class cbc_encrypt :Add Cipher Block Chaining (CBC) to the given block cipher in encryption mode. Each block of input is xor-ed with the previous output block before being encrypted through the given block cipher. The optional?iv:string -> block_cipher ->
block_cipher
iv
argument specifies the string to be xor-ed
with the first input block, and defaults to all zeroes.
The returned block cipher has the same block size as the
underlying block cipher.