[2339] in cryptography@c2.net mail archive
Re: Chaffing and winnowing - efficiency improvements
daemon@ATHENA.MIT.EDU (Bill Stewart)
Tue Mar 24 11:52:39 1998
Date: Tue, 24 Mar 1998 00:12:08 -0800
To: iang@cs.berkeley.edu (Ian Goldberg), cryptography@c2.net
From: Bill Stewart <bill.stewart@pobox.com>
In-Reply-To: <6f6gs7$b8u$1@abraham.cs.berkeley.edu>
>In article <199803231813.LAA10397@nyx10.nyx.net>,
>Colin Plumb <colin@nyx.net> wrote:
>>I can make a couple of observations. One is that since the MAC
>>attached to chaff packets is arbitrary, you might as well use the
>>wheat's MAC. E.g. you'd send (0,0,4529), (0,1,4529), (1,0,2752),
>>(1,1,2752), (2,0,9136), (2,1,9136), etc.
>>
>>This, however, lends itself to the obvious compression technique of
>>omitting the actual data bits and sending just (0,4529), (1,2752),
Cool idea.
Except you can't, because this whole charade only works by
letting you send the original, unencrypted message, with authentication,
and if you get rid of the message, you can no longer pretend
that it's not crypto, so you might as well just use efficient crypto.
>>(2,9136), etc. Rivest's Charles, along with a friend (Dawn) at Bob's
>>end, could easily convert Alice And Bob's legitimate communications to
>>this form, and Dawn could generate the redundant packets to try at the
>>far end.
>>
>>This is getting *closer* to practical. Of course, anything is
>>practical if nothing better is available due to GAK.
>
At 08:32 PM 3/23/98 GMT, Ian Goldberg wrote:
>Yup. There's also a convenient knob to twist here. If you have kick-ass
>processors communicating via a slow serial link, just up the number of bits
>you MAC in each packet (actually, only the receiver needs to be kick-ass).
>The sender transmits just the serial number and the MAC of the (8, 16,
>whatever bits) and the receiver tries all (256, 65536, whatever) combinations.
You have to be careful not to leak any data there - a MAC
that covers 8 bits in a row is much different than one that
only covers one bit.
Thanks!
Bill
Bill Stewart, bill.stewart@pobox.com
PGP Fingerprint D454 E202 CBC8 40BF 3C85 B884 0ABE 4639
