From: tcmay@netcom.com (Timothy C. May)
Date: Mon, 7 Feb 94 10:36:25 PST
To: cypherpunks@toad.com
Subject: Re: Defeating Clipper and Skipjack is Still Possible
In-Reply-To: <199402071757.JAA17170@mail.netcom.com>
Message-ID: <199402071833.KAA22964@mail.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain


Let me briefly elaborate on a point I made in my last post:

> For voice use, this may be so (but I think pre-encryption before
> Clipper is still possible....see discussion at the end). But for the
> forthcoming _data encryption_ use (Skipjack, etc.), I don't see how
> "pre-encryption" can be detected, much less blocked, banned, or
> otherwise interfered with.  After all, "data are data."

In both this data case and the Clipper voice case, I am assuming the
keys for the pre-encryption are negotiated by either prearrangement or
by some back-channel, and don't involve D-H or any other such protocol
through the Skipjack or Clipper system.

(Perhaps this situation, where a bunch of key exchange protocols must
be gone through before communication takes place, is what Hal Finney
was referring to when he said that the Clipper proposal looks like it
will make multiple encryption impossible.)

Most of my (few) encrypted communications are by this kind of
prearrangement, with PGP being the most obvious case of this, and so a
multiple encryption scheme is workable. With voice encryption, I guess
the Clipper system will not be very cooperative with D-H and similar
protocols. 

But it will still be possible:

1. Use the Clipperphone to establish who one is communicating with.
Alice and Bob thus start talking to each other.

2. Alice says: "Switch to PGP-Voice with my P-K" (and so on).

3. Bob and Alice are thus communicating with PG-Voice, with Clipper
doing a further encryption.

If the Feds get a warrant to get the Clipper keys, then all they get
is PGP-Voice-encrypted junk.

Clipper then serves the admirable purpose of _covering_ the further
use of encryption!


--Tim May


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