KW-37
Encyclopedia
The KW-37, code named JASON, was an encryption system developed In the 1950s by the U.S. National Security Agency
to protect fleet broadcasts of the U.S. Navy. Naval doctrine calls for warships at sea to maintain radio silence to the maximum extent possible to prevent ships from being located by potential adversaries using radio direction finding. To allow ships to receive messages and orders, the Navy broadcast a continuous stream of information, originally in Morse code
and later using radioteletype
. Messages were included in this stream as needed and could be for individual ships, battle groups or the fleet as a whole. Each ship's radio room would monitor the broadcast and decode and forward those messages directed at her to the appropriate officer.
The KW-37 was designed to automate this process. It consisted of two major components, the KWR-37 receive unit and the KWT-37 transmit unit. Each ship had a complement of KWR-37 receivers (usually at least two) that decoded the fleet broadcast and fed the output to teleprinter machines. KWT-37's were typically located at shore facilities, where high power transmitters were located.
The KWR-37 weighed 100 pounds (45 kg) and contained some 500 subminiature vacuum tube
s, whose leads were solder
ed to printed circuit board
s. Each flip-flop
in the KW-37 required three tubes, placing an upper bound on the total number of stages in any shift registers
used at 166. Squeezing so much logic in such a small and rugged package was quite a feat in the 1950s. Later integrated circuit
technology would fit more logic than this into a wristwatch.
Each KWT-37 filled an entire relay rack with five stacked modules. A precision time reference occupied the bottom, three key generators occupied the middle and an alarm panel occupied the top position. The outputs of the three key generators were combined in a voting circuit. If one of the units' output did not match the other two, an alarm was sounded and the output from the two units that did agree continued to be used.
Each KWR-37 and each key generator in the KWT-37 had a common fill device (CFD) for loading keys (or as NSA calls them cryptovariables). The CFDs were similar to that first used in the KW-26
, accepting punched cards in Remington Rand
format. The key was changed every day at 0000 hours GMT. The receivers were synchronized to the transmitter at that time. If a receiver ever got out of sync, say due to a power failure, an operator had to set the current hour and minute on dials on the front panel. The KWR-37 would then "fast forward" through its key stream sequence until synchronization was re-established.
Large numbers of fleet broadcast key cards had to be produced and distributed to every Navy ship and many shore installations on a monthly basis, so many people had access to them. While the key cards were strictly accounted for, they were easy to copy. This proved to be a fatal weakness.
KWR-37s fell into North Korean hands when the USS Pueblo
was captured in 1968. New keying material was issued to ships throughout the world to limit the ongoing damage. In 1985 it was revealed that the Walker spy ring
had been selling key lists and cards to the Soviet Union
for decades. KW-37 systems were taken out of service by the early 1990s.
The received input to the KW(R)-37 was in the form of a multiple broadcast (multicast) signal, consisting of many channels condensed into one tone pack which was deciphered at one stage by the KW(R)-37 and then the output was sent to several KG-14's which further deciphered the then split signals into each channel of the fleet broadcast. The KG-14 also received its timing signal from the KW(R)-37; if the 37 was out of sync, all the 14's were fall out of sync as well. Each KG-14 could process one channel of the tone pack; most fleet units had six KG-14's, larger units even more.
Experiences operating the KWR-37
Typically, fleet units utilizing the KWR-37 units were outfitted with two devices for operational redundancy; that is, should one unit fail, the other one would already be online and patches via a high level, 60-milliamp patch panel would quickly be changed around so that the current offline unit could be changed over to online status at a moment's notice, and the goal here was to ensure that there was no interruption of message traffic. Since the KWR-37 units were aged and worn, sometimes the circuit cards inside had to be reseated with a rubber mallet which helped ensure the cards were reseated properly. Other problems with the KWR-37's were related to the startup times. Fleet Radiomen, and those stationed in the shore transmitting stations, had to listen to an HF signal for coordinated universal time. Radiomen called this broadcast the "time tick," which gave them a sharp tone, signalling them to press the restart button so that the unit could then start up for "new day" or otherwise known as "HJ's" by the Radiomen. This took place after the new day's crypto keylist card was properly inserted into the "crib" or the card reader by securing it onto pins and then firmly closing the card access door and then locking it with a key. Once the unit(s) were restarted, the key was placed back in the safe using two-person integrity (TPI) which was stringently enforced following the Walker spy investigation. In the early nineties when the KWR-37 units were retired from the navy and replaced by the more reliable and modern KWR-46's, fleet Radiomen breathed a sigh of relief because the KWR-37 units were often unreliable and would occasionally fall out of synchronization timing, resulting in a loss of broadcast messages from the various fleet channels.
Experiences operating the KWR-37 - a personal account from a retired US Navy fleet Radioman
National Security Agency
The National Security Agency/Central Security Service is a cryptologic intelligence agency of the United States Department of Defense responsible for the collection and analysis of foreign communications and foreign signals intelligence, as well as protecting U.S...
to protect fleet broadcasts of the U.S. Navy. Naval doctrine calls for warships at sea to maintain radio silence to the maximum extent possible to prevent ships from being located by potential adversaries using radio direction finding. To allow ships to receive messages and orders, the Navy broadcast a continuous stream of information, originally in Morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
and later using radioteletype
Radioteletype
Radioteletype is a telecommunications system consisting originally of two or more electromechanical teleprinters in different locations, later superseded by personal computers running software to emulate teleprinters, connected by radio rather than a wired link.The term radioteletype is used to...
. Messages were included in this stream as needed and could be for individual ships, battle groups or the fleet as a whole. Each ship's radio room would monitor the broadcast and decode and forward those messages directed at her to the appropriate officer.
