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Reichert Elektronik 5224
Key Tape Perforator - wanted item

The 5224 was one of the first Random Key Tape Perforators, produced by Reichert Elektronik in Trier in the early 1950s. The machines were intended for the production of key tapes for the so-called mixers: telex-based cipher machines with truely unbreakable One-Time Pad encryption.

The machine is based on the principle that One-Time Tape (OTT) encryption requires two identical key tapes (no more and no less). By punching the two tapes simultaneously, they are guaranteed to be identical. By installing a set of (optional) counters, the randomness of the generated key can be checked.

The image on the right shows a typical 5224 machine as it was used for many years by the Austrian Army. The noise generator, which is normally present at the bottom left, is missing from this unit as it was used in a cascased setup.
  

After Germany joined NATO in 1955, it became increasingly difficult for Reichert to sell highly secure equipment to countries ourside of Europe and NATO. As a result, the company was moved in 1967 to the neutral country of Austria, where they settled down in the town of Mils. The company was renamed Mils Elektronik and its first product was the successor of the 5224: the Mils A-6723. It was nearly identical to the 5224, but had a slightly more modern colour.

Front view of the 5224 Close-up of the counters and the control panel Printer, reader and puncher Tape puncher Optical tape reader (closed) Index printer Connections at the left side

2134 Optical Tape Reader
The 5224 contained the propretary 2134 optical tape reader tat was built by Reichert as a replacement of the mechanical tape readers (e.g. from Siemens) that were commonly used in those days. As the unit has no moving parts, it is less sensitive to mechanical problems.

The unit consists of two parts. The upper part is hinged and constains a lamp the illuminates the tape and shines through its holes. The lower part contains five light-sensitive diodes, or photo-diodes, that are fast enough to follow the rapidly moving tape. The signal from the photo-diodes is then converted to the appropriate level using transistor amplifiers mounted in the lower part.

The image on the right shows the opened tape reader, with the (yellow) tape properly inserted in the tape gutter. Behind the tape, the cable to the lamp in the top section is just visible.
  
Optical tape reader (open)

When the unit is closed, the tape is 'trapped' inside the gutter so that it can't move sideways. The tape reader can be opened again by pressing the red button at the front and folding away the top section. The full service documentation of the 2134 is available for download below [2].

Optical tape reader (closed) Optical tape reader (open)

Mixer machines
The random key tapes produced by the A-6723 are suitable for use with virtually any type of telex-based mixing cipher machine (mixer), such as the Siemens T-43, the ETCRRM (used on the America-Moscow Hotline), the Hagelin TC-52, the Siemens M-190, the Philips Ecolex 4 and Mils' own mixers like the ME-640 and the ME-840. For a complete overview, click here.

<i>Mixing of the <b>plain text</b> and the <b>key</b></i>

The above illustration explains how a mixer works. Eacht letter from the Plain-text is added to a letter from a key tape, using an exclusive-OR (XOR) operation (sometimes called 'module-2 addition). The advantage of this operation is that it is reversable: adding the key stream to the cipher text, reveals the plain text again. The A-6723 is used for generating the red (key) tapes. For a detailed description of this principle, read our page about the Vernam Cipher.

References
  1. Mils Elektronik, A-6723 Sales Leaflet
    Date unknown, but probably late 1960s. 1

  2. Reichert Elektronik, Fotoleser 2134
    Date unknown. Retrieved July 2013.
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