In an exclusive extract from his new book The Radio Phonics Laboratory,
Justin Patrick Moore takes us through the secret history of the links
between wartime cryptography and electro-funk
By the 1940s, radio and telephone had revolutionized communications in
the industrialized world. Its strategic use in warfare, as a way to
transmit information and intelligence, was not lost on military
personnel. Yet these signals needed to be protected. Especially with
radio, it was easy to become an undetected eavesdropper wherever
signals could be received. After World War I, the first devices to
attempt secure transmission of voice were developed. These were
substitution devices that inverted frequencies in a way similar to how
alphabetic substitution codes swapped one letter for another. High
frequencies were substituted for low frequencies and vice versa. It was
easy to make a device that could do this, but the system was also easy
to break.
In 1931, Bell Telephone Laboratories developed the A-3 scrambler that
was used by Roosevelt and Churchill when they talked on the phone.
Although the United States was still not at war in 1941, they were
aiding the Allies with materiel, and secure calls had to be made. The
A-3 worked by dividing the voice frequency into five subbands. Each of
these was inverted. On top of the measure of substitution, it also used
transposition, with the voice shifted from one subband to another every
twenty seconds.
The security of the A-3 was eventually compromised by Germans based at
a radio post in South Holland who had been intercepting the British
prime minister’s telephone calls in 1941. Aware that their system was
insecure, the situation was becoming intolerable for the Allies.
Tensions had been mounting between the US and Japan, and a “warning of
war” had come in late November, but no one knew when or where. On
December 7, 1941, American cryptanalysts were hard at work breaking a
long ciphertext intercepted from Tokyo to the Japanese embassy in
Washington D.C. The team of codebreaker William Friedman, of the
Signals Intelligence Service, had broken Japanese diplomatic ciphers
before, but this naval cipher, scrambled in fourteen parts, was
impenetrable.
One part they did tease out: the Japanese embassy had been instructed
to destroy their cryptography equipment and meet with the US Secretary
of War, suggesting that armed conflict seemed imminent. Admiral Stark,
Chief of Naval Operations, needed to send Admiral Kimmel at Pearl
Harbor another message to reinforce the warning of war. Stark knew the
A-3 scrambler was no longer secure, so he chose to send his message by
radio. However, atmospheric propagation conditions over the Pacific
stalled his message in its tracks. The next option was to send a
message by undersea cable via Western Union. Unfortunately, by the time
it arrived the battleships of the Pacific Fleet had already been bombed
and the Japanese planes were flying back to their bases.
The need for secure transmissions became even more paramount as the
United States entered the war. In 1942, the Army contracted Bell Labs
to assist with the communication problem and create “indestructible
speech” that could withstand attempts at code breaking. From this
effort, the revolutionary twelve-channel SIGSALY system was born.
SIGSALY was not an acronym, just a codename for the project. To create
SIGSALY, workers sifted through over eighty patents in the general area
of voice security, settling on Homer Dudley’s vocoder to form the basis
of the system. For SIGSALY, a twelve-channel vocoder was used. Ten of
the channels measured the power of the voice signal in the audio
portion of the frequency spectrum where most talking occurs, while two
channels were devoted to “pitch” information and whether or not
unvoiced (hiss) energy was present. The vocoder enciphered the speech
as it went out over phone or radio. In order to be deciphered at each
end of the conversation, an audio crypto-key was needed. This came in
the form of vinyl records.
From the standpoint of music history, it is interesting to note, as
Dave Tompkins did in his book How to Wreck a Nice Beach: The Vocoder
from WWII to Hip-Hop, that the SIGSALY system employed two-turntables
and a microphone. The classified name for this vinyl part of the
operation was SIGGRUV, while the vinyl records were produced by the
Muzak Corporation, a company famous for the creation of elevator music.
