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A SIGSALY terminal in 1943

During World War II, a British-American team that included Claude Shannon and Alan Turing created the first digitally scrambled, wireless phone known as SIGSALY…

Declassified only in 1976, it was a joint effort of Bell Labs and Britain’s Government Code and Cipher School at Bletchley Park, north of London. It had a scientific pedigree rivaling that of the Manhattan Project, for the British-American team included not only Shannon but also Alan Turing. They were building a system known as SIGSALY. That was not an acronym, just a random string of letters to confuse the Germans, should they learn of it.

SIGSALY was the first digitally scrambled, wireless phone. Each SIGSALY terminal was a room-sized, 55-ton computer with an iso­lation booth for the user and an air-conditioning system to prevent its banks of vacuum tubes from melting down. It was a way for Al­lied leaders to talk openly, confident that the enemy could not eavesdrop. The Allies built one SIGSALY at the Pentagon for Roo­sevelt and another in the basement of Selfridges department store for Churchill. Others were established for Field Marshal Mont­gomery in North Africa and General MacArthur in Guam. SIGSALY used the only cryptographic system that is known to be uncrackable, the ‘onetime pad.’ In a onetime pad, the ‘key’ used for scrambling and decoding a message is random. Traditionally, this key consisted of a block of random letters or numbers on a pad of paper. The encoded message therefore is random and contains none of the telltale patterns by which cryptograms can be deciphered. The problem with the onetime pad is that the key must be delivered by courier to everyone using the system, a challenge in wartime.

SIGSALY encoded voice rather than a written message. Its key was a vinyl LP record of random ‘white noise.’ ‘Adding’ this noise to Roosevelt’s voice produced an indecipherable hiss. The only way to recover Roosevelt’s words was to ‘subtract’ the same key noise from an identical vinyl record. After pressing the exact number of key records needed, the master was destroyed and the LPs distrib­uted by trusted couriers to the SIGSALY terminals. It was vitally important that the SIGSALY phonographs play at precisely the same speed and in sync. Were one phonograph slightly off, the out­put was abruptly replaced by noise.

Alan Turing cracked the German ‘Enigma’ cipher, allowing the Allies to eavesdrop on the German command’s messages. The point of SIGSALY was to ensure that the Germans couldn’t do the same. Part of Shannon’s job was to prove that the system was indeed im­possible for anyone lacking a key to crack. Without that mathemat­ical assurance, the Allied commanders could not have spoken freely. SIGSALY put several other of Shannon’s ideas into practice for the first time, among them some relating to pulse code modulation. AT&T patented and commercialized many of Shannon’s ideas in the postwar years…

The first wireless “phone”: an excerpt from William Poundstone’s Fortune’s Formula, via Delancey Place.

* Edward Snowden

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As we keep a secret, we might recall that it was on this date in 1909 that Thomas M. Flaherty filed for the first U.S. patent for a “Signal for Crossings”– a traffic signal.  His signal used a large horizontal arrow pivoted on a post, which turned to indicate the right of way direction, and was activated by an electric solenoid operated by a policeman beside the road.

Flaherty’s was the first U.S. application for a traffic signal design, later issued as No. 991,964 on May 9, 1911. But though it was filed first, it was not the first patent actually issued for a traffic signal: Ernest E. Sirrine filed a different design seven months after Flaherty; but his patent was issued earlier, and thus he held the first U.S. patent for a “Street Traffic System.”

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