Create a new Crypt::Rijndael cipher object with the given key (which must be 128, 192 or 256 bits long). The additional $mode argument is the encryption mode, either MODE_ECB (electronic codebook mode, the default), MODE_CBC (cipher block chaining, the same that Crypt::CBC does), MODE_CFB (128-bit cipher feedback), MODE_OFB (128-bit output feedback), or MODE_CTR (counter mode).