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There's a code I'm trying to decipher. What I know is that it's a simple substitution, with just a few added rules intended to make frequency analysis and other very common methods a little less efficient.

I know for example that:

  • there is no letter repetition, so there must be a way to code double letters (there is no spaces either so you can't just delete double letters)
  • there is more than 1 character that for the letter 'e'.
  • there are more rules. (I don't know how many but it's supposedly "very simple". All rules can be applied by head easily, without needing a chart, a grid or anything else.)

I can ask for data, but the challenge is to decipher it with as little data as possible.

My question is, is it possible to use a classical frequency analysis (like quipqiup) with increased "tolerance"? (provided I have enough data) Or do I necessarily have to hard-code every possible rule there could be in a custom algorithm?

Basically, how far would I have to go from a classic frequency and bigram/trigram analysis algs to crack the code without having to know all the rules?

I have no idea how to approach this but I refuse to think simple rules on top of a substitution can render all classical analysis useless.

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  • $\begingroup$ I'm sure breaking this type of encryption is possible. Mary Queen of Scots had a similar cipher and someone broke it easily. But, I'm afraid there isn't a tool for this type of encryption. $\endgroup$ – Neo1009 Oct 1 '19 at 23:47

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