SIGSALY - Revision history

Jnc: Pitch information was digitized to a 36-level form

2026-10-20T15:13:35Z

Pitch information was digitized to a 36-level form

← Older revision		Revision as of 15:13, 20 October 2026
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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.		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.

	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.		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 basic pitch information (digitized to a 36-level form), 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.

	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.		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 of the records at the exact same time, and keep them synchronized during use.

	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]].		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]].

Jnc: /* Further reading */ +Cryptology and the Origins of Spread Spectrum

2026-10-20T15:07:31Z

Further reading: +Cryptology and the Origins of Spread Spectrum

← Older revision		Revision as of 15:07, 20 October 2026
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	* Donald E. Mehl, ''The Green Hornet: America's Unbreakable Code for Secret Telephony''		* Donald E. Mehl, ''The Green Hornet: America's Unbreakable Code for Secret Telephony''
	* Donald E. Mehl, ''Top Secret Communications of WWII: Unbreakable Encryption for Secret High-level Conferences'', U.S. Army Signal Corps, Kansas City, 2002		* Donald E. Mehl, ''Top Secret Communications of WWII: Unbreakable Encryption for Secret High-level Conferences'', U.S. Army Signal Corps, Kansas City, 2002
			* David Kahn, ''Cryptology and the Origins of Spread Spectrum'', IEEE Spectrum, Volume: 21, Issue: 9, September 1984; re-printed in ''How I Discovered World War II's Greatest Spy and Other Stories of Intelligence and Code'', Auerbach, CRC Press, Boca Raton, 2014 - a good overall history, with coverage of deployment and usage, as well as technical operational detail

	==External links==		==External links==

Jnc: Better cat (had to create it)

2026-09-23T07:32:36Z

Better cat (had to create it)

← Older revision		Revision as of 07:32, 23 September 2026
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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		* 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

	[[Category: ~~History~~]]		[[Category: Security]]

Jnc: A place to hold a link to an online history

2026-09-22T14:47:56Z

A place to hold a link to an online history

New page

'''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).

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.

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.

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.

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]].

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.

==Further reading==

* 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
* Donald E. Mehl, ''The Green Hornet: America's Unbreakable Code for Secret Telephony''
* Donald E. Mehl, ''Top Secret Communications of WWII: Unbreakable Encryption for Secret High-level Conferences'', U.S. Army Signal Corps, Kansas City, 2002

==External links==

* 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

[[Category: History]]