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RACE (KL-51)
Off-line electronic cipher machine

RACE (Rapid Automatic Cryptographic Equipment) is an off-line cipher machine, developed by Standard Telefon og Kabelfabrik A/S (STK) in Norway in the late 1970s, as one of the successors to the ageing KL-7 [1]. It uses the AROFLEX cipher as one of its cryptographic algorithms and is fully electronic. RACE was used by several NATO countries and Canada. In the US the machine is known as TSEC/KL-51 and also by its National Stock Number NSN 5810-25-120-8069. The machine was phased-out from 2006 onwards, but was still in service in some countries in 2010.
Compared to other cipher machines of the same era, RACE/KL-51 is a relatively compact unit. It comes in a ruggedized beige die-cast aluminium case with a water-tight lid that protects the controls. All connections are at the rear.

The image on the right shows a typical RACE with open lid and extended paper holder. The mains cable is usually stored behind the paper holder, together with a hex wrench and spare fuses. The controls consist of a single-line red LED dot-matrix display, a high quality QWERTY keyboard and an optical paper tape reader.
KL-51 (RACE) with open lid and expanded paper holder

RACE does not feature a connection for a key fill device. Instead, keys are loaded manually (by entering them on the keyboard) or by means of an 8-level punched tape that is read by the tape reader at the front right. The reader is also used to load messages that were prepared off-line. At the rear are connections for an external Teleprinter (TP) and a paper tape puncher (Punch).

Although teleprinter networks have gradually been phased out and better IP-based alternatives have become available, some KL-51 units were still in service in the US in 2010. In most countries the machine has been replaced by modern IP-based encryption devices, such as the KIV-7. A civil version of RACE, that used a different - less powerful - algorithm, was known as Cryptel 265 [8].

We should like to thank Frode Weierud [7] for his tireless support in uncovering details about RACE/KL-51 and its history. We are also grateful to the anonymous visitor who allowed us to take detailed pictures of a RACE during an interview at Crypto Museum in February 2012 [5].
KL-51 (RACE) with closed lid KL-51 (RACE) with open lid KL-51 (RACE) with open lid and expanded paper holder KL-51 (RACE) front part Expanded paper holder Rear view with connectors visible Close-up of the keyboard Paper tape reader

All controls are located in a single area, protected by a water-tight cover. At the right is a large power switch that is used to turn the machine on and off. Turning it off, also ZEROIZES the key compartments. At the front is a full high-quality QWERTY keyboard with the usual teleprinter keys. In addition, some coloured keys are present for selecting the current mode of operation.

At the top right is a small control panel with switches to enable an external teleprinter and a tape puncher, set the desired baudrate and select the required program (i.e. the crypto-algorithm). The paper tape reader at the bottom right can be used to load the cryptographic key, but also to load an externally prepared text. It is suitable for 8-level (key) and 5-level (text) paper tapes.
Modes of operation
When operating the unit, the current mode of operation is identified with a single letter on the display (MODE). By default, the unit starts up in Plain Text mode (P). The desired MODE can be selected with the coloured keys at the top left of the keyboard. The following modes are known:
  • P - Plain text (default after reset)
  • D - Decipher
  • E - Encipher
  • F - Function (entering orders)
  • X - Error
The blue key (left) is used for entering commands (orders) and for executing them.

If an error occurs, e.g. when entering an incorrect command, the unit enters Error-mode (X) automatically. A flashing error will be displayed together with an intermittend beep.
Colorful keys

The error can be removed from the screen by pressing EREASE (bottom left) or RESET (orange function key). When entering encryption mode (ENCR) or decryption mode (DECR) the user is required to enter a valid key, either manually or via tape. At present, the format and the length of the key are unknown to us.
Tape reader
The machine has a built-in tape reader at the front, to the right of the keyboard. This tape reader accepts punched paper tape in four different formats: 5-hole (standard teleprinter, or baudot), 6-hole (TTS), 7-hole (early ASCII) and 8-hole (full ASCII). The tape should be entered from the front.
A small coin-operated screw on top of the tape reader is used to select the required paper tape format. It is likely that only 5-hole and 8-hole formats (5 and 8-bits) are supported by RACE.

