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Refactored s check and improved failure in recover_public_key. #9142

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Merged
orizi merged 1 commit into from
Dec 17, 2025
Merged

Refactored s check and improved failure in recover_public_key. #9142

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15 changes: 11 additions & 4 deletions corelib/src/ecdsa.cairo
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
}

Expand Down Expand Up @@ -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()?;

Expand Down Expand Up @@ -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.
///
Expand Down
33 changes: 25 additions & 8 deletions corelib/src/test/ec_test.cairo
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Original file line number Diff line number Diff line change
@@ -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;
Expand Down Expand Up @@ -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(
Expand All @@ -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,
);
}

Expand Down