pub const PSSSignature = struct {
         pub fn fromBytes(comptime modulus_len: usize, msg: []const u8) [modulus_len]u8 {
-            var result = [1]u8{0} ** modulus_len;
-            std.mem.copyForwards(u8, &result, msg);
+            var result: [modulus_len]u8 = undefined;
+            @memcpy(result[0..msg.len], msg);
+            @memset(result[msg.len..], 0);
             return result;
         }
 
-        pub fn verify(comptime modulus_len: usize, sig: [modulus_len]u8, msg: []const u8, public_key: PublicKey, comptime Hash: type) !void {
+        pub const VerifyError = EncryptError || error{InvalidSignature};
+
+        pub fn verify(
+            comptime modulus_len: usize,
+            sig: [modulus_len]u8,
+            msg: []const u8,
+            public_key: PublicKey,
+            comptime Hash: type,
+        ) VerifyError!void {
+            try concatVerify(modulus_len, sig, &.{msg}, public_key, Hash);
+        }
+
+        pub fn concatVerify(
+            comptime modulus_len: usize,
+            sig: [modulus_len]u8,
+            msg: []const []const u8,
+            public_key: PublicKey,
+            comptime Hash: type,
+        ) VerifyError!void {
             const mod_bits = public_key.n.bits();
             const em_dec = try encrypt(modulus_len, sig, public_key);
 
-            EMSA_PSS_VERIFY(msg, &em_dec, mod_bits - 1, Hash.digest_length, Hash) catch unreachable;
+            try EMSA_PSS_VERIFY(msg, &em_dec, mod_bits - 1, Hash.digest_length, Hash);
         }
 
-        fn EMSA_PSS_VERIFY(msg: []const u8, em: []const u8, emBit: usize, sLen: usize, comptime Hash: type) !void {
+        fn EMSA_PSS_VERIFY(msg: []const []const u8, em: []const u8, emBit: usize, sLen: usize, comptime Hash: type) VerifyError!void {
             // 1.   If the length of M is greater than the input limitation for
             //      the hash function (2^61 - 1 octets for SHA-1), output
             //      "inconsistent" and stop.
@@ -986,7 +957,11 @@ pub const rsa = struct {
 
             // 2.   Let mHash = Hash(M), an octet string of length hLen.
             var mHash: [Hash.digest_length]u8 = undefined;
-            Hash.hash(msg, &mHash, .{});
+            {
+                var hasher: Hash = .init(.{});
+                for (msg) |part| hasher.update(part);
+                hasher.final(&mHash);
+            }
 
             // 3.   If emLen < hLen + sLen + 2, output "inconsistent" and stop.
             if (emLen < Hash.digest_length + sLen + 2) {
@@ -1082,25 +1057,14 @@ pub const rsa = struct {
         }
 
         fn MGF1(comptime Hash: type, out: []u8, seed: *const [Hash.digest_length]u8, len: usize) ![]u8 {
-            var counter: usize = 0;
+            var counter: u32 = 0;
             var idx: usize = 0;
-            var c: [4]u8 = undefined;
-            var hash: [Hash.digest_length + c.len]u8 = undefined;
-            @memcpy(hash[0..Hash.digest_length], seed);
-            var hashed: [Hash.digest_length]u8 = undefined;
+            var hash = seed.* ++ @as([4]u8, undefined);
 
             while (idx < len) {
-                c[0] = @as(u8, @intCast((counter >> 24) & 0xFF));
-                c[1] = @as(u8, @intCast((counter >> 16) & 0xFF));
-                c[2] = @as(u8, @intCast((counter >> 8) & 0xFF));
-                c[3] = @as(u8, @intCast(counter & 0xFF));
-
-                std.mem.copyForwards(u8, hash[seed.len..], &c);
-                Hash.hash(&hash, &hashed, .{});
-
-                std.mem.copyForwards(u8, out[idx..], &hashed);
-                idx += hashed.len;
-
+                std.mem.writeInt(u32, hash[seed.len..][0..4], counter, .big);
+                Hash.hash(&hash, out[idx..][0..Hash.digest_length], .{});
+                idx += Hash.digest_length;
                 counter += 1;
             }
 
@@ -1108,11 +1072,128 @@ pub const rsa = struct {
         }
     };
 
