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EROLET   Us 8503
Key-tape generator - wanted item

EROLET I was a Random Number (Noise) Generator (RNG), developed by the Dutch Post Office Laboratories (PTT, Dr. Neher Lab) 1 and built by Philips Usfa in 1955. It was used for the creation of the One-Time Tape (OTT) punched paper tape pairs for the Ecolex-I and other one-time tape cipher machines (mixers). The name EROLET is short for Electronic Roulette. The machine is also known as Us 8020. According to an internal Philips memo of 1982, only 10 units were built [2].

The machine is housed in a large metal case, probably 19" wide, with metal carrying handles at the top. The ON/OFF switch is located on the small control panel at the lower centre. A nearly identical enclosure was used for the Ecolex I cipher machine, which was built in the same era.

By using a random number generator (RNG) for the production of 5-level baudot key tapes, the machines using them -commonly called mixers- can provide an unbreakable cipher. The data from a key tape is generally known as the key stream and is mixed with the plaintext by means of the mathematical modulo-2 or XOR operation. This operation is known as the Vernam Cipher.

Although random number generators were also available from other manufacturers, such as Reichert Elektronik, the Dutch Government wanted a machine was not flawed and could not be manipulated, and tasked the PTT Labs in The Hague with the development of the EROLET I.

The image above shows the Us 8503 random number generator with the optional Us 8903 checking unit or counter. The latter consists of 33 counters, 32 of which are used to count the occurencies of each of the 32 possible binary values (25) . If the system produces truely random noise, the data should be evenly spread and the counters should all have a nearly identical value after several hours of operation. The counters are numbered 0-31. The extra counter at the bottom shows the total number of characters that have been produced since the last reset.

Power was provided by a separate Power Supply Unit (PSU). The EROLET was developed by the PTT in 1954/55 and was taken into limited production by the Dutch defence contractor Philips Usfa in Eindhoven (Netherlands) in 1955. Between 1955 and 1959, no more than 10 units were built [2]. They were used by the Dutch Government, but also by the Governments and Armies of other countries like Denmark [3]. As far as we know, there are no surviving examples of the EROLET.

  1. At the time, the PTT was the Dutch state-owned telecom monopolist.

EROLET with counter box
Close-up of the counters
Power Supply Unit
Double tape puncher
Mils double tape puncher
The EROLET was capable of producing random 5-bit characters at speeds of 45.5, 50, 75 and 100 baud. The the default speed of 50 baud, this means that approx. 400 characters are generated per minute. The EROLET can produce all possible binary value 0-31, or can be limited to any subset by means of the switch panel. The circuits are suitable for 40 mA and 60 mA current loop.

The simplified block diagram above shows how the EROLET works. At the top left is the noise generator, for which a 'noisy' triode was used. This noise signal is used as the basis for the generation of the random bit values. The output is at the bottom.

Key tape production
A good way of producing two key tapes simultaneously, is by using a double tape puncher as produced by Reichert Elektronik 1 in Trier (Germany). As a crypto manufacturer, Reichert was specialised in One-Time Pad (OTP) and One-Time Tape (OTT) paper punching solutions.

The double tape puncher is shown in the image on the right. Blank tapes are entered into the puncher at the right, where the two reels are mounted horizontally. Both tapes are lead through the same tape puncher, so that both copies are identical. Once punched, they are spooled onto two empty reels at the left.

Reichert (and later his successor Mils) 1 also developed double tape punchers with a built-in random number generator. An example of that is available on our page about One-Time Tape.

The machine shown above was used around 1959 at Philips Usfa for the production of key tapes. Although the Reichert tape duplicator with built-in noise generator, was probably just as good as the EROLET developed at the PTT, the Dutch Government wanted to avoid the possibility of being manipulated and only trusted national production. It was the only way to guarantee security.

  1. In 1965, Reichert moved his company to neutral Austria and renamed the company to Mils Elektronik. For this reason, the above machine is also known as a Mils Machine. Mils Electronic is still in business today.

The complete EROLET system was designated Us 8020 and consisted of the following components:

  1. Us 8503/00
    Random Number Generator
  2. Us 8501/00
    Power Supply Unit
  3. Us 8502/00
    Cable bewteen (A) and (B)
  4. Us 8902/00
    Counter 1
  5. Us 8903/00
    Cable between (A) and (D) 1
  6. Us 8901/00
    Tuning Fork 125 Hz 1
  1. Optional device (recommended).

  1. Philips Usfa Erolet I, type nr. Us 8020
    Operating instructions (English). 6 December 1955.
    Retrieved February 2016 from [3].

  2. Gebrauchsanweisung fur den Philips Usfa Zufallsgenerator EROLET I Typ.Nr. Us 8020
    Operating instructions (German). 7 February 1958.
    Retrieved February 2016 from [3].
  1. Photographs from Philips Usfa
    Crypto Museum Archive.

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

  3. Anonymous contributor
    Personal correspondence. February 2016.
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Crypto Museum. Created: Monday 13 June 2016. Last changed: Tuesday, 07 July 2020 - 16:48 CET.
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