Hmm, followup on my own posting... Well, who cares.

First let me try to work out the facts that we get to know about the
Clipper-Chip, from what Hellman and Denning were able to tell us:

The chip itself is not confined to (digital) telephony, but performs
general encryption in a symmetric manner.  The chip supports CFB OFB
ECB (and whatever the fourth mode of operation for DES is), the algorithm
consists of 32 rounds of *whatever*, and takes 80-Bit keys. Input data
seems to be 64 Bit? Yes.
So if two people want secure communication (whatever that means when 
Clipper is involved) they have first to agree on ONE secret key. 
(Or is it one key per direction ?)
They can exchange this key via DH-schemes or however.
Somehow the two feed their so won secret key into the Clipper-chip
which is now ready to work.
The clipper chip carries an unique Serial-Number (30 Bit's), and 160 Key-Bits.
These 160 key-bits seem to have been gained by encrypting the serial-number
with 160 seed-bits. (The seed-bits seem not to be stored in the chip)
At beginning of communication (and perhaps at certain invtervals whithin??)
before sending the fist real 64-bit output of the first encryption the Clipper
chip put's out packets (I guess 3) which represent the serial number,
and the session key. This might look like
X{ E[K; chipkeyK1+K2], serial number}
where X is a transformation of these 3? Packets involving a family-key.
This family(sp?)-key is equal for ALL chips. (X might be a simple XOR ???)
After that, the (digital?) phone-call can be done as usual, every packet
being encrypted and decrypted by Clipper.

Denning describes how K1 and K2 shall be generated, using a seed of 160
Bit's.

Now, leaving alone politics, which does not concern me as much as you, not
being an American Citicien(tm) [ :-) ] , there are some weak points in this
scheme, which might be exploited by several parties.

As far as I know about the generation of K1,K2 ; S1 and S2 look like the 
obvious backdoor. They could be used to generate the chip-keys by knowing
the serial-number (and also the family-key) of the chip. I really can't
imagine why these seeds would be needed otherwise, as true random-sources
for the generation of the K1,K2 can be bought for not to much money.

Then, the escrows. Each of them will get 80 bit of a 160-Bit key. Security
could (as little as existant) be maximized by giving them 160-bits
each, which have to be xored together to give the K1,K2. Now let's simply
assume the escrows are trustworthy, and can't be fooled by criminals or
law enforchemnt agencies. (And there will be no quarrel between escrows
and l.e.a which would hinder the l.e.a in doing their duties, and so on
and so on) Once the keys are surrendered, the corresponding
chip is compromised forever. Not very clever, IMHO [ :-)) ].
How about sending in the encrypted session-keys for each phone-call that
the police (or whoever) want's to listen to? Escrows could then simply decode
this session-key and send it back to police. (And would naturally not do this
after the warrant has expired...) This would be a better technical solution,
but I guess politics will not work that way.

Apparently (as Miss Dennings stated) the only one performing actually decodes
of intercepted messages shall be the FBI. Great. So local guys can not inter-
cept (understand) your traffic anymore. Does this mean that the FBI monopolizes
the right to do legal wiretaps ? (How is law over there, I have no idea who
is allowed to tap, and who not) This certainly means that watched communi-
cations will be routed automatically from the service-providing company
to the FBI, if the communicaiton is a watched one. And this means as far
as I understand it that the family-key has to be known by each switching-
company, and those providing cellular-phone servies etcetc. So the family-key
will not be very secret, and thus serial-numbers of calls will be readable
by anybody who cares. I _like_ traffic-analysis!

What do you guess, what happens, if you use the chip in ECB mode, and the
first few packets of the chip are somehow lost or garbled? So the session
key would not be actually broadcasted over the line? Hmmm. Shouldn't be so
difficult to do *that* :^)

And now a last point, for the other side. After all I have read and heard about
Clipper (not the programming language for dBase, is it ? [:-)]) it seems
to have many advantages, which shold not be overseen!


Now an afterthought to your rights. Please note that I have no idea what I am
talking about!!!

From: grady@netcom.com (1016/2EF221)

If this text is actually in your Bill of Rights, who can overrule this ?
But: 'Freedom of speech' is not 'Secrecy of speech'

Maybe you need to extend your Amendment #4  to cover information and
communication too ?

I am not very sure in what position your government actually is *legally*
when it tries to ban cryptography (and arms) Amendment say you may have them,
but not under what conditions. Hmm, tricky situation :-(

Actually it will make not much sense to discuss that topic in sci.crypt...
Discussion of technical details and vulnerabilites of the system are highly
suggested and appreciated :-)

Friendly greetings,

	Germano Caronni


DISCLAIMER: Everything in here is derived from things I heard and read from
other persons, so everything could be wrong. All opinions and thoughts in here
are mine, and subject to change without further notification. No warranty,
neither implicit not explicit etc. etc. etc. ad nauseam.

p.s. Please don't ask me about political opinions, as I might not bother to re-
     ply. (For further information read the last line of P. Metzgers signature)