def _generate_AES_CBC_cipher(cek, iv):
backend = default_backend()<EOL>algorithm = AES(cek)<EOL>mode = CBC(iv)<EOL>return Cipher(algorithm, mode, backend)<EOL>
Generates and returns an encryption cipher for AES CBC using the given cek and iv.

:param bytes[] cek: The content encryption key for the cipher.
:param bytes[] iv: The initialization vector for the cipher.
:return: A cipher for encrypting in AES256 CBC.
:rtype: ~cryptography.hazmat.primitives.ciphers.Cipher