Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version VT2.1 1/30/84; site vortex.UUCP Path: utzoo!watmath!clyde!floyd!harpo!decvax!vortex!lauren From: lauren@vortex.UUCP (Lauren Weinstein) Newsgroups: net.crypt Subject: secure codes Message-ID: <239@vortex.UUCP> Date: Mon, 30-Jan-84 06:34:35 EST Article-I.D.: vortex.239 Posted: Mon Jan 30 06:34:35 1984 Date-Received: Wed, 8-Feb-84 04:42:38 EST Organization: Vortex Technology, Los Angeles Lines: 28 In cases of very important military or diplomatic communications, I believe that the coding technique of choice is still the time-honored "one-time" code. This technique involves pre-sending to your destination (by trusted means, such as inside a diplomatic pouch) a long "sequence" of data to be used for encryption and/or decryption purposes. Essentially, the concept is simple. For each byte you wish to encode/decode, you perform some function based on that byte and the NEXT byte in the coding "sequence". You never use the same sequence data byte twice, and the coding sequence itself (magnetic tape, ROM, or whatever) is also never used again. The coding sequence itself would normally be as random as possible (for example, based on the "noise" generated by the decay of a radioactive particle). In the old days, the coding sequence was sent on paper, thusly the term "one-time pad." Today, such data would usually be sent on magnetic tape, on ROMs within calculator-like encoding/decoding devices, or by similar means. Of course, old-style pads are still a possibility in some cases. One-time codes are generally considered to be essentially impossible to crack, since there is no "key" nor pattern to uncover. They are generally reserved for important communications, since they involve considerable logistic problems, including maintaining the sync between the encoding/decoding sides of the communication using the sequence data, and the hassles of delivering the sequence data to the destination party in the first place. --Lauren--