PyORAM/src/pyoram/crypto/aes.py

   1 __all__ = ("AES",)
   2
   3 import os
   4 import cryptography.hazmat.primitives.ciphers
   5 import cryptography.hazmat.backends
   6
   7 _backend = cryptography.hazmat.backends.default_backend()
   8 _aes = cryptography.hazmat.primitives.ciphers.algorithms.AES
   9 _cipher = cryptography.hazmat.primitives.ciphers.Cipher
  10 _ctrmode = cryptography.hazmat.primitives.ciphers.modes.CTR
  11 _gcmmode = cryptography.hazmat.primitives.ciphers.modes.GCM
  12
  13 class AES(object):
  14
  15     key_sizes = [k//8 for k in sorted(_aes.key_sizes)]
  16     block_size = _aes.block_size//8
  17
  18     @staticmethod
  19     def KeyGen(size_bytes):
  20         assert size_bytes in AES.key_sizes
  21         return os.urandom(size_bytes)
  22
  23     @staticmethod
  24     def CTREnc(key, plaintext):
  25         iv = os.urandom(AES.block_size)
  26         cipher = _cipher(_aes(key), _ctrmode(iv), backend=_backend).encryptor()
  27         return iv + cipher.update(plaintext) + cipher.finalize()
  28
  29     @staticmethod
  30     def CTRDec(key, ciphertext):
  31         iv = ciphertext[:AES.block_size]
  32         cipher = _cipher(_aes(key), _ctrmode(iv), backend=_backend).decryptor()
  33         return cipher.update(ciphertext[AES.block_size:]) + \
  34                cipher.finalize()
  35
  36     @staticmethod
  37     def GCMEnc(key, plaintext):
  38         iv = os.urandom(AES.block_size)
  39         cipher = _cipher(_aes(key), _gcmmode(iv), backend=_backend).encryptor()
  40         return iv + cipher.update(plaintext) + cipher.finalize() + cipher.tag
  41
  42     @staticmethod
  43     def GCMDec(key, ciphertext):
  44         iv = ciphertext[:AES.block_size]
  45         tag = ciphertext[-AES.block_size:]
  46         cipher = _cipher(_aes(key), _gcmmode(iv, tag), backend=_backend).decryptor()
  47         return cipher.update(ciphertext[AES.block_size:-AES.block_size]) + \
  48                cipher.finalize()