+    /// RFC 3447 8.2 RSASSA-PKCS1-v1_5
+    pub const PKCS1v1_5Signature = struct {
+        pub fn fromBytes(comptime modulus_len: usize, msg: []const u8) [modulus_len]u8 {
+            var result: [modulus_len]u8 = undefined;
+            @memcpy(result[0..msg.len], msg);
+            @memset(result[msg.len..], 0);
+            return result;
+        }
+
+        pub const VerifyError = EncryptError || error{InvalidSignature};
+
+        pub fn verify(
+            comptime modulus_len: usize,
+            sig: [modulus_len]u8,
+            msg: []const u8,
+            public_key: PublicKey,
+            comptime Hash: type,
+        ) VerifyError!void {
+            try concatVerify(modulus_len, sig, &.{msg}, public_key, Hash);
+        }
+
+        pub fn concatVerify(
+            comptime modulus_len: usize,
+            sig: [modulus_len]u8,
+            msg: []const []const u8,
+            public_key: PublicKey,
+            comptime Hash: type,
+        ) VerifyError!void {
+            const em_dec = try encrypt(modulus_len, sig, public_key);
+            const em = try EMSA_PKCS1_V1_5_ENCODE(msg, modulus_len, Hash);
+            if (!std.mem.eql(u8, &em_dec, &em)) return error.InvalidSignature;
+        }
+
+        fn EMSA_PKCS1_V1_5_ENCODE(msg: []const []const u8, comptime emLen: usize, comptime Hash: type) VerifyError![emLen]u8 {
+            comptime var em_index = emLen;
+            var em: [emLen]u8 = undefined;
+
+            // 1. Apply the hash function to the message M to produce a hash value
+            //    H:
+            //
+            //       H = Hash(M).
+            //
+            //    If the hash function outputs "message too long," output "message
+            //    too long" and stop.
+            var hasher: Hash = .init(.{});
+            for (msg) |part| hasher.update(part);
+            em_index -= Hash.digest_length;
+            hasher.final(em[em_index..]);
+
+            // 2. Encode the algorithm ID for the hash function and the hash value
+            //    into an ASN.1 value of type DigestInfo (see Appendix A.2.4) with
+            //    the Distinguished Encoding Rules (DER), where the type DigestInfo
+            //    has the syntax
+            //
+            //    DigestInfo ::= SEQUENCE {
+            //        digestAlgorithm AlgorithmIdentifier,
+            //        digest OCTET STRING
+            //    }
+            //
+            //    The first field identifies the hash function and the second
+            //    contains the hash value.  Let T be the DER encoding of the
+            //    DigestInfo value (see the notes below) and let tLen be the length
+            //    in octets of T.
+            const hash_der: []const u8 = &switch (Hash) {
+                crypto.hash.Sha1 => .{
+                    0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e,
+                    0x03, 0x02, 0x1a, 0x05, 0x00, 0x04, 0x14,
+                },
+                crypto.hash.sha2.Sha224 => .{
+                    0x30, 0x2d, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
+                    0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04, 0x05,
+                    0x00, 0x04, 0x1c,
+                },
+                crypto.hash.sha2.Sha256 => .{
+                    0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
+                    0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05,
+                    0x00, 0x04, 0x20,
+                },
+                crypto.hash.sha2.Sha384 => .{
+                    0x30, 0x41, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
+                    0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02, 0x05,
+                    0x00, 0x04, 0x30,
+                },
+                crypto.hash.sha2.Sha512 => .{
+                    0x30, 0x51, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
+                    0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, 0x05,
+                    0x00, 0x04, 0x40,
+                },
+                else => @compileError("unreachable"),
+            };
+            em_index -= hash_der.len;
+            @memcpy(em[em_index..][0..hash_der.len], hash_der);
+
+            // 3. If emLen < tLen + 11, output "intended encoded message length too
+            //    short" and stop.
+
+            // 4. Generate an octet string PS consisting of emLen - tLen - 3 octets
+            //    with hexadecimal value 0xff.  The length of PS will be at least 8
+            //    octets.
+            em_index -= 1;
+            @memset(em[2..em_index], 0xff);
+
+            // 5. Concatenate PS, the DER encoding T, and other padding to form the
+            //    encoded message EM as
+            //
+            //       EM = 0x00 || 0x01 || PS || 0x00 || T.
+            em[em_index] = 0x00;
+            em[1] = 0x01;
+            em[0] = 0x00;
+
+            // 6. Output EM.
+            return em;
+        }
+    };
+
     pub const PublicKey = struct {
         n: Modulus,
         e: Fe,
 
-        pub fn fromBytes(pub_bytes: []const u8, modulus_bytes: []const u8) !PublicKey {
+        pub const FromBytesError = error{CertificatePublicKeyInvalid};
+
+        pub fn fromBytes(pub_bytes: []const u8, modulus_bytes: []const u8) FromBytesError!PublicKey {
             // Reject modulus below 512 bits.
             // 512-bit RSA was factored in 1999, so this limit barely means anything,
             // but establish some limit now to ratchet in what we can.
@@ -1137,7 +1218,9 @@ pub const rsa = struct {
             };
         }
 
