def decrypt_header(self, data: bytes) -> bytes:
if len(data) != HEADER_LEN + MAC_LEN:
raise ValueError("Unexpected header length: {}".format(len(data)))
header_ciphertext = data[:HEADER_LEN]
header_mac = data[HEADER_LEN:]
mac_secret = self.ingress_mac.digest()[:HEADER_LEN]
aes = self.mac_enc(mac_secret)[:HEADER_LEN]
self.ingress_mac.update(sxor(aes, header_ciphertext))
expected_header_mac = self.ingress_mac.digest()[:HEADER_LEN]
if not bytes_eq(expected_header_mac, header_mac):
raise AuthenticationError('Invalid header mac')
return self.aes_dec.update(header_ciphertext)
def decrypt_body(self, data: bytes, body_size: int) -> bytes:
read_size = roundup_16(body_size)
if len(data) < read_size + MAC_LEN:
raise ValueError('Insufficient body length; Got {}, wanted {}'.format(
len(data), (read_size + MAC_LEN)))
frame_ciphertext = data[:read_size]
frame_mac = data[read_size:read_size + MAC_LEN]
self.ingress_mac.update(frame_ciphertext)
fmac_seed = self.ingress_mac.digest()[:MAC_LEN]
self.ingress_mac.update(sxor(self.mac_enc(fmac_seed), fmac_seed))
expected_frame_mac = self.ingress_mac.digest()[:MAC_LEN]
if not bytes_eq(expected_frame_mac, frame_mac):
raise AuthenticationError('Invalid frame mac')
return self.aes_dec.update(frame_ciphertext)[:body_size]
