zig

commit cd8f0aa4ca174ae1d43232d20f27120bcd74e71f (tree)
parent 22380c78b1f9fd714ea6c89d2b902846ccf2e4f9
Author: Frank Denis <github@pureftpd.org>
Date:   Wed,  7 Jan 2026 23:02:46 +0100

Add signerWithBaseNonce

Diffstat:
M
lib/std/crypto/25519/ed25519.zig
 | 
31
++++++++++++++++++++++---------

1 file changed, 22 insertions(+), 9 deletions(-)
diff --git a/lib/std/crypto/25519/ed25519.zig b/lib/std/crypto/25519/ed25519.zig
@@ -385,24 +385,23 @@ pub const Ed25519 = struct {
             );
         }
 
-        /// Create a Signer, that can be used for incremental signing.
-        /// Note that the signature is not deterministic.
-        pub fn signer(
+        /// Create a signer that can be used for incremental signing, using a custom base nonce.
+        /// `base_nonce` must be unique for each signed message; otherwise, the secret key can
+        /// 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
-            /// random nonce, or a counter.
+            base_nonce: [32]u8,
+            /// 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