-        pub fn parseDer(pub_key: []const u8) !struct { modulus: []const u8, exponent: []const u8 } {
+        pub const ParseDerError = der.Element.ParseError || error{CertificateFieldHasWrongDataType};
+
+        pub fn parseDer(pub_key: []const u8) ParseDerError!struct { modulus: []const u8, exponent: []const u8 } {
             const pub_key_seq = try der.Element.parse(pub_key, 0);
             if (pub_key_seq.identifier.tag != .sequence) return error.CertificateFieldHasWrongDataType;
             const modulus_elem = try der.Element.parse(pub_key, pub_key_seq.slice.start);
@@ -1156,7 +1239,9 @@ pub const rsa = struct {
         }
     };
 
-    fn encrypt(comptime modulus_len: usize, msg: [modulus_len]u8, public_key: PublicKey) ![modulus_len]u8 {
+    const EncryptError = error{MessageTooLong};
+
+    fn encrypt(comptime modulus_len: usize, msg: [modulus_len]u8, public_key: PublicKey) EncryptError![modulus_len]u8 {
         const m = Fe.fromBytes(public_key.n, &msg, .big) catch return error.MessageTooLong;
         const e = public_key.n.powPublic(m, public_key.e) catch unreachable;
         var res: [modulus_len]u8 = undefined;
lib/std/crypto/ecdsa.zig
@@ -91,24 +91,33 @@ pub fn Ecdsa(comptime Curve: type, comptime Hash: type) type {
             s: Curve.scalar.CompressedScalar,
 
             /// Create a Verifier for incremental verification of a signature.
-            pub fn verifier(self: Signature, public_key: PublicKey) (NonCanonicalError || EncodingError || IdentityElementError)!Verifier {
-                return Verifier.init(self, public_key);
+            pub fn verifier(sig: Signature, public_key: PublicKey) Verifier.InitError!Verifier {
+                return Verifier.init(sig, public_key);
             }
 
+            pub const VerifyError = Verifier.InitError || Verifier.VerifyError;
+
             /// Verify the signature against a message and public key.
             /// Return IdentityElement or NonCanonical if the public key or signature are not in the expected range,
             /// or SignatureVerificationError if the signature is invalid for the given message and key.
-            pub fn verify(self: Signature, msg: []const u8, public_key: PublicKey) (IdentityElementError || NonCanonicalError || SignatureVerificationError)!void {
-                var st = try Verifier.init(self, public_key);
-                st.update(msg);
-                return st.verify();
+            pub fn verify(sig: Signature, msg: []const u8, public_key: PublicKey) VerifyError!void {
+                try sig.concatVerify(&.{msg}, public_key);
+            }
+
+            /// Verify the signature against a concatenated message and public key.
+            /// Return IdentityElement or NonCanonical if the public key or signature are not in the expected range,
+            /// or SignatureVerificationError if the signature is invalid for the given message and key.
+            pub fn concatVerify(sig: Signature, msg: []const []const u8, public_key: PublicKey) VerifyError!void {
+                var st = try Verifier.init(sig, public_key);
+                for (msg) |part| st.update(part);
+                try st.verify();
             }
 
             /// Return the raw signature (r, s) in big-endian format.
-            pub fn toBytes(self: Signature) [encoded_length]u8 {
+            pub fn toBytes(sig: Signature) [encoded_length]u8 {
                 var bytes: [encoded_length]u8 = undefined;
-                @memcpy(bytes[0 .. encoded_length / 2], &self.r);
-                @memcpy(bytes[encoded_length / 2 ..], &self.s);
+                @memcpy(bytes[0 .. encoded_length / 2], &sig.r);
+                @memcpy(bytes[encoded_length / 2 ..], &sig.s);
                 return bytes;
             }
 
@@ -124,23 +133,23 @@ pub fn Ecdsa(comptime Curve: type, comptime Hash: type) type {
             /// Encode the signature using the DER format.
             /// The maximum length of the DER encoding is der_encoded_length_max.
             /// The function returns a slice, that can be shorter than der_encoded_length_max.
-            pub fn toDer(self: Signature, buf: *[der_encoded_length_max]u8) []u8 {
+            pub fn toDer(sig: Signature, buf: *[der_encoded_length_max]u8) []u8 {
                 var fb = io.fixedBufferStream(buf);
                 const w = fb.writer();
-                const r_len = @as(u8, @intCast(self.r.len + (self.r[0] >> 7)));
-                const s_len = @as(u8, @intCast(self.s.len + (self.s[0] >> 7)));
+                const r_len = @as(u8, @intCast(sig.r.len + (sig.r[0] >> 7)));
+                const s_len = @as(u8, @intCast(sig.s.len + (sig.s[0] >> 7)));
                 const seq_len = @as(u8, @intCast(2 + r_len + 2 + s_len));
                 w.writeAll(&[_]u8{ 0x30, seq_len }) catch unreachable;
                 w.writeAll(&[_]u8{ 0x02, r_len }) catch unreachable;
-                if (self.r[0] >> 7 != 0) {
+                if (sig.r[0] >> 7 != 0) {
                     w.writeByte(0x00) catch unreachable;
                 }
-                w.writeAll(&self.r) catch unreachable;
+                w.writeAll(&sig.r) catch unreachable;
                 w.writeAll(&[_]u8{ 0x02, s_len }) catch unreachable;
-                if (self.s[0] >> 7 != 0) {
+                if (sig.s[0] >> 7 != 0) {
                     w.writeByte(0x00) catch unreachable;
                 }
-                w.writeAll(&self.s) catch unreachable;
+                w.writeAll(&sig.s) catch unreachable;
                 return fb.getWritten();
             }
 
