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R.M.M. Oberman
Professor, scientist and inventor

Prof. Dr. Ir. Roelof Maarten Marie Oberman (Leiden, 12 Juni 1910 – Wageningen 19 March 1989) (age 78) was a Dutch academic who worked as a developer for the Dr. Neher Laboratory in Leid­schendam (Netherlands) – at the time the prestigious research department of the Dutch state-owned telecom monopolist PTT – and later as a professor at the Delft University of Technology. 1

After graduating twice from the Delft University of Technology, Oberman began working for the Dutch state-owned telecom monopolist PTT in 1935, where he became responsible for the development of the telegraphy network (telex).

In 1946 he made the move to the prestigious Dr. Neher Laboratory of the PTT in Leidschendam (Netherlands) — at the time regarded the state laboratory of The Netherlands. In his capacity as senior developer at the Lab, he developed the first Dutch post-war One-Time Tape (OTT) cipher machine (a relay-based mixer known as Colex) at the request of the Dutch Government.

Colex evolved into Ecolex I (Mark 1 and Mark 2), and Ecolex II, all of which were eventually taken over and produced in quantity for the Dutch Foreign Ministry, the Department of Defense and NATO, by Philips Usfa in Eindhoven. It marked the start of Philips as a worldwide crypto-player.
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In 1949, at the official commissioning of the Colex cipher machine between five embassies and the Dutch Foreign Office in The Hague, Oberman was decorated Officier in de Orde van Oranje-Nassau (Officer of the Order of Orange-Nassau) by Dutch Prime Minister Willem Drees.

Apart from cipher machines, Oberman also developed an allotment machine for the Dutch State Lottery (Staatsloterij), which was a spin-off from the Erolet key tape generator that he had developed for the Colex and Ecolex cipher machines. In 1947, whilst working at PTT, Oberman became a teaching assignment at the Delft University of Technology, where in 1949 he became an extaordinary professor. In 1958, he left the Dr. Neher Lab of the PTT to become full time Professor at Delft University, where he lectured switching technology – at the time the building blocks of telephone switches and cipher machines – until his retirement in 1980.

During his lifetime, Oberman filed more than 90 patents, most of which were registered in multiple countries, including Germany, the UK and the USA. Many of his inventions involved (telephone) switching systems, for which the patents were filed on behalf of the Dutch State or the PTT. Philips Usfa filed 9 patents in which Oberman and Snijders are listed as the inventors.

 Full biography

  1. At the time known as Technische Hogeschool Delft, abbreviated TH Delft.

Related subjects on this website
PTT Colex (predecessor of Ecolex)
Ecolex I, developed by PTT, manufactured by Philips Usfa
Ecolex I Mark 2, developed by PTT, never produced in quantity
Ecolex III, developed by PTT, prototypes manufactured by Philips Usfa
Dutch Post Office (PTT, later: KPN)
Staatsgeheim (State Secret) book by Maarten Oberman
Known developments
The following products were (co)developed by R.M.M. Oberman:

Book about Dutch state secrets
In 2022, Oberman's son Maarten released a book about the history of cipher machines in The Netherlands after WWII, from 1945 to 1970, in which his father played a key role. The book is based on Oberman's personal archive, along with declassified material from the Dutch General Intelligence Service AIVD and documents from the Dutch National Archives.

The hard-cover book contains 260 full-colour pages and is written in the Dutch language.

 More information

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Oberman graduated in 1932 as Mechanical Engineer (Ir.) at the Technical University of Delft (Netherlands). As there wasn't much work at the time, he was given the opportunity to stay on, as a result of which he graduated again in 1935 as Electronics Engineer (Ir.).

After his graduation, he found a job as Telegraph Engineer at the PTT district of Den Bosch (Netherlands). A year later, in 1936, he became chief of the technical service department of the PTT's Telegraph Office in Rotterdam. In August 1940 he was transferred to the PTT headquarters in The Hague, where he became responsible for the Telegraphy Department.

After the war, in 1946, Oberman became head of the equipment department at the Dr. Neher Laboratory of the PTT. In 1947, he graduated cum laude at Delft University, and became Doctor of Technical Sciences, with his dissertation The Bridge Marker Key Automatic Switching System.

In May 1947 he was given a teaching assignment at Delft University, and in 1949 became extraordinary Professor with a chair in Switching Technology. In 1958 he became a full time Professor in Switching Technology — the technology behind information processing systems, telegraphy, telephone switches and also behind cipher machines. Until that time (1958) he had worked at the PTT was well as at Delft University. In 1980 he retired at the age of 70.

Cipher machines
During and also due to WWII it had become clear that message communication systems were prone to malicious interception, also known as co-reading or eavesdropping, even if they were cryptographically protected. This happened with the Enigma cipher machine, but also to the Dutch WWII Intelligence Bureau (BI), which suffered great losses because its messages had been read by the enemy. Immediately after the war, in 1946, the Dutch Government therefore asked the PTT whether it was possible to develop a secure telegraph system, that would be immune to cryptanalytic attacks. They did not want to buy such systems from foreign manufacturers, as they were afraid that they might have hidden weaknesses or, worse, a deliberately built-in backdoor.

