def decode_aes256(cipher, iv, data, encryption_key):
    """
    Decrypt AES-256 bytes.
    Allowed ciphers are: :ecb, :cbc.
    If for :ecb iv is not used and should be set to "".
    """
    if cipher == 'cbc':
        aes = AES.new(encryption_key, AES.MODE_CBC, iv)
    elif cipher == 'ecb':
        aes = AES.new(encryption_key, AES.MODE_ECB)
    else:
        raise ValueError('Unknown AES mode')
    d = aes.decrypt(data)
    # http://passingcuriosity.com/2009/aes-encryption-in-python-with-m2crypto/
    unpad = lambda s: s[0:-ord(d[-1:])]
    return unpad(d)
Decrypt AES-256 bytes.
    Allowed ciphers are: :ecb, :cbc.
    If for :ecb iv is not used and should be set to "".