The TSEC/KL-7, also known as Adonis was an off-line non-reciprocal rotor encryption machine.A History of U.S. Communications Security; the David G. Boak Lectures
National Security Agency (NSA), Volume I, 1973, partially released 2008, additional portions declassified October 14, 2015 The KL-7 had rotors to encrypt the text, most of which moved in a complex pattern, controlled by notched rings. The non-moving rotor was fourth from the left of the stack. The KL-7 also encrypted the message indicator.

History and development

In 1952, the machine was introduced by AFSA's successor, the

U.S. The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

National Security Agency The National Security Agency (NSA) is a national-level intelligence agency of the United States Department of Defense, under the authority of the Director of National Intelligence (DNI). The NSA is responsible for global monitoring, collect ...

, in the US Army, Navy and Air Force. In the early 1960s, the AFSAM-7 was renamed TSEC/KL-7, following the new standard crypto nomenclature. It was the most widely used crypto machine in the US armed forces until the mid-1960s and was the first machine capable of supporting large networks that was considered secure against

known plaintext attack The known-plaintext attack (KPA) is an attack model for cryptanalysis where the attacker has access to both the plaintext (called a crib), and its encrypted version (ciphertext). These can be used to reveal further secret information such as secre ...

. Some 25,000 machines were in use in the mid-1960s. The KL-7 was also used by several

NATO The North Atlantic Treaty Organization (NATO, ; french: Organisation du traité de l'Atlantique nord, ), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states – 28 European and two No ...

countries until 1983. An 8-rotor version sent indicators in the clear and was code named POLLUX. The encrypted or decrypted output of the machine was printed on a small paper ribbon. It was the first cipher machine to use the re-entry (re-flexing) principle, discovered by Albert W. Small, which re-introduces the encryption output back into the encryption process to re-encipher it again. The research for the new cipher machine, designated MX-507, was initiated in 1945 by the Army Security Agency (ASA) as a successor for the

SIGABA In the history of cryptography, the ECM Mark II was a cipher machine used by the United States for message encryption from World War II until the 1950s. The machine was also known as the SIGABA or Converter M-134 by the Army, or CSP-888/889 by th ...

and the less secure Hagelin

M-209 In cryptography, the M-209, designated CSP-1500 by the United States Navy (C-38 by the manufacturer) is a portable, mechanical cipher machine used by the US military primarily in World War II, though it remained in active use through the Korean W ...

. Its development was turned over to the newly formed Armed Forces Security Agency (AFSA) in 1949. The machine was renamed AFSAM-7, which stands for Armed Forces Security Agency Machine No 7. It was the first crypto machine, developed under one centralized cryptologic organisation as a standard machine for all parts of the armed forces, and it was the first cipher machine to use electronics (vacuum tubes), apart from the British

ROCKEX Rockex, or Telekrypton, was an offline one-time tape Vernam cipher machine known to have been used by Britain and Canada from 1943. It was developed by Canadian electrical engineer Benjamin deForest Bayly, working during the war for British Secur ...

, which was developed during World War 2.

Description

The KL-7 was designed for off-line operation. It was about the size of a

Teletype A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point and point-to-multipoint configurations. Init ...

machine and had a similar three-row keyboard, with shift keys for letters and figures. The KL-7 produced printed output on narrow paper strips that were then glued to message pads. When encrypting, it automatically inserted a space between five-letter code groups. One of the reasons for the five letter groups was messages might be given to a morse code operator. The number of five letter groups was easily verified when transmitted. There was an adaptor available, the HL-1/X22, that allowed 5-level Baudot punched paper tape from

equipment to be read for decryption. The standard KL-7 had no ability to punch tapes. A variant of the KL-7, the KL-47, could also punch paper tape for direct input to teleprinters.

Product details

Each rotor had 36 contacts. To establish a new encryption setting, operators would select a rotor and place it in a plastic outer ring at a certain offset. The ring and the offset to use for each position were specified in a printed key list. This process would be repeated eight times until all rotor positions were filled. Key settings were usually changed every day at midnight,

GMT Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, including being calculated from noon; as a cons ...

