Electronic Teleprinter Cryptographic Regenerative Repeater Mixer (ETCRRM)

Produced and trialed  in 1958, this machine uses the Vernam stream cipher method (circa 1919) in which plain text message is eXclusively OR'ed with a random or pseudo random stream of data of the same length to generate the ciphertext. Once a message was enciphered the keytapes were were destroyed. At the receive end, the process was reversed. An identical keystream tape was used to decode the message.  Internally the machine uses mainly 12AT7 tubes, several 6CH6's relays and selenium diodes for implementing logic functions. The machine was designed for low speed, start-stop asynchronous applications in conjunction with a  teleprinter, reperforator or T-D (Transmitter-Receiver) as an input or output device. Highly succesful, its main users were the Royal NAvy and NATO. 

ETCRRM was used for high level communications at military headquarters or tape relay centers.  Four ETCRRM's were used on the Washington/Moscow Hotline when it was first installed on 1963. This machine is held by the C&E Museum in Kingston.  (Photo by Jerry Proc)

etcrrm_pristine_01a.jpgThis is the example of the ETCRRM held by the National Cryptologic Museum (NSA photo) .

The engraved dedication plate on the machine reads as: 
Presented to National Security Agency by Chief of Defense Security Norway Brig Hans Dramstad 02 May 1996 

etccrm_2.jpg This ETCRRM example used by NATO was produced by the Norwegian company Standard Telefon og Kabelfabrik A/S. The nameplate reads: 

45/50 baud
115/230 volt AC 50/60 cps

The keystream tape was supplied from a spool at the left of the machine. It fed to the right, across the reader head and into a bin .

It was used as late as 1984 in Denmark on low priority teletype circuits. (Copy and photo by Henrik Teller)


The cryptographic unit is a component of the ETCRRM and requires no motor for operation. The mechanical drive for the keystream tape reader was provided by a solenoid and ratchet system. A built-in regenerative circuit regenerates the incoming signals and provides a low distortion output. The element timing is controlled by a start-stop inductance-capacitance oscillator and the character timing is achieved by means of a three stage binary counter circuit. The device did not have an internal power supply to provide the loop current. That had to be provided externally.


Operating Speeds

* 45 baud (60 wpm or 368 operations per minute).
* 50 baud (66 wpm or 404 operations per minute).

Current Loop : 20 ma. or 60 ma.
Power Consumption : 110/240 volts AC,  45-60 Hz. 60 watts.


a) Cipher-Text Key - A three position non-locking telephone type key with positions Cipher and Text. In the Cipher position, it places the machine in a condition to send or receive enciphered text. In the TEXT position, it sets the machine to send or receive plain text messages.

b) Break/Release Key - A three position non-locking telephone type key with positions Break and  Break Release. When thrown in the Break position, it creates a steady spacing condition which breaks the operation of the distant station. In the Break Release position, it releases or unlocks a break which has been received by the local station.

c) Station Test-Local Key -  A three position non-locking telephone type key. When placed in the Station Test position, it places the local station in a condition to be tested without interference from the line. Moving the key to Local Test provides a means of testing the local teleprinter without passing through the operating circuits of the ETCRRM. The center position of the key provides a circuit path for operation of the station in Text or Cipher mode.

d) Power Supply Switch - Turns the machine on and off.

e) Test Reduced Voltage Switch -  This reduces the power to the unit by a factor of 10%.

f) Test Check Circuit Switch - Has an OFF/ON position. Normally ON. When switched to OFF, a fault is placed in the internal circuits to check the break feature.

Above and below: Enlargements showing front panel controls and indicators. 
This version of the machine has two fuseholders on the front panel and a voltage nameplate . It is suspected the fuseholders were moved to the front panel for the convenience of the operator.
All photos in this table by Jerry Proc
This pristine ETCRRM example is held by the Military Museum in Vienna, Austria. It is not known why the tape reader has been detached from the main unit. Note what appears to be four fuses in the lowest portion of the font panel and the four indicator lights in the uppermost front panel - yet another minor variant. 

a) Local Current Switch - Alters the operation of internal circuitry depending if the machine is used on 20 or 60 ma current loops.

b) Speed Control Switch - A two position multi-control switch which is used to select the line speed. (ie 40 or 50 baud)


Bryan Garland, who trained on this machine, recalls. "A Creed teleprinter was connected to the     ETCRRM. Two identical,  randomly punched tapes containing the keystream  were provided by the National Security Agency - one for each end of the circuit.  These could only be used once, then had to be destroyed.  Both had index numbers printed on the tape and these were highlighted. The index number was exchanged in the clear with the far station. Next, the keystream tape would be lined up in such a way that the highlighted index number on the tape was right over top of the tape reader pins. Following that, the gate was clipped down on the tape reader and the operator would switch to Cipher mode. This caused  the inputted typing be encrypted by logically combining the Baudot characters with those on the keystream tape.

At the receiving end, the process was reversed.  The operator would set his machine to decipher and the plain text would be printed on the Creed Teleprinter".

This is an example of the chadless tape output from a Creed reperforator. (Tape supplied by Bryan Garland) 

etcrrm_training_manual_s.jpg (Click on image to enlarge). This was the ETCRRM maintenance training manual. It contained no cryptographic information and only enough of a schematic diagram to illustrate the principles of operation. Including the time spent on electrical fundamentals, the total allotted training time was 120 hours. Of this, 100 hours was devoted to the machine itself. CINCENT was the French Signals School in Montagis, Loir et Cher, France. (Manual provided by Bryan Garland)
Closeup of paper tape reader. Note that only the cipher tape passes through the reader. It's output was XOR'ed with the data stream coming from the line input. The tape  reader was made by Creed & Company of Croydon, UK.
Left side view of chassis. 
Right side view of chassis. 
Chassis rear view. If anyone is in search of "patina" this particular example sure has enough of it. 
All photos in this table by Jerry Proc

Mo Davies indicates the following. " Incidentally, I was also involved with the only mobile NATO comm centre before being detached to JHQ.  28th Signal Regiment provided the facility using box-body wagons.  In about 1964, it was found that modern test equipment could detect the plain language on the line as "spikes" riding upon the encyphered signal.

The ETCRRM internal circuits were modified to use "dry keying", which removed the problem.  The Seimens T100 printer, T68 printing reperforators, and Seimens tape readers had the filters removed, which allowed the dry keying to operate as advertised.  However, due to budget constraints, after modification, the Seimens equipment was withdrawn.

We "bummed" cast off Lorenz (LO15?) printers, and Lorenz non-printing perforators and readers from the RAF, who had decided to scrap them due to unreliability.  We then spent a year proving that the Lorenz equipment was not compatible with dry keying in the ETCRRM! "

Contributors and Credits:

1) David Wallace
2) Henrik Teller <henrik_teller(at)vip.cybercity.dk>
3) Bryan Garland <bgarland38(at)hotmail.com>
4) ETCRRM  Maintenance Training Manual
5) Communications and Electronics Museum,  Kingston Ontario.
6) Mo Davies <modavies(at)ntlworld.com>

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Aug 1/10