Joy Latten [off-list ref] wrote:

I am in learning mode and have been looking into CTR.
Based on the fact that CTR does not require the plaintext to 
be a multiple of the blocksize nor is padding required,
should I use cipher.c routines (as xcbc does) instead
of blkcipher.c routines (as cbc does)?
(I've been referencing rfc 3686.)

CBC is the correct model to follow.  For our purposes you
will only get multiples of blocks.  The only difference
is that unlike CBC you can chop bits off the last block
of plain text and the same bits will be chopped off in
the cipher text.

With CBC chopping off bits in either changes the other one
entirely.

Cheers,
-- 
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