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Crypto AG
Offline one-time-tape ciper machine - this page is a stub

ULES-64 was an electronic One-Time Tape (OTT) cipher machine for encryption and decription of 5-bit digital telegraphy (telex), introduced in 1966 by Crypto AG (Hagelin) in Zug (Switzerland). It is the electronic successor to the mechanical RTE-59 and is backwards compatibile with RT/CX.

The device is based on the (unbreakable) One-Time Pad (OTP) system and offers 2 compatibility modes: modulo 26, for backward compatibility with mechanical RT/CX machines, and modulo 31 for use between two ULES-64 machines [A].

The machine is not small. It measures 650 x 365 x 356 mm and weights no less than 35 kg. It has two 5-level tape readers at the top surface – one for the message and one for the key tape – and is intended for off-line use only. The device is suitable for data speeds of 50, 75 and 100 baud, selectable by swapping one of the circuit boards.

ULES-64 marks Crypto AG's transition from (electro)mechanical OTT cipher machines, such as the C-446/RT, CX-52/RT, and TC-52, to fully electronic ones, in which the tape readers are the only moving parts. As these devices are theoretically unbreakable — they are based on the One-Time Pad (OTP) system — they were only supplied to friendly nations and were omitted from Hagelin's public brochures, as per secret licencing agreement with the Central Intelligence Agency (CIA). 1

As the name suggests, development of the ULES-64 started in late 1964 and took slightly more than one year [2]. It was officially released in January 1966 [A] and the Dutch Ministry of Foreign Affairs was one of its first users. This is remarkable, as it was used alongside the Dutch-built Philips Ecolex II and Ecolex IV, with which it was not compatible. It is therefore likely that the Dutch bought the machines for backward compatibility with their existing C-446/RT machines. The machines were supplied via the Dutch Hagelin distributor: Koopman & Co. in Amsterdam.

  1. Before 1960, Hagelin had a secret gentleman's agreement with the US National Security Agency (NSA), but this was superceeded in 1960 by a written licencing agreement with the CIA, under the codename SPARTAN.


One-Time Tape cipher machines are also known as 'mixers', as they 'mix' each plaintext letter with a random character from a keytape. The ULES-64 offers two compatibility modes:

  • CR — modulo 26
    In this mode the machine is backward compatible with the mechanical RT/CX machines and the electronic Dutch Ecolex I. Only the 26 letters of the (Latin) alphabet can be encrypted, and the SPACE-character has to be replaced by one of them. In the German version, the letter 'X' was used for 'SPACE'. In this mode, the 5 channels of the paper tape are weighted.

  • MG — modulo 31
    In this mode, all 31 characters of the ITA-2 telegraphy alphabet are supported, although some of them are are passed unaltered, and some are replaced by blanks. This ensures a properly formatted output, but makes the machine incompatible with contemporary mixers like ETCRRM and Ecolex II.
Space character
When used in modulo-26 mode, one of the 26 letters of the alphabet is assigned as replacement for the space character. This character can not be used as part of the text. Based on the language (and the wishes of the customer) the least frequently used letter will be assigned for this. If it occurs in a text, it should be replaced by another letter, or by two other letters, for example:

  • W
    e.g. Spanish, Italian
  • X
    e.g. German, Dutch
  • Z
    e.g. English
  • K
    e.g. French
ULES-64 vs Ecolex
The Dutch Government was one of the first customers of the ULES-64. They used the machine for communication between the Dutch Foreign Office in The Hague and several of its embassies. This is strange, as the Dutch had developed their own one-time tape cipher machines: the electro­mechanical Colex in 1949 and its electronic (valve-based) equivalent Ecolex I in 1950, both of which were backwards compatible with the older mechanical 26-character C-446/RT machines.

Only five units of the relay-based Colex were built, before it was succeeded by the Ecolex I. Although Ecolex I was faster then Colex, it was a complex and expensive machine — it contained 70 thermionic valves (tubes) — which was largely caused by the fact that it had to be back­wards compatible with the 26-letter C-446/RT [3]. Only 25 - 50 Ecolex I units were manufactured .

The Dutch therefore decided to develop another version of the Ecolex, which could encrypt all 32 characters of the ITA-2 telegraph alphabet. This would make the machine simpler and cheaper, but would not be backwards compatible with older machines. Development of the Ecolex Mark 2 started in 1953 — first with valves, later with transistors — and resulted in 1954 in Ecolex II, of which approx. 120 units were manufactured.
Ecolex I - interior front side

The Ecolex II was not only used by the Dutch Foreign Office, but also by the Armed Forces, as a result of which a limited number was available for embassy traffic. As a result, some of the smaller embassies still had to use the old mechanical C-446/RT or compatible hand methods.

It is likely that ULES-64 machines were ordered by the Dutch to replace the valve-based Ecolex I machines, as a gap-fill solution until better equipment would become available. Development of newer machines continued in The Netherlands, but took much longer than anticipated. Finally, from 1976 onwards, all cipher machines for embassy traffic were replaced by the Aroflex. This is corroborated by former Dutch Ambassador to Argentina Ben Bot, who recalls having worked with manual Hagelin machines (C-446/RT), which were replaced in the mid 1970s by Aroflex [4].


Like most ULES-64 machines, the one shown here has undergone a few modifications:

  1. New carrying handles at the sides
    The most abovious one is the replacement of the carrying handles at the sides. As the original hinged ones were not strong enough to carry the rather heavy machine, they were replaced by strong window grips from a local hardware store.

  2. Rear panel replaced by metal grid
    Another problem with the ULES-64 was related to temperature. As the device is built with the first generation Integrated Circuits (ICs) based on the so-called Transistor-Transistor-Logic (TTL), it generates a lot of heat. For this reason, the back panel was often replaced by a metal grid, so that the internal parts had sufficient cooling.
  1. ULES 64, Vorläufige Kurzbeschreibung
    No. 1193. Preliminary brief description (German).
    Crypto AG, Oskar Sturzinger, 6 January 1966. 1

  2. ULES-64, Circuit Diagrams
    Crypto AG, 1963-1965.
    Document kindly provided by [1] and optimised by Crypto Museum.

  1. Anonymous, ULES-64 background information
    Retrieved June 2019.

  2. Crypto AG, personal correspondence
    Crypto Museum, March 2019.

  3. Maarten Oberman, Staatsgeheim, De Beveiliging van Overheidsberichten
    State Secret, Government Communications Security (Dutch).
    2022. ISBN 978-9-4644-8870-8.

  4. VPRO Radio, Cryptoleaks. 'De Inlichtingencoup van de eeuw'
    VPRO, Argos podcast (Netherlands), 15 February 2020 (at 29:05).
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Crypto Museum. Created: Friday 26 October 2018. Last changed: Monday, 06 March 2023 - 11:20 CET.
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