From: mjr@tis.com (Marcus J Ranum)
Subject: Re: How to detect use of an illegal cipher?
Organization: Trusted Information Systems, Inc.
Lines: 23
NNTP-Posting-Host: sol.tis.com

>>How can the government tell which encryption method one is using without
>>being able to decode the traffic? i.e., In order to accuse me of using an
>>unauthorized strong encryption technique they would have to take both
>>keys out of escrow, run them against my ciphertext and "draw a blank".
>
>	I was thinking about this, also. It's quite possible the
>system transmits, in clear, the serial number of the device being
>used. That way they can start a tap, get the serial number, and use
>the warrant for the first tap to get the key.
>
>	If they tap someone who's apparently using encryption, but
>don't find that prefix, then they'll assume it's an "un-authorized"
>encryption scheme.

	This doesn't handle superencrypted traffic. If the clipper
doesn't impose any unfortunate performance side-effects there's no
reason not to use it to superencrypt a stream of triple-DES encrypted
traffic. That way your traffic looks "normal" and perhaps anyone
desiring to listen in won't even bother, since they know nobody's
going to really trust crypto that has classified internals for
important stuff.

mjr.
