fix: allow secp256k1-recover? to accept high-S signatures

Author: obycode

clarity/src/vm/tests/crypto.rs

@@ -49,6 +49,29 @@ fn zeroed_buff_literal(len: usize) -> String {
     buff_literal(&vec![0u8; len])
 }
 
+#[test]
+fn test_secp256k1_recover_accepts_high_s_signature() {
+    let message = "0x7147f89f7ba4980c8628b52c2f0351f018ed31ba593e5ed676ad428c67c23ffb";
+    let signature = "0xe120eaed297a125259ee235a702c3f8dc18f8e65cdb28625061dd9e80197b0e6d29c9b9a200ecffee51033a93c896e9e00907789888eef42f3ede3a81dd7730201";
+    let expected_pubkey = "0x034170a2083dccbc2be253885a8d0e9f7ce859eb370d0c5cae3b6994af4cb9d666";
+    let fallback = zeroed_buff_literal(33);
+    let program = format!(
+        "(is-eq (unwrap! (secp256k1-recover? {message} {signature}) {fallback}) {expected_pubkey})"
+    );
+
+    assert_eq!(
+        Value::Bool(true),
+        execute_with_parameters(
+            program.as_str(),
+            ClarityVersion::Clarity1,
+            StacksEpochId::Epoch20,
+            false
+        )
+        .expect("execution should succeed")
+        .expect("should return a value")
+    );
+}
+
 #[test]
 fn test_secp256r1_verify_valid_signature_returns_true() {
     let (message, signature, pubkey) = secp256r1_vectors();

stacks-common/src/util/secp256k1.rs

@@ -475,14 +475,25 @@ pub fn secp256k1_recover(
         return Err(Secp256k1Error::InvalidSignature);
     }
 
-    let recovery_id = K256RecoveryId::from_byte(serialized_signature_arr[64])
+    let mut recovery_id = K256RecoveryId::from_byte(serialized_signature_arr[64])
         .ok_or(Secp256k1Error::InvalidRecoveryId)?;
 
     let signature = K256Signature::from_slice(&serialized_signature_arr[..64])
         .map_err(|_| Secp256k1Error::InvalidSignature)?;
 
+    let normalized_signature = signature.normalize_s();
+
+    let signature_ref: &K256Signature = if let Some(normalized) = normalized_signature.as_ref() {
+        let flipped_recovery_id =
+            K256RecoveryId::new(!recovery_id.is_y_odd(), recovery_id.is_x_reduced());
+        recovery_id = flipped_recovery_id;
+        normalized
+    } else {
+        &signature
+    };
+
     let recovered_pub =
-        K256VerifyingKey::recover_from_prehash(message_arr, &signature, recovery_id)
+        K256VerifyingKey::recover_from_prehash(message_arr, signature_ref, recovery_id)
             .map_err(|_| Secp256k1Error::RecoveryFailed)?;
 
     let public_key = K256PublicKey::from(&recovered_pub);