@@ -236,7 +245,9 @@ pub fn Ecdsa(comptime Curve: type, comptime Hash: type) type {
             s: Curve.scalar.Scalar,
             public_key: PublicKey,
 
-            fn init(sig: Signature, public_key: PublicKey) (IdentityElementError || NonCanonicalError)!Verifier {
+            pub const InitError = IdentityElementError || NonCanonicalError;
+
+            fn init(sig: Signature, public_key: PublicKey) InitError!Verifier {
                 const r = try Curve.scalar.Scalar.fromBytes(sig.r, .big);
                 const s = try Curve.scalar.Scalar.fromBytes(sig.s, .big);
                 if (r.isZero() or s.isZero()) return error.IdentityElement;
@@ -254,8 +265,11 @@ pub fn Ecdsa(comptime Curve: type, comptime Hash: type) type {
                 self.h.update(data);
             }
 
+            pub const VerifyError = IdentityElementError || NonCanonicalError ||
+                SignatureVerificationError;
+
             /// Verify that the signature is valid for the entire message.
-            pub fn verify(self: *Verifier) (IdentityElementError || NonCanonicalError || SignatureVerificationError)!void {
+            pub fn verify(self: *Verifier) VerifyError!void {
                 const ht = Curve.scalar.encoded_length;
                 const h_len = @max(Hash.digest_length, ht);
                 var h: [h_len]u8 = [_]u8{0} ** h_len;
lib/std/crypto/tls.zig
@@ -54,6 +54,8 @@ pub const close_notify_alert = [_]u8{
 };
 
 pub const ProtocolVersion = enum(u16) {
+    tls_1_0 = 0x0301,
+    tls_1_1 = 0x0302,
     tls_1_2 = 0x0303,
     tls_1_3 = 0x0304,
     _,
@@ -69,14 +71,18 @@ pub const ContentType = enum(u8) {
 };
 
 pub const HandshakeType = enum(u8) {
+    hello_request = 0,
     client_hello = 1,
     server_hello = 2,
     new_session_ticket = 4,
     end_of_early_data = 5,
     encrypted_extensions = 8,
     certificate = 11,
+    server_key_exchange = 12,
     certificate_request = 13,
+    server_hello_done = 14,
     certificate_verify = 15,
+    client_key_exchange = 16,
     finished = 20,
     key_update = 24,
     message_hash = 254,
@@ -198,36 +204,36 @@ pub const AlertDescription = enum(u8) {
     _,
 
     pub fn toError(alert: AlertDescription) Error!void {
-        return switch (alert) {
+        switch (alert) {
             .close_notify => {}, // not an error
-            .unexpected_message => error.TlsAlertUnexpectedMessage,
-            .bad_record_mac => error.TlsAlertBadRecordMac,
-            .record_overflow => error.TlsAlertRecordOverflow,
-            .handshake_failure => error.TlsAlertHandshakeFailure,
-            .bad_certificate => error.TlsAlertBadCertificate,
-            .unsupported_certificate => error.TlsAlertUnsupportedCertificate,
-            .certificate_revoked => error.TlsAlertCertificateRevoked,
-            .certificate_expired => error.TlsAlertCertificateExpired,
-            .certificate_unknown => error.TlsAlertCertificateUnknown,
-            .illegal_parameter => error.TlsAlertIllegalParameter,
-            .unknown_ca => error.TlsAlertUnknownCa,
-            .access_denied => error.TlsAlertAccessDenied,
-            .decode_error => error.TlsAlertDecodeError,
-            .decrypt_error => error.TlsAlertDecryptError,
-            .protocol_version => error.TlsAlertProtocolVersion,
-            .insufficient_security => error.TlsAlertInsufficientSecurity,
-            .internal_error => error.TlsAlertInternalError,
-            .inappropriate_fallback => error.TlsAlertInappropriateFallback,
+            .unexpected_message => return error.TlsAlertUnexpectedMessage,
+            .bad_record_mac => return error.TlsAlertBadRecordMac,
+            .record_overflow => return error.TlsAlertRecordOverflow,
+            .handshake_failure => return error.TlsAlertHandshakeFailure,
+            .bad_certificate => return error.TlsAlertBadCertificate,
+            .unsupported_certificate => return error.TlsAlertUnsupportedCertificate,
+            .certificate_revoked => return error.TlsAlertCertificateRevoked,
+            .certificate_expired => return error.TlsAlertCertificateExpired,
+            .certificate_unknown => return error.TlsAlertCertificateUnknown,
+            .illegal_parameter => return error.TlsAlertIllegalParameter,
+            .unknown_ca => return error.TlsAlertUnknownCa,
+            .access_denied => return error.TlsAlertAccessDenied,
+            .decode_error => return error.TlsAlertDecodeError,
+            .decrypt_error => return error.TlsAlertDecryptError,
+            .protocol_version => return error.TlsAlertProtocolVersion,
+            .insufficient_security => return error.TlsAlertInsufficientSecurity,
+            .internal_error => return error.TlsAlertInternalError,
+            .inappropriate_fallback => return error.TlsAlertInappropriateFallback,
             .user_canceled => {}, // not an error
-            .missing_extension => error.TlsAlertMissingExtension,
-            .unsupported_extension => error.TlsAlertUnsupportedExtension,
-            .unrecognized_name => error.TlsAlertUnrecognizedName,
-            .bad_certificate_status_response => error.TlsAlertBadCertificateStatusResponse,
-            .unknown_psk_identity => error.TlsAlertUnknownPskIdentity,
-            .certificate_required => error.TlsAlertCertificateRequired,
-            .no_application_protocol => error.TlsAlertNoApplicationProtocol,
-            _ => error.TlsAlertUnknown,
-        };
+            .missing_extension => return error.TlsAlertMissingExtension,
+            .unsupported_extension => return error.TlsAlertUnsupportedExtension,
+            .unrecognized_name => return error.TlsAlertUnrecognizedName,
+            .bad_certificate_status_response => return error.TlsAlertBadCertificateStatusResponse,
+            .unknown_psk_identity => return error.TlsAlertUnknownPskIdentity,
+            .certificate_required => return error.TlsAlertCertificateRequired,
+            .no_application_protocol => return error.TlsAlertNoApplicationProtocol,
+            _ => return error.TlsAlertUnknown,
+        }
     }
 };
 
