def create_symmetric_decryption_ctx(self, cipher, mode): if (isinstance(mode, CTR) and isinstance(cipher, AES) and not self._evp_cipher_supported(cipher, mode)): # This is needed to provide support for AES CTR mode in OpenSSL # 0.9.8. It can be removed when we drop 0.9.8 support (RHEL 5 # extended life ends 2020). return _AESCTRCipherContext(self, cipher, mode) else: return _CipherContext(self, cipher, mode, _CipherContext._DECRYPT)