This method encrypts the content.
    
    :rtype: bytes

def encrypt_aes_cbc(cleartext, key, iv):
    """
    This method encrypts the content.
    
    :rtype: bytes
    """
    if isinstance(cleartext, unicode):
        cleartext = cleartext.encode('utf8')
    elif isinstance(cleartext, bytearray):
        cleartext = bytes(cleartext)
    if not isinstance(cleartext, bytes):
        raise TypeError("content to encrypt must by bytes.")
    
    aes = AES.new(key, AES.MODE_CBC, iv)
    padding = AES.block_size - (len(cleartext) % AES.block_size)
    cleartext += chr(padding).encode('utf-8') * padding # the encode() is for py3k compat
    return aes.encrypt(cleartext)