The KW-37 was designed to automate this process. It consisted of two major components, the KWR-37 receive unit and the KWT-37 transmit unit. Each ship had a complement of KWR-37 receivers (usually at least two) that decoded the fleet broadcast and fed the output to teleprinter machines. KWT-37's were typically located at shore facilities, where high power transmitters were located.
The KWR-37 weighed 100 pounds (45 kg) and contained some 500 subminiature vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s, whose leads were solder
Solder
Solder is a fusible metal alloy used to join together metal workpieces and having a melting point below that of the workpiece.Soft solder is what is most often thought of when solder or soldering are mentioned and it typically has a melting range of . It is commonly used in electronics and...
ed to printed circuit board
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
s. Each flip-flop
Flip-flop (electronics)
In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic...
in the KW-37 required three tubes, placing an upper bound on the total number of stages in any shift registers
Linear feedback shift register
A linear feedback shift register is a shift register whose input bit is a linear function of its previous state.The most commonly used linear function of single bits is XOR...
used at 166. Squeezing so much logic in such a small and rugged package was quite a feat in the 1950s. Later integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
technology would fit more logic than this into a wristwatch.
Each KWT-37 filled an entire relay rack with five stacked modules. A precision time reference occupied the bottom, three key generators occupied the middle and an alarm panel occupied the top position. The outputs of the three key generators were combined in a voting circuit. If one of the units' output did not match the other two, an alarm was sounded and the output from the two units that did agree continued to be used.
Each KWR-37 and each key generator in the KWT-37 had a common fill device (CFD) for loading keys (or as NSA calls them cryptovariables). The CFDs were similar to that first used in the KW-26
KW-26
The TSEC/KW-26, code named ROMULUS, was an encryption system used by the U.S. Government and, later, by NATO countries. It was developed in the 1950s by the National Security Agency to secure fixed teleprinter circuits that operated 24 hours a day...
, accepting punched cards in Remington Rand
Remington Rand
Remington Rand was an early American business machines manufacturer, best known originally as a typewriter manufacturer and in a later incarnation as the manufacturer of the UNIVAC line of mainframe computers but with antecedents in Remington Arms in the early nineteenth century. For a time, the...
format. The key was changed every day at 0000 hours GMT. The receivers were synchronized to the transmitter at that time. If a receiver ever got out of sync, say due to a power failure, an operator had to set the current hour and minute on dials on the front panel. The KWR-37 would then "fast forward" through its key stream sequence until synchronization was re-established.
Large numbers of fleet broadcast key cards had to be produced and distributed to every Navy ship and many shore installations on a monthly basis, so many people had access to them. While the key cards were strictly accounted for, they were easy to copy. This proved to be a fatal weakness.
KWR-37s fell into North Korean hands when the USS Pueblo
USS Pueblo (AGER-2)
USS Pueblo is an American ELINT and SIGINT Banner-class technical research ship which was boarded and captured by North Korean forces on January 23, 1968, in what is known as the Pueblo incident or alternatively as the Pueblo crisis or the Pueblo affair. Occurring less than a week after President...
was captured in 1968. New keying material was issued to ships throughout the world to limit the ongoing damage. In 1985 it was revealed that the Walker spy ring
John Anthony Walker
John Anthony Walker, Jr. is a former United States Navy Chief Warrant Officer and communications specialist convicted of spying for the Soviet Union from 1968 to 1985, at the height of the Cold War...
had been selling key lists and cards to the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
for decades. KW-37 systems were taken out of service by the early 1990s.
The received input to the KW(R)-37 was in the form of a multiple broadcast (multicast) signal, consisting of many channels condensed into one tone pack which was deciphered at one stage by the KW(R)-37 and then the output was sent to several KG-14's which further deciphered the then split signals into each channel of the fleet broadcast. The KG-14 also received its timing signal from the KW(R)-37; if the 37 was out of sync, all the 14's were fall out of sync as well. Each KG-14 could process one channel of the tone pack; most fleet units had six KG-14's, larger units even more.
Experiences operating the KWR-37
Typically, fleet units utilizing the KWR-37 units were outfitted with two devices for operational redundancy; that is, should one unit fail, the other one would already be online and patches via a high level, 60-milliamp patch panel would quickly be changed around so that the current offline unit could be changed over to online status at a moment's notice, and the goal here was to ensure that there was no interruption of message traffic. Since the KWR-37 units were aged and worn, sometimes the circuit cards inside had to be reseated with a rubber mallet which helped ensure the cards were reseated properly. Other problems with the KWR-37's were related to the startup times. Fleet Radiomen, and those stationed in the shore transmitting stations, had to listen to an HF signal for coordinated universal time. Radiomen called this broadcast the "time tick," which gave them a sharp tone, signalling them to press the restart button so that the unit could then start up for "new day" or otherwise known as "HJ's" by the Radiomen. This took place after the new day's crypto keylist card was properly inserted into the "crib" or the card reader by securing it onto pins and then firmly closing the card access door and then locking it with a key. Once the unit(s) were restarted, the key was placed back in the safe using two-person integrity (TPI) which was stringently enforced following the Walker spy investigation. In the early nineties when the KWR-37 units were retired from the navy and replaced by the more reliable and modern KWR-46's, fleet Radiomen breathed a sigh of relief because the KWR-37 units were often unreliable and would occasionally fall out of synchronization timing, resulting in a loss of broadcast messages from the various fleet channels.
Sources
- The KWR-37 On-line Crypto Receiver — Jerry Proc: "Crypto Machines", HMCS Haida National Historic Site (2010).
Experiences operating the KWR-37 - a personal account from a retired US Navy fleet Radioman