1"""OpenSSL/M2Crypto AES implementation.""" 2 3from cryptomath import * 4from AES import * 5 6if m2cryptoLoaded: 7 8 def new(key, mode, IV): 9 return OpenSSL_AES(key, mode, IV) 10 11 class OpenSSL_AES(AES): 12 13 def __init__(self, key, mode, IV): 14 AES.__init__(self, key, mode, IV, "openssl") 15 self.key = key 16 self.IV = IV 17 18 def _createContext(self, encrypt): 19 context = m2.cipher_ctx_new() 20 if len(self.key)==16: 21 cipherType = m2.aes_128_cbc() 22 if len(self.key)==24: 23 cipherType = m2.aes_192_cbc() 24 if len(self.key)==32: 25 cipherType = m2.aes_256_cbc() 26 m2.cipher_init(context, cipherType, self.key, self.IV, encrypt) 27 return context 28 29 def encrypt(self, plaintext): 30 AES.encrypt(self, plaintext) 31 context = self._createContext(1) 32 ciphertext = m2.cipher_update(context, plaintext) 33 m2.cipher_ctx_free(context) 34 self.IV = ciphertext[-self.block_size:] 35 return ciphertext 36 37 def decrypt(self, ciphertext): 38 AES.decrypt(self, ciphertext) 39 context = self._createContext(0) 40 #I think M2Crypto has a bug - it fails to decrypt and return the last block passed in. 41 #To work around this, we append sixteen zeros to the string, below: 42 plaintext = m2.cipher_update(context, ciphertext+('\0'*16)) 43 44 #If this bug is ever fixed, then plaintext will end up having a garbage 45 #plaintext block on the end. That's okay - the below code will discard it. 46 plaintext = plaintext[:len(ciphertext)] 47 m2.cipher_ctx_free(context) 48 self.IV = ciphertext[-self.block_size:] 49 return plaintext 50