From: koontzd@lrcs.loral.com (David Koontz )
Date: Thu, 25 Aug 94 20:55:53 PDT
To: cypherpunks@toad.com
Subject: You can hide from the Chip, but not from the Man.
Message-ID: <9408260355.AA06500@io.lrcs.loral.com>
MIME-Version: 1.0
Content-Type: text/plain



After reviewing the NIST rebuttal to Matt Blaze's Paper, 'Protocol Failure
in the Escrowed Encryption Standard', referring to how the Unit ID (UID)
was expanded from 24 bits to 32 bits, I e-mailed the following question to
Dorthy Denning, informing her that I wanted to share the answer.

The question arises, does the unit ID indeed contain a field registered to
the equipment manufacturer?

Professor Denning replied:

"Yes, the UID contains bits that identify the manufacturer."

(I didn't think to ask how many)

The implication is that a counterfeit LEAF is detectible.  As per FIPS Pub
185, The Escrowed Encryption Standard, a transmission or stream of data is 
preceded by the Cryptographic Protocol Field (CPF) which is registered to a 
particular application (Clipper phone - AT&T, for example).  The CPF is used
to determine where to find the LEAF, the LEAF Creation Method (LCM) and the
Family Key (KF).  Thus the CPF also identifies the manufacturer, or group of 
manufacturers for a theoretically second sourced product, by identifying the
data protocols of the encrypted data (RCELP in the case of AT&T). 

A Bogus LEAF tested against the Escrow Authenticator (EA)  must still match
the manufacturer information found in the Unit ID.  I would expect that
there is between 10 and 12 bits of the UID specifying manufacturer.

The bad news is that to escape detection by the Law Enforcement/National
Security monitoring activity, you need to produce a LEAF that not only
produces an acceptable Escrow Authenticator used by the recipient EES
chip, but also produces a UID falling with some number of bits that matches
LE expectations as a result of examing the CPF.

The problem is that without knowledge of the Family Key and the LEAF
creation method, there is no possiblity of checking for a match in the
UID's manufacturers identifier.