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Create a new Crypt::Rijndael cipher object with the given key (which m
+ust be 128, 192 or 256 bits long). The additional $mode argument is t
+he encryption mode, either MODE_ECB (electronic codebook mode, the de
+fault), MODE_CBC (cipher block chaining, the same that Crypt::CBC doe
+s), MODE_CFB (128-bit cipher feedback), MODE_OFB (128-bit output feed
+back), or MODE_CTR (counter mode).