https://gunkies.org/index.php?action=history&feed=atom&title=SIGSALYSIGSALY - Revision history2026-09-22T16:55:44ZRevision history for this page on the wikiMediaWiki 1.43.9https://gunkies.org/w/index.php?title=SIGSALY&diff=37253&oldid=prevJnc: A place to hold a link to an online history2026-09-22T14:47:56Z<p>A place to hold a link to an online history</p>
<p><b>New page</b></p><div>'''SIGSALY''' (not an acronym; also known as '''X System''' and '''Green Hornet'''; the latter from the noise it made, in operation) was a technologically very advanced (for its day) [[digital]] [[encryption|encrypted]] [[radio]] speech system, created by [[Bell Laboratories]] during World War II. It first went into service in 1943, and was used extensively during the war for direct, live communication among top Allied leaders (e.g. Churchill and Roosevelt).<br />
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It first converted speech into a [[bit]] stream with a [[vocoder]]; that bit stream was then encrypted with the equivalent of a 'one-time pad'; the resulting encrypted bit steam was then transmitted to the other end of the link over an [[Frequency Modulation|FM]] radio link.<br />
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The first step was done by dividing the incoming speech signal (with [[frequency|frequencies]] in the 250-3000 Hz range) into 10 frequency bands, and measuring and digitizing the [[amplitude]] of the signal in each band, with six amplitude levels (i.e. values of 0-5) for each. In addition to those 10 channels, two additional channels were used; one for pitch information, and one for whether the speech was voiced or un-voiced (i.e. a sibilant, or 'hiss'). All channels were sampled 50 times per second.<br />
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The bit steam which was the key, used in the encryption/decryption stage, was [[quantum]] thermal [[noise]] recorded onto a phonograph record; only two copies of each one were produced, one for each end. Complex electro-mechanical mechanisms were required to start the playback at the exact same time, and keep them synchronized during use.<br />
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A galaxy of talent was brought in to help create it; [[Claude Shannon]] and [[Harry Nyquist]] made important contributions, and [[Alan Turing]] advised on the cryptography stage. A SIGSALY terminal was constructed of [[vacuum tube]] technology (the only thing available at the time), and as a result was physically massive: 40 racks of equipment weighing over 50 tons. In operation, it used about 30 kW of [[electricity]].<br />
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The Germans had easily broken the previous 'scrambler' technique used in an attempt to secure voice communications. Although they recorded a lot of SIGSALY traffic, they never made any inroads into it (in fact, they had wrongly decided that it encoded a telegraphic system of some sort). Indeed, using as it does a completely random one-time key, it would probably be unbreakable even today.<br />
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==Further reading==<br />
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* M. D. Fagen (editor), ''National Service in War and Peace (1925–1975)'', Volume II of ''A History of Engineering and Science in the Bell System'', Bell Telephone Laboratories, Murray Hill, 1978 - pp. 296–317<br />
* Donald E. Mehl, ''The Green Hornet: America's Unbreakable Code for Secret Telephony''<br />
* Donald E. Mehl, ''Top Secret Communications of WWII: Unbreakable Encryption for Secret High-level Conferences'', U.S. Army Signal Corps, Kansas City, 2002<br />
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==External links==<br />
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* J. V. Boone and R. R. Peterson, [https://www.nsa.gov/portals/75/documents/about/cryptologic-heritage/historical-figures-publications/publications/wwii/sigsaly.pdf ''The Start of the Digital Revolution: SIGSALY - Secure Digital Voice Communications in World War II''], Center for Cryptologic History, National Security Agency, Fort George G. Meade, July 2000 <br />
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[[Category: History]]</div>Jnc