[PYTHON-CRYPTO] cipher feedback mode

Paul Rubin phr-pycrypt at nightsong.com
Wed Jan 29 07:23:45 CET 2003

I see the Java cipher api accepts feedback sizes down to 1 byte (8
bits) in CFB mode, but nothing smaller than that.  However, the NIST
test vectors for AES have some for 1-bit CFB mode.

Does anyone care about 1-bit CFB mode?  How about 2 bits or 4 bits?

Is there any valid use for CFB mode where the feedback size doesn't
divide the block size, like 5 bits or 23 bits?

What should be done about padding the final plaintext, when the
feedback size is smaller than the block size?  Is it ok to just
require that the total plaintext consist of an integer number of
feedback units in those cases?  What about the full-block case?

I'm trying to think of what software applications use CFB mode at all.
Anyone know of any?



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