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Ecolex IV
One-Time Tape cipher machine - under construction

Ecolex IV was an online/offline One-Time Tape (OTT) cipher machine (mixer) for teleprinter communication, developed and built by Philips Usfa in Eindhoven (Netherlands). It was introduced in 1963 as the successor to the Ecolex-II and was a further development of the Ecolex II/B and Ecolex III. Ecolex IV was the first transistorized mixer that featured built-in synchronization. The machine is also known as Ecolex 4, and by the internal Philips Usfa designator Us 8015.

If the cipher tape consists of truely random numbers, the cipher is unbreakable. Sometimes however, a pseudo-random number generator was used to create the cipher tapes, making it less secure.

The image on the right shows part of an Ecolex-IV. The top half of the image shows the controls. Below that are the two punch tape readers. The one closest to the control panel is for the cipher tape, whilst the other one is used for the clear-text tape. More and better photographs will be presented here as and when they become available.

Rear panel
This is the rear panel of the Exolex-IV. Please note the white telex connector at the centre of the image, mounted on a sub-assembly. This allowed the machine to be delivered with a variety of connectors, such as the Siemens Telex connector shown here.

In most cases, the machines had two 6 mm jacks for connection to a telex-line or a radio modem. The Ecolex-IV can be used on both 2-wire and 4-wire telex networks.

The machine is extremely heavy and is mounted on 4 springs, probably to guarantee smooth operation in a vehicle. The interior of the machine is filled with so-called 'functional blocks'; small encapsulated electronic circuits, that can be regarded as the predecessors of Integrated Circuits (ICs).

This image shows a close-up of the two paper tape readers. The rear one was used for the cipher tape. It has a small integrated knife at the left, that destroys the cipher tape immediately after use. This was done to prevent the tape from being used again.

The front tape reader was used for the clear-text tape. At the right it has a special bracket with an ingegrated switch. The clear-text tape had to be fed through this bracket, so that the machine would stop once the source tape had finished.

Front panel of the Ecolex-IV Rear panel of the Ecolex-IV Paper tape readers of the Ecolex-IV
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Front panel of the Ecolex-IV
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Rear panel of the Ecolex-IV
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Paper tape readers of the Ecolex-IV

Development of the Ecolex-IV was started in 1959 at the newly erected Philips Usfa building Schouwbroekseweg in Eindhoven (Netherlands), shortly after the PTT-designed Ecolex-II had been taken into production. Although the Ecolex-II was perfectly adequate, the Dutch Army wanted a machine with built-in synchronization that could be used reliably over radio.

In the years between 1959 and 1963, a number of experiments were carried out and several prototypes were designed, such as the one shown on the right. In this case the existing Siemens tape reader (also used with the Ecolex-II) is used, mounted on top of the prototype.

Clearly visible in the picture are the two counters that were used to count characters from the key tape whilst synchronizing. Similar counters are present on the final Ecolex-IV design, as it is visible above, and on other prototypes.

It is believed that this variant was submitted to SECAN as the Ecolex II B, in order to get NATO approval. After several recommendation and improvements were implemented, the Ecolex IIB was approved on 19 November 1959 for NATO traffic of all classifications [3]. It is likely that this was machine was internally known as Ecolex III, but that it was never taken into production.

 Check out the Ecolex III
Early Ecolex-IV prototype

The Ecolex-IV was developed between 1959 and 1963 and approximately 750 units were built. In the late 1960s, about 150 units were modified with the so-called Tarolex pseudo-random key generator. The machine remained in service until the mid-1970s when they were gradually replaced by the Ecolex-X. The Ecolex-IV was a very reliable machine with a very low failure rate.

Ecolex IV was sold to the Dutch Army, Navy and Air Force and also to most other NATO countries after winning a NATO evaluation.

Early Ecolex-IV prototype
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Early Ecolex-IV prototype

The operating principle of the Ecolex-IV is identical to other cipher machines in the mixer class. At present, it is unclear whether the Ecolex was able to exchange messages with other mixer machines, such as the Siemens M-190. The Ecolex-IV service documentation suggests that it is compatible with mixer machines used by other NATO countries, but to date we have not been able to verify this.

Like most cipher machines of the mixer-class, the Ecolex-IV is not (and never was) classified. It is the combination of the machine and a NATO-issued cipher tape, that was classified as NATO SECRET. Because of the fact that one-time tapes (OTT) were used with the Ecolex-IV, it is impossible to use the machine to break old intercepted messages, as all original OTP-tapes were destroyed per protocol immediately after use. Unfortunately, not many Ecolex-IV machines have survived and they are rarely seen in museums.

  1. Philips Usfa, Internal photographs of Ecolex IV development
    Crypto Museum Photo Archive. CM300635.

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

    SGM-660-59. 19 November 1959. NATO SECRET.
    Declassified by NATO on 5 January 2000 (IMSM-431-99).
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Crypto Museum. Created: Friday 14 June 2013. Last changed: Saturday, 24 February 2018 - 15:29 CET.
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