zig

commit b8a77f3d5931e0bf4f3c5544957dd36380367a43 (tree)
parent d4e22e3eb668968fa30f25c382b97629902f0bf8
Author: Frank Denis <124872+jedisct1@users.noreply.github.com>
Date:   Thu, 22 Jul 2021 01:27:42 +0200

std.crypto: handle the top bit in 25519.field.fromBytes64() (#9435)

The only known use case for this is the hash-to-curve operation where the top bit is always cleared.

But the function is public, so let's make it work as one would expect in the general case.

Also fix the comment by the way.
Diffstat:
M
lib/std/crypto/25519/field.zig
 | 
4
++--

1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/lib/std/crypto/25519/field.zig b/lib/std/crypto/25519/field.zig
@@ -93,7 +93,7 @@ pub const Fe = struct {
         return s;
     }
 
-    /// Map a 64-bit big endian string into a field element
+    /// Map a 64 bytes big endian string into a field element
     pub fn fromBytes64(s: [64]u8) Fe {
         var fl: [32]u8 = undefined;
         var gl: [32]u8 = undefined;
@@ -106,7 +106,7 @@ pub const Fe = struct {
         gl[31] &= 0x7f;
         var fe_f = fromBytes(fl);
         const fe_g = fromBytes(gl);
-        fe_f.limbs[0] += (s[32] >> 7) * 19;
+        fe_f.limbs[0] += (s[32] >> 7) * 19 + @as(u10, s[0] >> 7) * 722;
         i = 0;
         while (i < 5) : (i += 1) {
             fe_f.limbs[i] += 38 * fe_g.limbs[i];