The sounds on these records weren’t aimed at soothing weekend shoppers
or people sitting in waiting rooms, but rather contained random white
noise, like channel 3 on an old television set. The noise was created
by the output of very large mercury-rectifier tubes that were four
inches in diameter and over a foot high. These generated wide band
thermal noise that was sampled every twenty milliseconds. The samples
were then quantized into six levels of equal probability. The level
information was converted into channels of a frequency-shift keyed
audio tone signal recorded onto a vinyl master. From the master, only
three copies of a key segment were ever made. If any SIGGRUV vinyl
still exists, and for security reasons they shouldn’t, those grooves
are critically rare.
It had to be insured that no pattern could be detected, so the records
had to be random noise. Even if the equipment had somehow been
duplicated by the Axis powers, the communications would still be
uncompromised, as they still required the matching vinyl crypto key at
each terminal. This made the transportation of these records, via
armored truck, the most secure since Edison invented the phonograph.
Just as the masters were destroyed after making three keys, each vinyl
key was only ever to be played once, as operators were instructed to
burn them after playing. The official instruction read, “The used
project record should be cut-up and placed in an oven and reduced to a
plastic biscuit of ‘Vinylite.’” As another precaution against the
grooves falling into enemy hands, the turntables themselves had a
self-destruct mechanism built into them that could be activated in case
one of the terminals was compromised. Thinking of all this adds a
fascinating new dimension to the idea of a DJ battle.
Synchronizing turntables at two different terminals across the globe
was another technical hurdle Bell Labs overcame, which was no small
feat given that if a needle jumped or the system went out of sync, only
garbled speech was heard. At the agreed upon time, say 1200 GMT,
operators listened for the click of the phonograph being cued to the
first groove. The turntables were started by releasing a clutch for the
synchronous motor that kept the turntable running at a precise speed.
Fine adjustments were made using fifty hertz phase shifters (Helmholtz
coils) to account for delays in transmission time. The operators would
listen for full quieting of the audio as synchronization was
established. Oscilloscopes and shortwave receivers were also used to
keep systems locked to international time.
A complete SIGSALY system contained about forty racks of heavy
equipment comprising vacuum tubes, relays, synchronous motors,
turntables, and custom made electromechanical equipment. In the
pre-transistor era, all of this gear required a heavy load of power, so
cooling systems were also required to keep it all from getting fried
from the heat. The average weight of a set up was about fifty-five
tons.
The system passed the inspection of Alan Turing, “the father of modern
computer science,” if not his test. He had been briefly involved with
the project on the British side, just as Claude Shannon had been in
America. On July 15, 1943, the inaugural connection was established
between the Pentagon and a room in the basement below Selfridges
Department Store in London. Eventually a total of twelve SIGSALY
encipherment terminals were established, including locations in Paris,
Algiers, Manila, Guam, Australia, and one on a barge that ended up in
the Tokyo Bay. In the year 1945 alone, the system trafficked millions
of words between the Allies.
To keep all of this operational, a special division of the Army Signal
Corp was set up: the 805th Signal Service Company. Training commenced
in a school set up by Bell Labs and soldiers were sent to various
locations, requiring security clearances and a firm grasp on the
cutting edge technology they were tasked to operate and maintain. For
every eight hours of operation, the SIGSALY systems required sixteen
hours of maintenance and calibration.
In putting the system together, eight remarkable engineering “firsts”
were achieved. A review conducted by the Institute of Electronic and
Electrical Engineers in 1983 lists them as follows:
1. The first realization of enciphered telephony
2. The first quantized speech transmission
3. The first transmission of speech by Pulse Code Modulation (PCM)
4. The first use of companded PCM
5. The first examples of multilevel Frequency Shift Keying (FSK)
6. The first useful realization of speech bandwidth compression
7. The first use of FSK – FDM (Frequency Shift Keying-Frequency
Division Multiplex) as a viable transmission method over a fading
medium
8. The first use of a multilevel “eye pattern” to adjust the sampling
intervals (a new, and important, instrumentation technique)
SIGSALY left the world with a rich inheritance that spans developments
in cryptology and digital communications, a legacy that ticks away in
the background of history every time someone hits the decks with two
turntables and a microphone.
The Radio Phonics Laboratory by Justin Patrick Moore is published by
[1]Velocity Press
References
1.
https://velocitypress.uk/product/radio-phonics-laboratory-book/
