Commit cd8f0aa4ca174ae1d43232d20f27120bcd74e71f | zig

author	Frank Denis <124872+jedisct1@users.noreply.github.com> 2026-01-07 23:02:46+01:00
committer	Frank Denis <124872+jedisct1@users.noreply.github.com> 2026-01-07 23:02:46+01:00
log	cd8f0aa4ca174ae1d43232d20f27120bcd74e71f
tree	9dcc966ce483e3561768845514fccf2d822a831b
parent	22380c78b1f9fd714ea6c89d2b902846ccf2e4f9

Add signerWithBaseNonce

1 files changed, 22 insertions(+), 9 deletions(-)

lib
- std
  - crypto
    25519
    ed25519.zig

lib/std/crypto/25519/ed25519.zig+22-9

 @@ -385,24 +385,23 @@ pub const Ed25519 = struct {
             );
         }
-        /// Create a Signer, that can be used for incremental signing.
+        /// Create a signer that can be used for incremental signing, using a custom base nonce.
-        /// Note that the signature is not deterministic.
+        /// `base_nonce` must be unique for each signed message; otherwise, the secret key can
-        pub fn signer(
+        /// be trivially recovered by an attacker.
+        /// It can be generated using a cryptographically secure random number generator.
+        pub fn signerWithBaseNonce(
             key_pair: KeyPair,
-            /// If set, should be something unique for each message, such as a
+            base_nonce: [32]u8,
-            /// random nonce, or a counter.
+            /// If set, should be something unique for each message, such as a counter.
             noise: ?[noise_length]u8,
-            io: std.Io,
         ) (IdentityElementError || KeyMismatchError || NonCanonicalError || WeakPublicKeyError)!Signer {
             if (!mem.eql(u8, &key_pair.secret_key.publicKeyBytes(), &key_pair.public_key.toBytes())) {
                 return error.KeyMismatch;
             }
             const scalar_and_prefix = key_pair.secret_key.scalarAndPrefix();
-            var entropy: [noise_length]u8 = undefined;
-            io.random(&entropy);
             var h = Sha512.init(.{});
             h.update(&scalar_and_prefix.prefix);
-            h.update(&entropy);
+            h.update(&base_nonce);
             if (noise) |*z| {
                 h.update(z);
             }
 @@ -412,6 +411,20 @@ pub const Ed25519 = struct {
             return Signer.init(scalar_and_prefix.scalar, nonce, key_pair.public_key);
         }
+        /// Create a Signer, that can be used for incremental signing.
+        /// Note that the signature is not deterministic.
+        pub fn signer(
+            key_pair: KeyPair,
+            /// If set, should be something unique for each message, such as a
+            /// random nonce, or a counter.
+            noise: ?[noise_length]u8,
+            io: std.Io,
+        ) (IdentityElementError || KeyMismatchError || NonCanonicalError || WeakPublicKeyError)!Signer {
+            var base_nonce: [32]u8 = undefined;
+            io.random(&base_nonce);
+            return key_pair.signerWithBaseNonce(base_nonce, noise);
+        }
     };
     /// A (signature, message, public_key) tuple for batch verification