Re: Rivest's Chaffing and Winnowing

Ge' Weijers (ge@Progressive-Systems.Com)
Mon, 23 Mar 1998 11:51:21 -0500 (EST)

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TM,

> Instead of using HMAC-SHA or another large-digest MAC, I simply used 32-bit
> CRCs to save space and time. The MAC of byte M is CRC(M+Password+M), where
> "+" denotes concatenation.

It should be fairly trivial to crack this system. CRC is so nice and
linear....... One byte at a time is not a good idea either, unless you
send O(256) packets with the same serial number. You could use 96 or 64
bits taken from the HMAC-SHA. I'm sure that this would give much better
results.

Ge'

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