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From: agr@vaxine.UUCP (Arnold Reinhold)
Newsgroups: net.crypt
Subject: primes and codes
Message-ID: <173@vaxine.UUCP>
Date: Fri, 27-Jan-84 10:25:57 EST
Article-I.D.: vaxine.173
Posted: Fri Jan 27 10:25:57 1984
Date-Received: Sat, 28-Jan-84 02:08:20 EST
Organization: Automatix Inc., Billerica, MA
Lines: 21

Recent press articles posted to net.crypt suggest that progress in
factoring large numbers poses a threat to military cryptosystems,
including nuclear launch codes.  In fact the cryptosystems threatened
are some of the "trapdoor" function public key systems that have been
proposed in the open literature in the past few years.  The idea of
the prime number trapdoor function is that you can make up a large number
that is the product of two primes and publish it.  Someone who wants to
send you a message uses the number in a encryption algorithm.  The
encrypted message can be unscrambled easily by you because you know the
two factors of the number that you published.  As long as it is too hard
for the bad guys to factor the published number, the system is secure.
The improved factoring technology suggests, at the least, numbers much larger
than 100 digits must be used for a secure system.

I know of no evidence  that the US uses public key systems of this type
for secure communications.  While current methods are secret there is
plenty of reason to believe that the people responsible for communication
security are very conservative in their methods.  Indeed the fact that
they have not classified the work at Sandia suggests they are not too
concerned.  Unfortunately the published stories will no doubt never be
corrected.