Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site petrus.UUCP
Path: utzoo!watmath!clyde!bonnie!akgua!sdcsvax!dcdwest!ittvax!decvax!bellcore!petrus!karn
From: karn@petrus.UUCP
Newsgroups: net.crypt,net.unix
Subject: Re: Xenix & crypt
Message-ID: <323@petrus.UUCP>
Date: Mon, 8-Apr-85 14:33:55 EST
Article-I.D.: petrus.323
Posted: Mon Apr  8 14:33:55 1985
Date-Received: Wed, 10-Apr-85 05:19:44 EST
References: <111@loonam.UUCP> <133@mot.UUCP> <607@rlgvax.UUCP> <321@petrus.UUCP> <2577@nsc.UUCP>
Organization: Bell Communications Research, Inc
Lines: 18
Xref: watmath net.crypt:350 net.unix:4186

It's even easier to build a crypto system out of a "one way" function
like crypt(). Just use it as a source of hard-to-guess pseudo random
numbers, and exclusive-OR them with the plaintext. Decryption involves
generating the same series and exclusive-ORing them with the ciphertext.
There is no need to "invert" the cipher function itself.  Any pseudo-
random generator that is hard to "invert" (ie, not a linear feedback
shift register) will work. This is the "stream cipher" form of DES.

If I had the money, I'd love to set up a T1 line from here to somewhere
in Europe. Then I'd do nothing but run purely random, electronically generated
NOISE over it. The NSA would find my "code" impossible to "crack" and they'd
log it all away in the vault in hopes of being able to "decode" it someday.
Only at the T1 rate of 1.544 mb/sec, this would take about 30 inches
of 6250 bpi magtape per second, or about 93 2400' reels per day, or
33,837 reels per year. Meanwhile, I'd buy up all the land near Fort Meade
and wait for the Government to start expanding their tape storage sites...

Phil