Commit 26793453a7

Frank Denis <github@pureftpd.org>
2020-10-26 13:23:16
std/crypto/blake2b: allow the initial output length to be set
BLAKE2 includes the expected output length in the initial state. This length is actually distinct from the actual output length used at finalization. BLAKE2b-256/128 is thus not the same as BLAKE2b-128. This behavior can be a little bit surprising, and has been "fixed" in BLAKE3. In order to support this, we may want to provide an option to set the length used for domain separation. In Zig, there is another reason to allow this: we assume that the output length is defined at comptime. But BLAKE2 doesn't have a fixed output length. For an output length that is not known at comptime, we can't take the full block size and truncate it due to the reason above. What we can do now is set that length as an option to get the correct initial state, and truncate the output if necessary.
master
1 parent 32e65c3
Changed files (1)
lib
std
crypto
blake2.zig
lib/std/crypto/blake2.zig
@@ -44,7 +44,7 @@ pub fn Blake2s(comptime out_bits: usize) type {
         pub const key_length_min = 0;
         pub const key_length_max = 32;
         pub const key_length = 32; // recommended key length
-        pub const Options = struct { key: ?[]const u8 = null, salt: ?[8]u8 = null, context: ?[8]u8 = null };
+        pub const Options = struct { key: ?[]const u8 = null, salt: ?[8]u8 = null, context: ?[8]u8 = null, expected_out_bits: usize = out_bits };
 
         const iv = [8]u32{
             0x6A09E667,
@@ -84,7 +84,7 @@ pub fn Blake2s(comptime out_bits: usize) type {
 
             const key_len = if (options.key) |key| key.len else 0;
             // default parameters
-            d.h[0] ^= 0x01010000 ^ @truncate(u32, key_len << 8) ^ @intCast(u32, out_bits >> 3);
+            d.h[0] ^= 0x01010000 ^ @truncate(u32, key_len << 8) ^ @intCast(u32, options.expected_out_bits >> 3);
             d.t = 0;
             d.buf_len = 0;
 
@@ -385,7 +385,7 @@ pub fn Blake2b(comptime out_bits: usize) type {
         pub const key_length_min = 0;
         pub const key_length_max = 64;
         pub const key_length = 32; // recommended key length
-        pub const Options = struct { key: ?[]const u8 = null, salt: ?[16]u8 = null, context: ?[16]u8 = null };
+        pub const Options = struct { key: ?[]const u8 = null, salt: ?[16]u8 = null, context: ?[16]u8 = null, expected_out_bits: usize = out_bits };
 
         const iv = [8]u64{
             0x6a09e667f3bcc908,
@@ -427,7 +427,7 @@ pub fn Blake2b(comptime out_bits: usize) type {
 
             const key_len = if (options.key) |key| key.len else 0;
             // default parameters
-            d.h[0] ^= 0x01010000 ^ (key_len << 8) ^ (out_bits >> 3);
+            d.h[0] ^= 0x01010000 ^ (key_len << 8) ^ (options.expected_out_bits >> 3);
             d.t = 0;
             d.buf_len = 0;