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""" symenc.py
"""
from cryptography.exceptions import UnsupportedAlgorithm
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.ciphers import Cipher
from cryptography.hazmat.primitives.ciphers import modes
from .errors import PGPDecryptionError
from .errors import PGPEncryptionError
from .errors import PGPInsecureCipherError
__all__ = ['_encrypt',
'_decrypt']
def _encrypt(pt, key, alg, iv=None):
if iv is None:
iv = b'\x00' * (alg.block_size // 8)
if alg.is_insecure:
raise PGPInsecureCipherError("{:s} is not secure. Do not use it for encryption!".format(alg.name))
if not alg.is_supported:
raise PGPEncryptionError("Cipher {:s} not supported".format(alg.name))
try:
encryptor = Cipher(alg.cipher(key), modes.CFB(iv), default_backend()).encryptor()
except UnsupportedAlgorithm as ex: # pragma: no cover
raise PGPEncryptionError from ex
else:
return bytearray(encryptor.update(pt) + encryptor.finalize())
def _decrypt(ct, key, alg, iv=None):
if iv is None:
"""
Instead of using an IV, OpenPGP prefixes a string of length
equal to the block size of the cipher plus two to the data before it
is encrypted. The first block-size octets (for example, 8 octets for
a 64-bit block length) are random, and the following two octets are
copies of the last two octets of the IV.
"""
iv = b'\x00' * (alg.block_size // 8)
try:
decryptor = Cipher(alg.cipher(key), modes.CFB(iv), default_backend()).decryptor()
except UnsupportedAlgorithm as ex: # pragma: no cover
raise PGPDecryptionError from ex
else:
return bytearray(decryptor.update(ct) + decryptor.finalize())
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