def decode_from_reader(
self, reader: serialization.BinaryReader) -> EllipticCurve.ECPoint:
"""
Raises:
NotImplementedError: if an unsupported point encoding is used
TypeError: if unexpected encoding is read
"""
try:
f = reader.read_byte()
except ValueError:
return self.Infinity
f = int.from_bytes(f, "little")
if f == 0:
return self.Infinity
# these are compressed
if f == 2 or f == 3:
yTilde = f & 1
data = bytearray(reader.read_bytes(32))
data.reverse()
data.append(0)
X1 = int.from_bytes(data, 'little')
return self.decompress_from_curve(X1, yTilde)
# uncompressed or hybrid
elif f == 4 or f == 6 or f == 7:
raise NotImplementedError()
raise ValueError(f"Invalid point encoding: {f}")
def deserialize(self, reader: serialization.BinaryReader, curve=ECCCurve.SECP256R1) -> None:
try:
f0 = reader.read_byte()
except ValueError:
# infinity
self.from_bytes(b'\x00', curve, True)
return
f1 = int.from_bytes(f0, 'little')
if f1 == 0:
# infinity
self.from_bytes(b'\x00', curve, True)
return
elif f1 == 2 or f1 == 3:
data = reader.read_bytes(32)
self.from_bytes(f0 + data, curve, True)
return
else:
raise ValueError(f"Unsupported point encoding: {str(f0)}")