@@ -286,6 +292,20 @@ pub const NamedGroup = enum(u16) {
 };
 
 pub const CipherSuite = enum(u16) {
+    RSA_WITH_AES_128_CBC_SHA = 0x002F,
+    DHE_RSA_WITH_AES_128_CBC_SHA = 0x0033,
+    RSA_WITH_AES_256_CBC_SHA = 0x0035,
+    DHE_RSA_WITH_AES_256_CBC_SHA = 0x0039,
+    RSA_WITH_AES_128_CBC_SHA256 = 0x003C,
+    RSA_WITH_AES_256_CBC_SHA256 = 0x003D,
+    DHE_RSA_WITH_AES_128_CBC_SHA256 = 0x0067,
+    DHE_RSA_WITH_AES_256_CBC_SHA256 = 0x006B,
+    RSA_WITH_AES_128_GCM_SHA256 = 0x009C,
+    RSA_WITH_AES_256_GCM_SHA384 = 0x009D,
+    DHE_RSA_WITH_AES_128_GCM_SHA256 = 0x009E,
+    DHE_RSA_WITH_AES_256_GCM_SHA384 = 0x009F,
+    EMPTY_RENEGOTIATION_INFO_SCSV = 0x00FF,
+
     AES_128_GCM_SHA256 = 0x1301,
     AES_256_GCM_SHA384 = 0x1302,
     CHACHA20_POLY1305_SHA256 = 0x1303,
@@ -293,7 +313,98 @@ pub const CipherSuite = enum(u16) {
     AES_128_CCM_8_SHA256 = 0x1305,
     AEGIS_256_SHA512 = 0x1306,
     AEGIS_128L_SHA256 = 0x1307,
+
+    ECDHE_ECDSA_WITH_AES_128_CBC_SHA = 0xC009,
+    ECDHE_ECDSA_WITH_AES_256_CBC_SHA = 0xC00A,
+    ECDHE_RSA_WITH_AES_128_CBC_SHA = 0xC013,
+    ECDHE_RSA_WITH_AES_256_CBC_SHA = 0xC014,
+    ECDHE_ECDSA_WITH_AES_128_CBC_SHA256 = 0xC023,
+    ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 = 0xC024,
+    ECDHE_RSA_WITH_AES_128_CBC_SHA256 = 0xC027,
+    ECDHE_RSA_WITH_AES_256_CBC_SHA384 = 0xC028,
+    ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 = 0xC02B,
+    ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 = 0xC02C,
+    ECDHE_RSA_WITH_AES_128_GCM_SHA256 = 0xC02F,
+    ECDHE_RSA_WITH_AES_256_GCM_SHA384 = 0xC030,
+
+    ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 = 0xCCA8,
+    ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 = 0xCCA9,
+    DHE_RSA_WITH_CHACHA20_POLY1305_SHA256 = 0xCCAA,
+
     _,
+
+    pub const With = enum {
+        AES_128_CBC_SHA,
+        AES_256_CBC_SHA,
+        AES_128_CBC_SHA256,
+        AES_256_CBC_SHA256,
+        AES_256_CBC_SHA384,
+
+        AES_128_GCM_SHA256,
+        AES_256_GCM_SHA384,
+
+        CHACHA20_POLY1305_SHA256,
+
+        AES_128_CCM_SHA256,
+        AES_128_CCM_8_SHA256,
+
+        AEGIS_256_SHA512,
+        AEGIS_128L_SHA256,
+    };
+
+    pub fn with(cipher_suite: CipherSuite) With {
+        return switch (cipher_suite) {
+            .RSA_WITH_AES_128_CBC_SHA,
+            .DHE_RSA_WITH_AES_128_CBC_SHA,
+            .ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
+            .ECDHE_RSA_WITH_AES_128_CBC_SHA,
+            => .AES_128_CBC_SHA,
+            .RSA_WITH_AES_256_CBC_SHA,
+            .DHE_RSA_WITH_AES_256_CBC_SHA,
+            .ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
+            .ECDHE_RSA_WITH_AES_256_CBC_SHA,
+            => .AES_256_CBC_SHA,
+            .RSA_WITH_AES_128_CBC_SHA256,
+            .DHE_RSA_WITH_AES_128_CBC_SHA256,
+            .ECDHE_ECDSA_WITH_AES_128_CBC_SHA256,
+            .ECDHE_RSA_WITH_AES_128_CBC_SHA256,
+            => .AES_128_CBC_SHA256,
+            .RSA_WITH_AES_256_CBC_SHA256,
+            .DHE_RSA_WITH_AES_256_CBC_SHA256,
+            => .AES_256_CBC_SHA256,
