[Cryptography] Hypothetical WWII cipher machine.

John Ioannidis ji at tla.org
Sun Jul 19 15:49:19 EDT 2015

On Sat, Jul 18, 2015 at 1:56 AM, Ray Dillinger <bear at sonic.net> wrote:

> ...
> He asked me for a detailed design for something that (A) could
> realistically have been built around WWII, (B) is not a rotor
> machine, (C) is very much more secure than Enigma, (D) that he
> could do a cool, interesting, understandable illustration of,
> (E) whose basic operation could be explained in one page or
> less, and (F) would not make real cryptographers laugh if they
> read his book.

a possibly implied requirement that you do not state is that the device be
about as portable as the enigma. Is it?

If your communication requirements are, for example, between a land station
an a U-Boat, the device doesn't have to be so small.

The LFSR parts of A5/1 can easily be implemented with relay logic, and
Vernam's design from his1919 patent can be used to combine it with the data

the hardware requirements to cryptanalyse A5/1 are definitely beyond the
capabilities of 1940s technology.


You can use relay logic / ladder logic and crossbar switches to implement a
feistel cipher
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