From: Vin McLellan <vin@shore.net>
Date: Sun, 2 Feb 1997 22:26:06 -0800 (PST)
To: Adam Shostack <adam@homeport.org>
Subject: Re: "Strong" crypto and export rule changes.
Message-ID: <199702030626.WAA14616@toad.com>
MIME-Version: 1.0
Content-Type: text/plain


	Ian popped the 40-bit RC5 (not RC4) challenge with 259 processors,
almost all standard Unix college-lab workstations, as I understand it.
(RC5 has a variable block size and a variable number of rounds; but the
unknown plaintexts for this contest were enciphered using a declared
12-round RC5 with a 32-bit word size.) The message Ian revealed was
something like: "That's why you need a longer key!!!!!"

	RSA posted rewards for anyone who can break a 56-bit DES challenge
and/or any of 12 variable-length RC5 challenge messages.  The 40-bit RC5
cipher was the least of these and was expected to fall quickly.  The
initial RSA announcement of the contest emphatically declared that even
56-bit-key crypto (DES or RC5) offers only "marginal protection" against a
committed adversary -- which is not to in any way minimize Ian's
accomplishment, or the efforts (some also successful!) of others who also
tackled the 40-bit challenge.

	SDTI/RSA celebrated Ian's achievement enthusiastically at the RSA
Security Conference in San Fran last week. Burt Kalisky, the Chief
Scientist at RSA, preempted a main session at the Conference to do an
on-stage telephone interview with Ian about his attack.  SDTI (RSA)
apparently hopes to use Ian's "timely" achievement to urge Congress to
challenge the idiotic 40-bit EAR ceiling and the key-escrow contracts
required to get a 56-bit export license.

	 (The network Ian used to link his lab workstations, NOW at
Berkeley, is definitely not standard, however.  I think there is a
description of it online; but briefly, NOW seems designed to very
efficiently handle this sort of intensive distributed processing project.
More important, perhaps, was the fact that Ian just chewed through the
possible keys with a pure brute-force attack on the key space.  His attack
was not really optimized for RC5, or designed to attack any specific
element in the RC5 crypto architecture.)

	Jim Bitzos of RSA also gave a thought-provoking thumbnail summary
of the IBM Key Recovery Alliance (making a better case for it in 30 seconds
than the long technical presentatations from IBM.)  As Bitzos explained it,
the variable key-size control allows a corporate user to communicate
through encrypted links to a variety of international recipients --
dynamically adjusting the encryption mechanism to whatever varied
restrictions are required by the French, German, US, UK, etc. , govenments.

	"It's an imperfect world," growled Bitzos -- but both users and
vendors need workable mechanisms today to allow them to adapt to whatever
contraints on strong encryption that are, or will be, required by the
various national authorities.  It's a mistake, he suggested, to think of
the IBM Key Recovery Initiative soley in terms of US controls.  Many
governments are reacting with hostility to the availability of strong
encryption -- and until the Market finds a voice and educates the political
and spook cultures, commercial entities will inevitably have to adapt their
work-a-day communications security to a wide variety of national crypto
controls and key-length restrictions.

	(What I got about the IBM presentations was the realization that
there is nothing in the key recovery mechanism, per se, that requires the
recovery key to be held by a third party.  That, to my mind, is the
essential distinction between key escrow and key recovery.  I also realized
that IBM has, for years, quietly held a crucial piece of the PKC scheme in
its patented "control vector" tech, which irrevocably binds a whole set of
context-specific rules and constraints to a decryption key.  I now realize
that the control vector technology was the foundation much of the the DoD's
Blacknet development. Important stuff -- check it out!)

	Like Big Jim said, it's an imperfect world -- and likely to become
more so, from the C'punk perspective, before it becomes better.  The rumor
mill among the 2,500 cryptographers, mostly developers, who attended the
RSA Conference was pumping overtime.  One of the saddest and most
persistent rumors was that the Clinton Administration would, within months,
introduce a Congressional bill to make unescrowed strong encryption illegal
in the US.  (Personally, I'd put bitter money on that one. <sigh>)

	David Aaron, US Crypto Ambassador and the US permanent rep to the
OECD -- in which role he has strove to convince the newly liberated nations
of Eastern Europe that built-in wiretap links are essential design
components for a modern democratic nation's communications infrastructure
-- was charming and gracious... but it was no surprise that he didn't budge
a bit from the "sovereign right to listen" policy line.

	You shouldn't have skipped the RSA bash, Adam, not even for your
DCS gig in the sunny Caribbean.  There were numerous Lion and the Lamb
drinking bouts thoughout the week (some rather amazing, in terms of both
the participants and the volume of "input".) You would have loved it.
Passions often ran high, but usually in quiet intense coversations. I (one
Lamb, white wool turning gray;-) had distinct impression that there many US
government cryptographers uncomfortable with the Administration's
NSA/FBI-inspired absolutist POV.  Not even all senior feds feel that
Constitutional Law should be (re)written by FBI case agents obsessed with
making it easier to bust some two-bit crack dealer next month.  (Doesn't
mean much in the larger scheme of things, but the pained ambivalence
vividly reminded me of Vietnam debates so many years ago.)

	My favorite quote, from a federal LEA lawyer deep in his cups: "If
the colonial cops, rather than the philosophers, had drafted the
Constitution -- would Madison and Jefferson, et al, have been willing to
even put their names to it??"

	Suerte,
		_Vin

-------- In Reply To:


>Steve Schear wrote:
>| >        What the US government will allow to be exported is not "strong
>| >encryption."  It is encryption only slightly too strong to be broken
>| >by an amateur effort.  For the right investment in custom hardware, it
>| >falls quickly.  (500,000 $US = 3.5 hour avg break).
>| >
>|
>| Considering Ian's feat you certainly seem to have had your crystal
>| ball in hand.

Adam Shostack responded:

>	I wear three around my neck.  Its a new age thing.
>
>	More seriously, that estimate is the cost of breaking DES on
>custom hardware, based on Wiener's figures.  Ian got RC4-40 in 3.5
>hours on I don't know how much hardware, not a lot of it custom,
>AFAIK.

         Vin McLellan + The Privacy Guild + <vin@shore.net>
      53 Nichols St., Chelsea, MA 02150 USA <617> 884-5548