def point_from_pub_key(pub_key: PubKey, ec: Curve = secp256k1) -> Point:
"Return an elliptic curve point tuple from a public key."
if isinstance(pub_key, tuple):
if ec.is_on_curve(pub_key) and pub_key[1] != 0:
return pub_key
raise BTClibValueError(f"not a valid public key: {pub_key}")
if isinstance(pub_key, BIP32KeyData):
return _point_from_xpub(pub_key, ec)
try:
return _point_from_xpub(pub_key, ec)
except (TypeError, BTClibValueError):
pass
# it must be octets
try:
return point_from_octets(pub_key, ec)
except (TypeError, ValueError) as e:
raise BTClibValueError(f"not a public key: {pub_key!r}") from e
def point_from_octets(pub_key: Octets, ec: Curve = secp256k1) -> Point:
"""Return a tuple (x_Q, y_Q) that belongs to the curve.
Return a tuple (x_Q, y_Q) that belongs to the curve according to
SEC 1 v.2, section 2.3.4.
"""
pub_key = bytes_from_octets(pub_key, (ec.p_size + 1, 2 * ec.p_size + 1))
bsize = len(pub_key) # bytes
if pub_key[0] in (0x02, 0x03): # compressed point
if bsize != ec.p_size + 1:
err_msg = "invalid size for compressed point: "
err_msg += f"{bsize} instead of {ec.p_size + 1}"
raise BTClibValueError(err_msg)
x_Q = int.from_bytes(pub_key[1:], byteorder="big")
try:
y_Q = ec.y_even(x_Q) # also check x_Q validity
return x_Q, y_Q if pub_key[0] == 0x02 else ec.p - y_Q
except BTClibValueError as e:
msg = f"invalid x-coordinate: '{hex_string(x_Q)}'"
raise BTClibValueError(msg) from e
elif pub_key[0] == 0x04: # uncompressed point
if bsize != 2 * ec.p_size + 1:
err_msg = "invalid size for uncompressed point: "
err_msg += f"{bsize} instead of {2 * ec.p_size + 1}"
raise BTClibValueError(err_msg)
x_Q = int.from_bytes(pub_key[1:ec.p_size + 1],
byteorder="big",
signed=False)
Q = x_Q, int.from_bytes(pub_key[ec.p_size + 1:],
byteorder="big",
signed=False)
if Q[1] == 0: # infinity point in affine coordinates
raise BTClibValueError(
"no bytes representation for infinity point")
if ec.is_on_curve(Q):
return Q
raise BTClibValueError(f"point not on curve: {Q}")
else:
raise BTClibValueError(f"not a point: {pub_key!r}")