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The Fialka was an electromechanical rotor machine.

How does the Fialka manage to have a letter encipher unto itself? I realize it does something clever by using transistors, but it has a reflector. With direct current circuits, there has to be a negative and a positive connector. If one simply attached a positive current to itself, it wouldn't flow. So, how does it work?

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The Fialka (ФИАЛКА; M-125) does have a reflector, but it operates via a "magic circuit" that allows a letter to be encoded to itself, unlike the Enigma.

The use of a reflector makes the machine symmetrical, which means that the same settings can be used for encoding and decoding. A major drawback however, is that a letter can never be encoded into itself. This was considered a serious weakness of the Enigma cipher machine.

In the Fialka, this is solved by adding a clever electronic circuit to the reflector, to ensure that a letter can be encoded into itself. This is done by taking 4 wires out of the reflector (i.e. two pairs). One of these wires is used as the 'letter-can-be-itself' signal and is sent back to the keyboard. The remaining three wires are combined into a binary rotator. In the German Fialka literature, this circuit is called Dreipunkschaltung (three-point circuit), but we have dubbed it 'Magic Circuit'.

The M-125-3 version of the Fialka is quite sophisticated: it had a card reader that took the place of the Enigma's plug board, with the current passing the card reader twice, but it provided a stronger permutation. According to the website you quoted, the FIALKA remained in service in some areas until the 1990s.

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The reflector wheel on the Fialka incorporates a transistor switching circuit connecting pins 16, 18 and 24. In coding mode, a signal on pin 16 is connected via pin 18, a signal on pin 18 is connected to pin 24, and a signal on pin 24 is connected to pin 16. In decoding mode, these paths are reversed. This allows the Fialka to encode any letter as itself, overcoming one of the major weaknesses of the Enigma machine.

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  • $\begingroup$ What I am asking is more of an element of circuit design. How does it do it without causing a short circuit? $\endgroup$ Nov 28 '16 at 21:08

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