+            .ECDHE_ECDSA_WITH_AES_256_CBC_SHA384,
+            .ECDHE_RSA_WITH_AES_256_CBC_SHA384,
+            => .AES_256_CBC_SHA384,
+
+            .RSA_WITH_AES_128_GCM_SHA256,
+            .DHE_RSA_WITH_AES_128_GCM_SHA256,
+            .AES_128_GCM_SHA256,
+            .ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
+            .ECDHE_RSA_WITH_AES_128_GCM_SHA256,
+            => .AES_128_GCM_SHA256,
+            .RSA_WITH_AES_256_GCM_SHA384,
+            .DHE_RSA_WITH_AES_256_GCM_SHA384,
+            .AES_256_GCM_SHA384,
+            .ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
+            .ECDHE_RSA_WITH_AES_256_GCM_SHA384,
+            => .AES_256_GCM_SHA384,
+
+            .CHACHA20_POLY1305_SHA256,
+            .ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
+            .ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,
+            .DHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
+            => .CHACHA20_POLY1305_SHA256,
+
+            .AES_128_CCM_SHA256 => .AES_128_CCM_SHA256,
+            .AES_128_CCM_8_SHA256 => .AES_128_CCM_8_SHA256,
+
+            .AEGIS_256_SHA512 => .AEGIS_256_SHA512,
+            .AEGIS_128L_SHA256 => .AEGIS_128L_SHA256,
+
+            .EMPTY_RENEGOTIATION_INFO_SCSV => unreachable,
+            _ => unreachable,
+        };
+    }
 };
 
 pub const CertificateType = enum(u8) {
@@ -308,58 +419,108 @@ pub const KeyUpdateRequest = enum(u8) {
     _,
 };
 
-pub fn HandshakeCipherT(comptime AeadType: type, comptime HashType: type) type {
+pub fn HandshakeCipherT(comptime AeadType: type, comptime HashType: type, comptime explicit_iv_length: comptime_int) type {
     return struct {
-        pub const AEAD = AeadType;
-        pub const Hash = HashType;
-        pub const Hmac = crypto.auth.hmac.Hmac(Hash);
-        pub const Hkdf = crypto.kdf.hkdf.Hkdf(Hmac);
+        pub const A = ApplicationCipherT(AeadType, HashType, explicit_iv_length);
 
-        handshake_secret: [Hkdf.prk_length]u8,
-        master_secret: [Hkdf.prk_length]u8,
-        client_handshake_key: [AEAD.key_length]u8,
-        server_handshake_key: [AEAD.key_length]u8,
-        client_finished_key: [Hmac.key_length]u8,
-        server_finished_key: [Hmac.key_length]u8,
-        client_handshake_iv: [AEAD.nonce_length]u8,
-        server_handshake_iv: [AEAD.nonce_length]u8,
-        transcript_hash: Hash,
+        transcript_hash: A.Hash,
+        version: union {
+            tls_1_2: struct {
+                server_verify_data: [12]u8,
+                app_cipher: A.Tls_1_2,
+            },
+            tls_1_3: struct {
+                handshake_secret: [A.Hkdf.prk_length]u8,
+                master_secret: [A.Hkdf.prk_length]u8,
+                client_handshake_key: [A.AEAD.key_length]u8,
+                server_handshake_key: [A.AEAD.key_length]u8,
+                client_finished_key: [A.Hmac.key_length]u8,
+                server_finished_key: [A.Hmac.key_length]u8,
+                client_handshake_iv: [A.AEAD.nonce_length]u8,
+                server_handshake_iv: [A.AEAD.nonce_length]u8,
+            },
+        },
     };
 }
 
