TC-53The TC-53 was the crypto element that was used with the ETK teletype equipment series. It was designed by Dr. Edgar Gretener and produced by Gretag AG in Zurich, Switzerland.
|TC53 with a cover in place at the centre of the front panel. This was the export model.|
|TC-53 with dial installed. This was the model delivered to the Swiss Army. Its name is "Schluessel-Produktions-Geraet" which is the key production device.|
|There are 12 wheels in total. The 4 red ones are scramblers. To the right are the 8 notched wheels.|
|The wheel axle in the swung out position.|
|The 26 fixed, circular contacts at the bottom left are called the "Anschlussplatte" links. They make the contact with the first permutation wheel.|
|All photos and copy in this table via Walter Schmid, HB9AIV|
Walter Schmid provides some theory about the operation of the SPG option.
All the Gretag crypto devices delivered to the Swiss Army were fitted with the SPG dial which is an abbreviation for the German term "Schluessel-Produktions-Geraet," a key production device. It is only a decoder and has nothing to do with the production of the cryptogramm. The SPG decodes 5 bits of the cryptogramm to 1 of 32 alphabetic letters (A - Z; A, E, I, O, U and Y are repeated twice).
What was the purpose of the SPG ?
Each telegramm or transmitting sequence has to be encrypted with a different key. With the Enigma machine, the operator enciphered 6 letters (a pair of 3 random letters) along with the basic key (Tagesschluessel) which was known to every station. The result of the ciphering was a set of 6 letters. They were the first 6 letters of the telegramm. The telegramm itself was ciphered with the 3 random letters and the ciphering was appended to the first 6 letters. The other station deciphered first the 6 letters of the telegramm with the basic key an got the telegramm key twice. With the telegramm formed, position 7 to the end ot the message was deciphered with the telegramm key.
A similar method was used with the Gretag devices. The generator produced a cryptogramm with a length of 26 bits and was a random set. Fourteen bits are used to cipher or decipher the letters; 12 are used to step the 12 wheels of the generator. Only a 1 in the cryptogramm moves the wheels one step forward. The SPG decodes bits 1 to 5 of the cryptogramm and shows as 1 of 32 letters.
How is a key produced?
Station 1 notes a series of 12 random numbers between 1 and 9 (ie 3 5 4 5 9 6 1 8 3 5 7 8) and transmits them in clear to Station 2. Both stations now switch the machine to "key production" mode. The cryptogramm generator was then set to the basic key. Next, the generator was stepped 3 times (the first number). This action steps the SPG assembly to indicate a letter. This letter was written down as the first letter by the operator. Then 5 steps later, the second letter was shown and written down. This process was repeated to the twelfth number. The net result was a series of 12 letters which became the individual telegramm key. Used by the Swiss Army, it took about 10 minutes to produce each new key!
Alternatively, a list with some 100 keys could be used. Each key series was prefixed with a reference number. Station 1 only had to send the reference number (in the clear) to use Key Nr.091 as an example. This was far easier and faster.
To summarize, the SPG is a 5 to 32 decoder. It was used to produce a telegramm key out of a basic key using a set of 12 random numbers. The SPG was not involved with the generation of the cryptogramm.
|Complete SPG assembly including the rimmed, circular bezel. The diameter is 120 mm.|
|SPG with bezel removed. Note that the notched
disks are aligned in such a way that the letter E is visible. This would
be one of 12 letters that the operator would copy down to form the individual
12 digit telegramm key.
Each of the disks 1 - 5 can be moved into two positions, 0 or 1. Therefore, there are 32 possible positions with 5 disks (5 exp 2). At each position one and only one line is visible.
|Rear view of the SPG showing the stepping solenoids needed to rotate the notched disks. Since there were 6 disks, there were 6 solenoids.|
|An oblique view showing the layers of notched disks.|
|This diagram shows the layer assignment for the notched disks. The top disk is the "enable disk" (Abdeckung)|
|This drawing shows the sizes of the notches for each of the disks that comprise the SPG. The notches are of variable width. The thumbnail only shows four of the disks.|
|Logic tree for the 5 to 32 decoder.|
|5 to 32 decoder table. The thumbnail is only showing the first five lines.|
|All photos in this table by Walter Schmid|
Cabling interconnect diagram between the TC-53 and the ETK series teletype equipment. The ETK portion consists of two parts, the ETK-Maschine (teletype device) and the ETK-Verstarker (amplifier with modulator and demodulator). (Image via Walter Schmid, HB9AIV) 1956: (L-R) Power supply for the transceiver, Zellweger Model SE222 HF transceiver, ETK 47 teletype, TC-53 crypto unit and ETK 47 amplifier (modem). The purpose of this configuration was to test ciphered transmissions over short wave radio. It did not work. The cryptogram generators fell out of step very often due to signal fading and interference. After several tests, it was decided to develop a new device, the KFF 58 which could be synchronized. (Photo from the collection of Walter Schmid HB9AIV)
Zellweger AG SE222 Transceiver Specifications
Frequency range: 1.7 to 3.5 MHz
Modes and power output: CW, SSB and F1 modes F1= 100 W, A3a =200 W; A1=100 W.
Primary power: 92 - 292 Volt
Production Years: 1956 – 1963
Dimensions (WHD) 420 x 380 x 310 mm / 16.5 x 15 x 12.2 inch
Net weight: 26 kg / 57.3 lb
Comment: About 550 SE222's were delivered to the Swiss Army.
Contributors and Credits:
1) Walter Schmid <hb9aiv(at)swissonline.ch>
2) SE-200 specs