Paper tape can easily be placed in the paper tape reader by opening the lid on the left and placing the tape between the two metal guides. A pin-wheel at the rear is lined up with the sprocket hole in the tape. It transports the tape when reading data. The image on the right shows the reader with its lid open. The tape guides are visible at the front. It is set for 5-hole tape.
Paper tape reader with open lid

The punched paper tape is read optically, rather than with sensing pins as on older devices. This causes less deterioration of the paper tape and makes much less noise. At the left, inside the lid, is an array of 8 LEDs that shine through the holes in the paper tape. At the right is an array of 8 photo-sensitive diodes that read the data. A disadvantage of this method is that the light sometimes shines through the tape when using very thin paper or semi-transparent plastic tape.

The 5-hole tape format is used for reading standard baudot teleprinter messages that have been prepaired off-line, e.g. on an external teleprinter. The 8-hole format (ASCII) is used when reading cryptographic key variables. This is similar to using a KOI-18 key transfer device.
Paper tape reader Paper tape reader with open lid Tape format selector

Cryptographic algorithms
RACE was the first high-end cipher machine were the cryptographic algorithms were purely implemented in software. At the time when the machine was developed this was highly unusual and STK had a lot of trouble getting the machine approved by NATO. Similar machines, like the Philips AROFLEX had their algorithms implemented in hardware; the so-called crypto logic.

The algorithms were stored in PROMs and the machine was constructed in such a way that up to five algorithms plus a test-program could be installed, simply by adding banks of PROMs on one of the machine's circuit boards. Inspired by the name of the machine, RACE, the development team decided to name each algorithm after a famous horse race track in the UK with a 5-letter name, e.g. EPSOM and DERBY. Unfortunately, they soon ran out of suitable 5-letter names.
Each algorithm, or PROGRAM as it was called, could be selected from the 6-position PROGRAM SELECTOR at the front panel, with C being the test program (CHECK) and EPSOM being the default. The following programs are known:
  • EPSOM - NATO CEROFF (Aroflex)
  • DERBY - National CEROFF
  • ASCOT - PACE compatible mode
  • EDITA - Edit Assistent
Usually, only two or three programs are present, depending on the country and application.
Program Selector

EPSOM is the default program, which is present as PROGRAM 1 on all NATO/RACE and US/KL-51 machines. It is compatible with the NATO CEROFF standard, developed by Philips Usfa for the AROFLEX. Messages created in this mode are formatted in 5-letter groups according to NATO's ACP-127 standard, just like on AROFLEX [10]. It is approved for all levels of classification.

DERBY was the Norwegian national CEROFF standard, which is similar to but not compatible with EPSOM. Is was probably only released to the Norwegian Armed Forces and national organisations. It supports two cryptografic keys, each of which provides full message protection, with special features for exclusive messages. It was approved by NATO for all levels of classification.

ASCOT is a special program for man-to-machine and machine-to-man communication. It allows the use of One-Time Pads (OTP) or the interoperable pocket size PACE encryptor (developed by Lehmkuhl in Norway) at the other end. ASCOT was also released to foreign RACE customers.

EDITA was the so-called EDIT ASSISTENT that was developed to help the operator when preparing a punched message tape for ON-LINE transmission. EDITA was also released to foreign users.
As RACE was approved by NATO, all NATO-countries had access to the machine. Although most countries bought a few machines for evaluation, only a limited number of countries officially adopted the machine. RACE (KL-51) is known to have been used by the following countries:
  • USA
  • Canada
  • Norway
  • Germany
  • Australia
  • ?
Civil version   Cryptel 265
As the cryptographic algorithms in RACE are fully implemented in software, it was easy to create a civil version with a different algorithm. The commercial machine was known as Cryptel 265 and was introduced in 1978. It was demonstrated at numerous telecommunication fairs all over the world, such as the Telecom Exhibition in Geneva in 1983, the same exhibition where the German company ANT was showing the CEROFF-compatible Philips PICOFLEX and the civil MINIFLEX.

According to the manufacturer, each crypto logic of the Cryptel 265 offered a cycle length (cryptographic period) of more than 1068 and more than 1038 possible keys (127-bits) [9].