. The basket containing the rotors was removable, and it was common to have a second basket and set of rotors, allowing the rotors to be set up prior to key change. The old basket could then be kept intact for most of the day to decode messages sent the previous day, but received after midnight. Rotor wiring was changed every 1 to 3 years. The keyboard itself was a large sliding switch, also called permutor board. A signal, coming from a letter key, went through the rotors, back to the permutor board to continue to the printer. The KL-7 was non-reciprocal. Therefore, depending on the ''Encipher'' or ''Decipher'' position of the permutor board, the direction of the signal through the rotors was changed. The rotor basket had two sets of connectors, two with 26 pins and two with 10 pins, at each end that mated with the main assembly. Both 26 pin connectors were connected to the keyboard to enable the switching of the signal direction through the rotors. Both 10 pin connectors on each side were hard-wired with each other. If a signal that entered on one of the 26 pins left the rotor pack on one of these 10 pins, that signal was redirected back into the rotors on the entry side to perform a new pass through the rotors. This loop-back, the so-called re-entry, created complex scrambling of the signal and could result in multiple passes through the rotor pack, depending on the current state of the rotor wiring. There was also a switch pile-up under each movable rotor that was operated by

cam Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bin ...

s on its plastic outer ring. Different outer rings had different arrangements of cams. The circuitry of the switches controlled solenoids which in turn enabled the movement of the rotors. The combination of cam rings and the controlling of a rotor by several switches created a most complex and irregular stepping. The exact wiring between switches and solenoids is still classified. KL-7

The KL-7 was largely replaced by electronic systems such as the

KW-26 The TSEC/KW-26, code named ROMULUS, (in 1966 the machine based encryption system was not code-named "Romulus," rather the code-name was "Orion," at least in the US Army's variant) was an encryption system used by the U.S. Government and, later, ...

ROMULUS and the

KW-37 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 ext ...

JASON in the 1970s, but KL-7s were kept in service as backups and for special uses. In 1967, when the

U.S. Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage o ...

sailor

John Anthony Walker John Anthony Walker Jr. (July 28, 1937 – August 28, 2014) was a United States Navy chief warrant officer and communications specialist convicted of spying for the Soviet Union from 1967 to 1985 and sentenced to life in prison. In lat ...

walked into the embassy of the

Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...

Washington, DC ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan ...

seeking employment as a spy, he carried with him a copy of a key list for the KL-47. KL-7s were compromised at other times as well. A unit captured by

North Vietnam North Vietnam, officially the Democratic Republic of Vietnam (DRV; vi, Việt Nam Dân chủ Cộng hòa), was a socialist state supported by the Soviet Union (USSR) and the People's Republic of China (PRC) in Southeast Asia that existed f ...

is on display at NSA's

National Cryptologic Museum The National Cryptologic Museum (NCM) is an American museum of cryptologic history that is affiliated with the National Security Agency (NSA). The first public museum in the U.S. Intelligence Community, NCM is located in the former Colony Sev ...

. The KL-7 was withdrawn from service in June 1983, and

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

's last KL-7-encrypted message was sent on June 30, 1983, "after 27 years of service." The successor to the KL-7 was the KL-51, an off-line, paper tape encryption system that used digital electronics instead of rotors. Adonis 26 point rotors

Notes

Britannica (2005). Proc (2005) differs, saying that, "''after the Walker family spy ring was exposed in the mid-1980s (1985)...immediately, all KL-7's were withdrawn from service''"

References

Sources

Jerry Proc's page on the KL-7
retrieved 2012-08-28.
NSA Crypto Almanac 50th Anniversary - The development of the AFSAM-7
retrieved February 27, 2011.

from Dirk Rijmenants' Cipher Machines & Cryptology, retrieved February 27, 2011.
Patent for Rotor Re-entry by Albert W Small, filed 1944
from Free Patents On-line, retrieved February 27, 2011.
"Cryptology", Encyclopædia Britannica. Retrieved 22 June 2005 from Encyclopædia Britannica Online
* Card attached to KL-51 on display at the

, 2005.

External links

TSEC/KL-7 with detailed information and many images
on the Crypto Museum website

on Dirk Rijmenants' Cipher Machines & Cryptology
Accurate TSEC/KL-7 Simulator (Java, platform-independent)
released by MIT, on Crypto Museum website {{Cryptography navbox , machines Rotor machines National Security Agency encryption devices Computer-related introductions in 1949 Products introduced in 1949