Re: chaffing and winnowing - some questions

Bill Stewart (bill.stewart@pobox.com)
Fri, 27 Mar 1998 10:50:52 -0800

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At 10:35 AM 3/27/98 -0500, Mordechai Ovits wrote:
>Actually, the sequence numbers do something a lot more important than
>just tell you if you missed a packet. The sequence number assures you
>that the MAC for all the zeros will be different! If you didn't include
>the sequence number with the bit, all the zeros would hash to the same
>value! Naturally, the same thing applies to the ones.

Depends on how you do the MAC; one option is to MAC the data bit and
sequence number; another is to MAC all the data bits since the beginning
of the session, in which case each MAC contains different input.
On the other hand, the latter risks differential analysis if it's
not done carefully.

>Besides for that, I suggested that the sequence numbers be removed
>*only* if you have a _reliable_ connection like TCP, as opposed to UDP.

Yep.
                                Thanks!
                                        Bill
Bill Stewart, bill.stewart@pobox.com
PGP Fingerprint D454 E202 CBC8 40BF 3C85 B884 0ABE 4639

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