 pub const HandshakeCipher = union(enum) {
-    AES_128_GCM_SHA256: HandshakeCipherT(crypto.aead.aes_gcm.Aes128Gcm, crypto.hash.sha2.Sha256),
-    AES_256_GCM_SHA384: HandshakeCipherT(crypto.aead.aes_gcm.Aes256Gcm, crypto.hash.sha2.Sha384),
-    CHACHA20_POLY1305_SHA256: HandshakeCipherT(crypto.aead.chacha_poly.ChaCha20Poly1305, crypto.hash.sha2.Sha256),
-    AEGIS_256_SHA512: HandshakeCipherT(crypto.aead.aegis.Aegis256, crypto.hash.sha2.Sha512),
-    AEGIS_128L_SHA256: HandshakeCipherT(crypto.aead.aegis.Aegis128L, crypto.hash.sha2.Sha256),
+    AES_128_GCM_SHA256: HandshakeCipherT(crypto.aead.aes_gcm.Aes128Gcm, crypto.hash.sha2.Sha256, 8),
+    AES_256_GCM_SHA384: HandshakeCipherT(crypto.aead.aes_gcm.Aes256Gcm, crypto.hash.sha2.Sha384, 8),
+    CHACHA20_POLY1305_SHA256: HandshakeCipherT(crypto.aead.chacha_poly.ChaCha20Poly1305, crypto.hash.sha2.Sha256, 0),
+    AEGIS_256_SHA512: HandshakeCipherT(crypto.aead.aegis.Aegis256, crypto.hash.sha2.Sha512, 0),
+    AEGIS_128L_SHA256: HandshakeCipherT(crypto.aead.aegis.Aegis128L, crypto.hash.sha2.Sha256, 0),
 };
 
-pub fn ApplicationCipherT(comptime AeadType: type, comptime HashType: type) type {
-    return struct {
+pub fn ApplicationCipherT(comptime AeadType: type, comptime HashType: type, comptime explicit_iv_length: comptime_int) type {
+    return union {
         pub const AEAD = AeadType;
         pub const Hash = HashType;
         pub const Hmac = crypto.auth.hmac.Hmac(Hash);
         pub const Hkdf = crypto.kdf.hkdf.Hkdf(Hmac);
 
-        client_secret: [Hash.digest_length]u8,
-        server_secret: [Hash.digest_length]u8,
-        client_key: [AEAD.key_length]u8,
-        server_key: [AEAD.key_length]u8,
-        client_iv: [AEAD.nonce_length]u8,
-        server_iv: [AEAD.nonce_length]u8,
+        pub const enc_key_length = AEAD.key_length;
+        pub const fixed_iv_length = AEAD.nonce_length - explicit_iv_length;
+        pub const record_iv_length = explicit_iv_length;
+        pub const mac_length = AEAD.tag_length;
+        pub const mac_key_length = Hmac.key_length_min;
+
+        tls_1_2: Tls_1_2,
+        tls_1_3: Tls_1_3,
+
+        pub const Tls_1_2 = extern struct {
+            client_write_MAC_key: [mac_key_length]u8,
+            server_write_MAC_key: [mac_key_length]u8,
+            client_write_key: [enc_key_length]u8,
+            server_write_key: [enc_key_length]u8,
+            client_write_IV: [fixed_iv_length]u8,
+            server_write_IV: [fixed_iv_length]u8,
+            // non-standard entropy
+            client_salt: [record_iv_length]u8,
+        };
+
+        pub const Tls_1_3 = struct {
+            client_secret: [Hash.digest_length]u8,
+            server_secret: [Hash.digest_length]u8,
+            client_key: [AEAD.key_length]u8,
+            server_key: [AEAD.key_length]u8,
+            client_iv: [AEAD.nonce_length]u8,
+            server_iv: [AEAD.nonce_length]u8,
+        };
     };
 }
 
