Friday, April 03, 2009

Crypto Machines with One-time Keys

In my previous post I already mentioned the ETCRRM, a device to encrypt teletype signals with one-time tapes. Systems that use the principle of one-time key encryption were very popular until the 1980's, because of their absolute security. Most of these machines encrypted five-bit teletype signals by mixing (Exclusive Or function - XOR ) the plain signal with a one-time key tape. Each one-time tape consisted of truly random five-bit values and there were only two copies of each tape, one for both ends of the teletype link. Each tape was to be used only once, and destroyed after used.

Of course, the one-time tape method required a complex logistical support to securely distribute a large amount of one-time tapes. Something that could only be supported by government departments such as the military, intelligence services and diplomacy. As you can imagine, an enormous amount of one-time tapes travelled around the world by courier or in diplomatic bags, since you needed as much one-time tapes as there were message to be send.


A five bit teletype punched paper tape. Can you read it?

Although a pretty old system (developed by Gilbert Vernam in 1917) its unbreakable encryption kept it popular until sophisticated electronic crypto machines and modern computer algorithms provided enough security. Nevertheless, some electronic or software one-time key systems still exist for special purposes where absolute security has priority.

Some of the one-time key ciphering machines are the American TELEKRYPTON, B-2 PYTHON, SIGTOT and SIGSALY (which used one-time noise), the British BID-590 NOREEN (see image) and 5-UCO, the Canadian ROCKEX, the Dutch ECOLEX series, the Swiss Hagelin CD-57, CX-52 and T-55 with superencipherment, the German Siemens T-37-ICA and M-190, the East-German and T-304 LEGUAN, the Czech SD1, the Russian M-100 SMARAGD and M-105 N AGAT, and the Polish T-352/T-353 DUDEK, and of course, the Norwegian ETCRRM, famous from the Washington/Moscow hotline. I'm sure I forgot many more, any suggestions are welcome.

Apart from being unbreakable, one-time tape systems were quite simple and did not have any secret crypto technology aboard, as mixing one-time keys with plain text is a commonly known basic method of encryption. Whereas other encryption machines were considered as listed secret crypto equipment, one-time tape devices were mostly unclassified. Only the one-time tapes themselves were considered secret material. More about one-time pad on my website.

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