The exterior of the Cryptel 265 was identical to RACE, but the machine was commercially not very successful, mainly due to the very strong competition in this market by Crypto AG, the Swiss-based Hagelin company. It is currently unknown how many Cryptel 265 units were sold.
In 1974, NATO was looking for a replacement for the ageing American KL-7 cipher machine, also known as ADONIS or POLLUX, that had been in service since the early 1950s. They initiated an evaluation under the name CEROFF (Cryptographic Equipment Rapid Offline) and invited several manufacturers to take part in the bidding. RACE (Rapid Automatic Cryptographic Equipment) was STK's contribution to the bidding. Another one was AROFLEX by Philips Usfa in The Netherlands.
Development of RACE had started back in 1973 at STK in Oslo, and it would be the company's first microprocessor-based cipher machine. The first prototypes used the new MIPROC processor, developed at the Norwegian Defence Research Institute (Forsvarets Forskningsinstitutt, FFI).

The 16-bit MIPROC processor was manufactured by AS Mikroelektronikk (AME) in Horten (Norway) and later by Plessey in the UK. The image on the right was taken by Frode Weierud at the Forsvarsmuseet in Oslo (Norway) [6]. It shows an early prototype of RACE with serial number 02.
RACE prototype.  Frode Weierud [6]

By the time RACE was ready for production however, STK decided to switch to the newly released Intel 8080 and port the software to the new processor. RACE allowed up to five cryptographic algorithms to be implemented (PROGRAMs), selectable by the user at the front. The first machines were delivered in 1978, several years before it was adopted by NATO and the US.

Eventually, the CEROFF-match ended in 1982 in a remittance with the Dutch AROFLEX, after Philips made the AROFLEX-algorithm available to RACE. As a result, both machines got NATO-approval and became interoperable at some level [2]. NATO chose for a split-procurement, leaving it to the end-user to decide which machine to buy; STK's RACE or Philips' Aroflex.

Although RACE was sold to a number of NATO countries and Canada, AROFLEX eventually turned out to be the more popular one in Europe and Canada [3], whilst the US chose the more robust RACE and designated it TSEC/KL-51. In total, over 5000 RACE/KL-51 machines were sold [7].
Although the KL-51 was developed during the early 1980s, some units were still in use in the late 2000s. In 2006, the US Navy was developing plans to gradually replace the remaining KL-51 units with a more modern device that could be integrated with the latest complex data networks [4].
A possible candidate for this replacement is the KIV-7, which is extremely small and is available in several variants as a commercial off-the-shelf product (COTS). The latest model is suitable for high-speed IP-based networks (KIV-7M).

KIV-7 is backwards compatible with a number of older cipher systems, such as the KG-84, and is widely used by NATO.

 More information
The KIV-7 with CIK

Help wanted
In February 2012 we were allowed to take some high resolution pictures of the machine featured on this page. At present, no further information about the KL-51 is available however. If you have more information, such as the manuals (see below) or stories about its use, please contact us.
  1. KAO-194 Operating Instructions, Offline Cryptographic Device KL-51

  2. KAO-196A KL-51 Operation Technical Manual

  1. Wikipedia, KL-51 cipher machine
    Photograph taken at the National Cryptologic Museum (NCM) at Fort Meade (USA) by Austin Mills in 2005. Source: Wikipedia Commons.

  2. Philips Usfa, Internal Memo L/5636/AvdP/JG
    Crypto Museum #301295. 23 August 1982, page 5.

  3. Museum pages of Canada's Foreign Service Communicators
    RACE: Rapid Automatic Cryptographic Equipment

  4. US Navy, R-1 Shopping List - Item No. 196
    Exhibit R-2, RDTEN Budget Item Justification. February 2006. UNCLASSIFIED.

  5. Anonymous source, Demilitarized RACE unit
    Interview with a visitor at Crypto Museum, February 2012.
    Demilitarized RACE unit kindly provided by anonymous visitor.

  6. Frode Weierud, Image of RACE prototype
    Image taken at the Forsvarsmuseets in Oslo. Date unknown. Retrieved June 2012.

  7. Frode Weirud, Crypto Historian, Personal correspondence
    Crypto Museum, June 2012.

  8. Leif Nilsen, NISnet Kick-off
    Thales Norway AS, PowerPoint presentation. 10 October 2007. Retrieved June 2012.

  9. Jane's Military Communications, Cryptel 265 Cryptographic Equipment
    Seventh edition, 1986. p. 519.

  10. Combined Communication-Electronics Board, Tape Relay Procedures
    ACP-127(G) Standard. November 1988.

  11. Hugo Ryvik, On a Secret Mission, 50 years of Norwegian cryptology
    2005. Thales internal publication. Limited edition.

Further information

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