def _decode_auth(encoded_packet: bytes) -> Tuple[Union[AuthHeader, Nonce], int]:
try:
decoded_auth, _, message_start_index = rlp.codec.consume_item(
encoded_packet, TAG_SIZE
)
except DecodingError as error:
raise ValidationError(
"Packet authentication section is not proper RLP"
) from error
if is_bytes(decoded_auth):
validate_nonce(decoded_auth)
return Nonce(decoded_auth), message_start_index
elif is_list_like(decoded_auth):
validate_length(decoded_auth, 5, "auth header")
for index, element in enumerate(decoded_auth):
if not is_bytes(element):
raise ValidationError(
f"Element {index} in auth header is not bytes: {element}"
)
auth_header = AuthHeader(
auth_tag=decoded_auth[0],
id_nonce=decoded_auth[1],
auth_scheme_name=decoded_auth[2],
ephemeral_public_key=decoded_auth[3],
encrypted_auth_response=decoded_auth[4],
)
validate_auth_header(auth_header)
return auth_header, message_start_index
else:
raise Exception("unreachable: RLP can only encode bytes and lists")
def validate_auth_header(auth_header: AuthHeader) -> None:
validate_nonce(auth_header.auth_tag)
if auth_header.auth_scheme_name != AUTH_SCHEME_NAME:
raise ValidationError(
f"Auth header uses scheme {auth_header.auth_scheme_name!r}, but only "
f"{AUTH_SCHEME_NAME!r} is supported"
)
validate_length(auth_header.id_nonce, ID_NONCE_SIZE, "id nonce")
def validate_nonce(nonce: bytes) -> None:
validate_length(nonce, NONCE_SIZE, "nonce")
def validate_aes128_key(key: AES128Key) -> None:
validate_length(key, AES128_KEY_SIZE, "AES128 key")