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fix(StdSecp256k1): reject non-canonical coordinates in isOnCurve #928

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Merged
mattsse merged 3 commits into from
Oct 23, 2026
Merged

fix(StdSecp256k1): reject non-canonical coordinates in isOnCurve #928

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1dcf0a1
fix(StdSecp256k1): reject non-canonical coordinates in isOnCurve
ara-stock Oct 9, 2026
7ceb3ac
Merge branch 'master' into fix/secp256k1-is-on-curve-canonical
mattsse Oct 23, 2026
76f1223
Merge branch 'master' into fix/secp256k1-is-on-curve-canonical
mattsse Oct 23, 2026
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5 changes: 3 additions & 2 deletions src/StdSecp256k1.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -65,11 +65,12 @@ library StdSecp256k1 {
return (GX, GY, 1);
}

/// @notice Returns whether the affine point `(x, y)` is on the curve `y² ≡ x³ + 7 (mod P)`.
/// @notice Returns whether the affine point `(x, y)` is on the curve `y² ≡ x³ + 7 (mod P)`
/// with `x` and `y` in `[0, P)`.
/// @dev Uses `mulmod`/`addmod` for field arithmetic.
function isOnCurve(uint256 x, uint256 y) internal pure returns (bool) {
// https://github.com/ethereum/go-ethereum/blob/v1.17.5/crypto/secp256k1/curve.go#L75
return mulmod(y, y, P) == addmod(mulmod(x, mulmod(x, x, P), P), B, P);
return x < P && y < P && mulmod(y, y, P) == addmod(mulmod(x, mulmod(x, x, P), P), B, P);
}

/// @notice Returns whether `scalar` is canonically valid (`scalar` in `[0, N)`).
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12 changes: 12 additions & 0 deletions test/StdSecp256k1.t.sol
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Expand Up @@ -53,6 +53,18 @@ contract StdSecp256k1Test is Test {
assertFalse(StdSecp256k1.isIdentityProjective(projectiveX, projectiveY, z));
}

function test_IsOnCurveRejectsNonCanonicalCoordinates() external pure {
uint256 x1 = 1;
uint256 y1 = 0x4218F20AE6C646B363DB68605822FB14264CA8D2587FDD6FBC750D587E76A7EE;
assertTrue(StdSecp256k1.isOnCurve(x1, y1));
assertFalse(StdSecp256k1.isOnCurve(x1 + StdSecp256k1.P, y1));

uint256 x2 = 0x1FE1E5EF3FCEB5C135AB7741333CE5A6E80D68167653F6B2B24BCBCFAAAFF507;
uint256 y2 = 1;
assertTrue(StdSecp256k1.isOnCurve(x2, y2));
assertFalse(StdSecp256k1.isOnCurve(x2, y2 + StdSecp256k1.P));
}

function test_ScalarBounds() external pure {
assertTrue(StdSecp256k1.isValidScalar(0));
assertFalse(StdSecp256k1.isValidNonZeroScalar(0));
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