class ctr : ?iv:string -> ?inc:int -> block_cipher -> block_cipher
Add Counter mode to the given block cipher. Viewing the IV
as a blocksize-byte integer in big-endian representation,
the blocks IV, IV+1, IV+2, ... are encrypted using
the given block cipher, and the result is xor-ed with the
input blocks to produce the output blocks. The additions
IV+n are performed modulo 2 to the 8 * inc power.
In other words, only the low inc bytes of the IV are
subject to incrementation; the high blocksize - inc bytes
are unaffected. inc defaults to blocksize.
The returned block cipher has the same block size as
the underlying block cipher, and is usable both for
encryption and decryption.