Assuming this is a hobby activity...

If you are considering designing circuitry to solve with ciphers, you need to make one decision before you start:

Are you implementing an exhaustive search through all possibilities, or are you implementing exclusionary sets search?

The first is termed brute force because it generates all solutions with no intellectual shortcuts used in the latter. The former is more straightforward to design, the latter takes a lot of mathematical, automata and process knowledge, much of which is not readily available or if so not readily understandable. :)

If the latter interests you as a hobbyist, I'd recommend doing some online research on Alan Turing's work on the Deutsch Enigma Cipher. You could say that his work was a continuance of the Polish work done before that nation was invaded.

What type of cipher are you planning to experiment upon?

You need to consider too, how your circuit or program will test the value of a iteration's solution. Maybe studying the Index of Coincidence would be a good test if you are looking for language plaintext; you can find this published in many simple, introductory books on cryptanalysis.

It may not impress the professionals, but I've found it fascinating in my hobbyists experiments long ago. Its quite useful in characterizing many pre-computer era ciphers.

If you have a particular cipher in mind, you should open a spread sheet and compute how long you'd need to run in order to get a solutons. If it takes many generations, you're components may not continue to function. :)

Personally, I've lost interest in playing with cipher systems. Before I'd build a bank of ASICs, I'd probably just buy a bank of Pentium 3s instead. Your circuitry will need at least a micro of some sort to decide upon the results.

aka j