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Reject public keys that are not on the curve in the builtin ECDH #1000

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Merged
zxzxwu merged 1 commit into from
Oct 5, 2026
Merged

Reject public keys that are not on the curve in the builtin ECDH #1000

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3 changes: 3 additions & 0 deletions bumble/crypto/builtin.py
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Original file line number Diff line number Diff line change
Expand Up @@ -572,6 +572,9 @@ def generate_public_key(self, private_key: int) -> _Point:

def ecdh_shared_secret(self, private_key: int, other_public_key: _Point) -> bytes:
"""Computes the shared secret using ECDH."""
x, y = other_public_key.x, other_public_key.y
if (y * y - (x * x * x + self.a * x + self.b)) % self.p != 0:
raise core.InvalidPacketError("Public key is not a point on the curve")
other_public_key_jacobian = _JacobianPoint.from_affine(other_public_key)
shared_point_jacobian = other_public_key_jacobian * private_key
shared_point_affine = shared_point_jacobian.to_affine()
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8 changes: 8 additions & 0 deletions tests/crypto/crypto_test.py
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Expand Up @@ -83,6 +83,14 @@ def test_ecc(crypto_backend):
assert shared_key == bytes.fromhex(dhkey)


# -----------------------------------------------------------------------------
@pytest.mark.parametrize("x, y", [(0, 0), (1, 1)])
def test_ecc_dh_point_not_on_curve(crypto_backend, x, y):
key = EccKey.generate()
with pytest.raises(ValueError):
key.dh(x.to_bytes(32, 'big'), y.to_bytes(32, 'big'))


# -----------------------------------------------------------------------------
def test_c1(crypto_backend):
k = bytes(16)
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