Snezhkko
diff --git a/‎corelib/src/ecdsa.cairo‎
Lines changed: 11 additions & 4 deletions b/‎corelib/src/ecdsa.cairo‎
Lines changed: 11 additions & 4 deletions
diff --git a/‎corelib/src/test/ec_test.cairo‎
Lines changed: 25 additions & 8 deletions b/‎corelib/src/test/ec_test.cairo‎
Lines changed: 25 additions & 8 deletions
@@ -55,10 +55,7 @@ use crate::zeroable::IsZeroResult;
 pub fn check_ecdsa_signature(
     message_hash: felt252, public_key: felt252, signature_r: felt252, signature_s: felt252,
 ) -> bool {
-    // Check that s != 0 (mod stark_curve::ORDER).
-    if signature_s == 0
-        || signature_s == ec::stark_curve::ORDER
-        || signature_r == ec::stark_curve::ORDER {
+    if is_equivalent_to_zero(signature_s) || signature_r == ec::stark_curve::ORDER {
         return false;
     }
 
@@ -158,6 +155,10 @@ pub fn check_ecdsa_signature(
 pub fn recover_public_key(
     message_hash: felt252, signature_r: felt252, signature_s: felt252, y_parity: bool,
 ) -> Option<felt252> {
+    if is_equivalent_to_zero(signature_s) {
+        return None;
+    }
+
     let r_point = EcPointTrait::new_nz_from_x(signature_r)?;
     let gen_point = generator_point()?;
 
@@ -196,6 +197,12 @@ pub fn recover_public_key(
     Some(state.finalize_nz()?.x())
 }
 
+/// Checks if `value != 0` (mod stark_curve::ORDER).
+fn is_equivalent_to_zero(value: felt252) -> bool {
+    // Note that `2 * ec::stark_curve::ORDER` is larger than the felt252 PRIME.
+    value == 0 || value == ec::stark_curve::ORDER
+}
+
 // TODO(orizi): Remove this function on next Sierra release.
 /// Returns the generator point of the elliptic curve.
 ///
 
@@ -1,4 +1,4 @@
-use crate::ec::{EcPoint, EcPointTrait, EcStateTrait};
+use crate::ec::{EcPoint, EcPointTrait, EcStateTrait, stark_curve};
 use crate::ecdsa;
 use crate::option::OptionTrait;
 use crate::test::test_utils::assert_eq;
@@ -116,13 +116,11 @@ fn test_ecdsa_recover_public_key() {
     let message_hash = 0x503f4bea29baee10b22a7f10bdc82dda071c977c1f25b8f3973d34e6b03b2c;
     let signature_r = 0xbe96d72eb4f94078192c2e84d5230cde2a70f4b45c8797e2c907acff5060bb;
     let signature_s = 0x677ae6bba6daf00d2631fab14c8acf24be6579f9d9e98f67aa7f2770e57a1f5;
-    assert_eq(
-        @ecdsa::recover_public_key(:message_hash, :signature_r, :signature_s, y_parity: false)
-            .unwrap(),
-        @0x7b7454acbe7845da996377f85eb0892044d75ae95d04d3325a391951f35d2ec,
-        'recover_ecdsa_public_key failed',
+    assert_eq!(
+        ecdsa::recover_public_key(:message_hash, :signature_r, :signature_s, y_parity: false),
+        Some(0x7b7454acbe7845da996377f85eb0892044d75ae95d04d3325a391951f35d2ec),
     );
-    assert(
+    assert!(
         ecdsa::check_ecdsa_signature(
             :message_hash,
             public_key: ecdsa::recover_public_key(
@@ -132,7 +130,26 @@ fn test_ecdsa_recover_public_key() {
             :signature_r,
             :signature_s,
         ),
-        'ecdsa returned false',
+    );
+    assert_eq!(
+        ecdsa::recover_public_key(:message_hash, signature_r: 0, :signature_s, y_parity: true),
+        None,
+    );
+    assert_eq!(
+        ecdsa::recover_public_key(
+            :message_hash, signature_r: stark_curve::ORDER, :signature_s, y_parity: true,
+        ),
+        None,
+    );
+    assert_eq!(
+        ecdsa::recover_public_key(:message_hash, :signature_r, signature_s: 0, y_parity: true),
+        None,
+    );
+    assert_eq!(
+        ecdsa::recover_public_key(
+            :message_hash, :signature_r, signature_s: stark_curve::ORDER, y_parity: true,
+        ),
+        None,
     );
 }