 /// Encryption parameters for application traffic.
 pub const ApplicationCipher = union(enum) {
-    AES_128_GCM_SHA256: ApplicationCipherT(crypto.aead.aes_gcm.Aes128Gcm, crypto.hash.sha2.Sha256),
-    AES_256_GCM_SHA384: ApplicationCipherT(crypto.aead.aes_gcm.Aes256Gcm, crypto.hash.sha2.Sha384),
-    CHACHA20_POLY1305_SHA256: ApplicationCipherT(crypto.aead.chacha_poly.ChaCha20Poly1305, crypto.hash.sha2.Sha256),
-    AEGIS_256_SHA512: ApplicationCipherT(crypto.aead.aegis.Aegis256, crypto.hash.sha2.Sha512),
-    AEGIS_128L_SHA256: ApplicationCipherT(crypto.aead.aegis.Aegis128L, crypto.hash.sha2.Sha256),
+    AES_128_GCM_SHA256: ApplicationCipherT(crypto.aead.aes_gcm.Aes128Gcm, crypto.hash.sha2.Sha256, 8),
+    AES_256_GCM_SHA384: ApplicationCipherT(crypto.aead.aes_gcm.Aes256Gcm, crypto.hash.sha2.Sha384, 8),
+    CHACHA20_POLY1305_SHA256: ApplicationCipherT(crypto.aead.chacha_poly.ChaCha20Poly1305, crypto.hash.sha2.Sha256, 0),
+    AEGIS_256_SHA512: ApplicationCipherT(crypto.aead.aegis.Aegis256, crypto.hash.sha2.Sha512, 0),
+    AEGIS_128L_SHA256: ApplicationCipherT(crypto.aead.aegis.Aegis128L, crypto.hash.sha2.Sha256, 0),
 };
 
+pub fn hmacExpandLabel(
+    comptime Hmac: type,
+    secret: []const u8,
+    label_then_seed: []const []const u8,
+    comptime len: usize,
+) [len]u8 {
+    const initial_hmac: Hmac = .init(secret);
+    var a: [Hmac.mac_length]u8 = undefined;
+    var result: [std.mem.alignForwardAnyAlign(usize, len, Hmac.mac_length)]u8 = undefined;
+    var index: usize = 0;
+    while (index < result.len) : (index += Hmac.mac_length) {
+        var a_hmac = initial_hmac;
+        if (index > 0) a_hmac.update(&a) else for (label_then_seed) |part| a_hmac.update(part);
+        a_hmac.final(&a);
+
+        var result_hmac = initial_hmac;
+        result_hmac.update(&a);
+        for (label_then_seed) |part| result_hmac.update(part);
+        result_hmac.final(result[index..][0..Hmac.mac_length]);
+    }
+    return result[0..len].*;
+}
+
 pub fn hkdfExpandLabel(
     comptime Hkdf: type,
     key: [Hkdf.prk_length]u8,
@@ -418,19 +579,16 @@ pub inline fn enum_array(comptime E: type, comptime tags: []const E) [2 + @sizeO
     return array(2, result);
 }
 
-pub inline fn int2(x: u16) [2]u8 {
-    return .{
-        @as(u8, @truncate(x >> 8)),
-        @as(u8, @truncate(x)),
-    };
+pub inline fn int2(int: u16) [2]u8 {
+    var arr: [2]u8 = undefined;
+    std.mem.writeInt(u16, &arr, int, .big);
+    return arr;
 }
 
-pub inline fn int3(x: u24) [3]u8 {
-    return .{
-        @as(u8, @truncate(x >> 16)),
-        @as(u8, @truncate(x >> 8)),
-        @as(u8, @truncate(x)),
-    };
+pub inline fn int3(int: u24) [3]u8 {
+    var arr: [3]u8 = undefined;
+    std.mem.writeInt(u24, &arr, int, .big);
+    return arr;
 }
 
 /// An abstraction to ensure that protocol-parsing code does not perform an
lib/std/http/protocol.zig
@@ -172,7 +172,13 @@ pub const HeadersParser = struct {
                     const data_avail = r.next_chunk_length;
 
                     if (skip) {
-                        try conn.fill();
+                        conn.fill() catch |err| switch (err) {
+                            error.EndOfStream => {
+                                r.done = true;
+                                return 0;
+                            },
+                            else => |e| return e,
+                        };
 
                         const nread = @min(conn.peek().len, data_avail);
                         conn.drop(@intCast(nread));
@@ -196,7 +202,13 @@ pub const HeadersParser = struct {
                     }
                 },
                 .chunk_data_suffix, .chunk_data_suffix_r, .chunk_head_size, .chunk_head_ext, .chunk_head_r => {
-                    try conn.fill();
+                    conn.fill() catch |err| switch (err) {
+                        error.EndOfStream => {
+                            r.done = true;
+                            return 0;
+                        },
+                        else => |e| return e,
+                    };
 
                     const i = r.findChunkedLen(conn.peek());
                     conn.drop(@intCast(i));
@@ -226,7 +238,13 @@ pub const HeadersParser = struct {
                     const out_avail = buffer.len - out_index;
 
                     if (skip) {
-                        try conn.fill();
+                        conn.fill() catch |err| switch (err) {
+                            error.EndOfStream => {
+                                r.done = true;
+                                return 0;
+                            },
+                            else => |e| return e,
+                        };
 
                         const nread = @min(conn.peek().len, data_avail);
                         conn.drop(@intCast(nread));