The question finally landed on Oberman's desk in 1946/47, as he was responsible for telegraphy matters within the PTT. This led to the development of the Colex machine — Codetelex — which, after two trial versions, met the requirement of all parties involved. Colex was a One-Time Tape cipher machine – a practical implementation of the unbreakable One-Time Pad (OTP) for use in telegraphy communications – and consisted of two parts: a mixer and a key generator. When the latter meets the requirements of true randomness, the system can be proven mathematically to be (forever) unbreakable. The first implementation was completely relay-based, due to the post-war lack of electronic components, and was capable of encrypting just 3 characters per second.

The disadvantage of One-Time Tape is the problem of key distribution. Based on the Vernam Cipher, the key has to be at least as long as the message, and can only be used once, to prevent successful cryptanalytic attacks. Furthermore, it cannot be used by multiple parties and must be destroyed after use. A stringent procedure is required for generating and distributing the key tapes, but it was (and still is) the only way to technically ensure that State Secrets are kept secret.

Part of original circuit diagram of the Colex cipher machine. Copyright Crypto Museum.

The mixing part of the Colex (i.e. the mixer) was constructed with approx. 100 electromechanical relays that mix each letter of the plaintext with a character from the key tape, using an operation that was carried out with a mix and unmix feature. Several years later this became known as the exlusive-OR operation (XOR), also known as modulo-2 addition. If both parties have the same key tape and use it from the same starting position onwards (i.e. synchronised), the recipient has to perform the same XOR operation in order to reveal the plaintext again.

One of the critical parts of the system is the key generator, which Oberman had named Roulette. Facing the lack of electronic parts immediately after the war, he composed a creative solution to obtain and control randomness of the key production in the Colex system. It comprises a 400 kHz oscillator of which the output is divided by 2 in five stages. Each stage produces one of the five bits of the ITA2 telegraph alphabet (Baudot), whilst a relay is used to sample the output at ~225 ms intervals. The uncertainty of the movement of the electromechanical relay is used as the source of randomness (noise). To check whether the noise was evenly distributed, a set of five electromechanical counters were connected to the machine, allowing the user to check whether each of the five output bits appeared on the key tape an (approximate) equal number of times.

Oberman's signature on the original Colex circuit diagram

The Colex was built by a small team under Oberman, and was put into service in on 5 April 1949 by Dutch Prime Minister Willem Drees. It was used for communication between the Foreign Office and the embassies in London (UK), Paris (France), Washington (USA) and Jakarta (Indonesia).

 More about Colex

Colex was succeeded by EcolexElectronic Codetelex — in which the electromechanical relays were replaced by thermionic valves (vacuum tubes). This system was later renamed Ecolex I, and was succeeded around 1955 by Ecolex II, in which the valves were replaced by transistors. In the same vein, the Roulette key generator was succeeded by Erolet, short for Electronic Roulette.

During the development of Colex and Ecolex, Oberman was a member of several commissions, including Crypto Apparatuur Commissie (CAC) – the crypto equipment commission – and Code Coördinatie Bureau, the Dutch Cipher Authority.

As Oberman's employer — PTT — was a service provider and not an equipment manufacturer, the production of cipher machines was not regarded as core business, as a result of which in 1956 the production of the Ecolex machines was transferred to Philips Usfa in Eindhoven (Netherlands), who also took over development.

In 1958, Oberman left the PTT to become full time Professor at Delft University. His major subject was switching technology (logic), of which cryptography increasingly became part, especially when in the 1960s cipher machines became based on electronic shift registers.
Ecolex I - interior front side

In 1963 Philips released the Ecolex IV, but the operating principle had remained unchanged. Typical customers at the time were the Foreign Office, the Department of Defense, NATO and several Danish and German organisations, but the PTT had gradually lost interest in the matter.

Oberman retired from Delft University in 1980 at the age of 70, and passed away on 19 March 1989 aged 78. Of his aprox. 90 patents, about 25% is related to cryptography. A more elaborate work on the Dutch history of cryptographic equipment and its organisation in the post-war era (1945-1970), is the book Staatsgeheim (State Secret) written in 2022 by Oberman's son Maarten.

Quote from the first page of Oberman's book Counting and Counters [II]

  1. Maarten Oberman, Staatsgeheim, De Beveiliging van Overheidsberichten
    State Secret, Government Communications Security (Dutch).
    2022. ISBN 978-9-4644-8870-8.
  1. Digital Circuits for Binary Arithmetic

  2. Counting and Counters
    ISBN 0-333-30512-4. 1981
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Crypto Museum. Created: Saturday 10 August 2019. Last changed: Tuesday, 18 April 2023 - 08:06 CET.
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