From: pgut1@cs.aukuni.ac.nz (Peter Gutmann)
Newsgroups: sci.crypt
Subject: Re: IDEA cipher (was: PGP 2.0 Announcement)
Date: 15 Sep 92 06:24:52 GMT
Organization: Computer Science Dept. University of Auckland

In <1407@eouk23.eoe.co.uk> a subliminally implanted suggestion made
    ahaley@eoe.co.uk (Andrew Haley) write:

>Peter Gutmann (pgut1@cs.aukuni.ac.nz) wrote:

>: However the patent owners, Ascom-Tech AG, are being very reasonable about
>: the patent (totally unlike PKP).  They let us use it in PGP without having
>: to pay any license fees since PGP is free, and are very approachable about
>: it's use in other programs.  Still, I ended up not using it in my PGP-compatible
>: archiver since I have a religious thing about patents - however, IDEA is a very
>: good cipher and the way the patent is being administered is one of the more
>: enlightened I've seen.

>I utterly disagree.  There is no way to describe the enforcement of an
>algorithm patent as "enlightened".  It's like saying "Frank is a good
>jailer, he doesn't tie my shackles too tight".  They (the IDEA
>licensors) _do not_ allow the free use in PGP in general, only in
>noncommercial cases.  Which means that you and I can communicate with
>PGP until we wish to discuss business; then we have to start paying
>money.

(I know followups were redirected to comp.patents but what I'm about to say
 is probably more relevant to sci.crypt)

The reason PGP uses a patented cipher is that there is no real alternative.
Triple DES is way too slow, as well as being *the* major target for US export
restrictions.  Other algorithms are either patented, have been compromised
(mainly by differential cryptanalysis), or both.  IDEA has been shown to be
more resistant to differential cryptanalysis than most other ciphers (including
DES).  It is currently under intense scrutiny by crypto experts in a number of
coutries (I think the PGP docs include information on this).

The main point here is that if there's nothing else available then using a
(as far as anyone can tell rather good) patented cipher is better than using
a do-it-yourself one of dubious security.  It's rather sad that there's
nothing good/unrestricted available for public use (they're either
export-restricted or patented or haven't been widely analyzed).  Using IDEA
was probably the best choice...

Peter.

ObFootnote: I'm religiously against software patents, and I'm not defending
  them here.  I agitated against the use of a patented cipher in PGP on the
  grounds that noone could write any PGP-compatible software without running
  into the IDEA patent, since you *must* use IDEA to read the keyrings.  One
  of the reasons the keyrings have provision for OEM cipher ID's for keyrings
  is to allow the use of non-patented algorithms to protect secret keys.  In
  my PGP-compatible archiver I use an OEM ID for the encryption algorithm
  used to protect the keys - no way I'm going to get caught up in a patent
  wrangle.  If anyone wants to protect PGP keyrings with their own non-
  patented ciphers, ID's of 64 and up are available (although it would be a
  good idea to check if anyone else is using them before you blindly define
  your own ID).

  Any comments on this scheme?
--
    pgut1@cs.aukuni.ac.nz || peterg@kcbbs.gen.nz || peter@nacjack.gen.nz
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