I recently got a file which I had encrypted with substitution cipher a long time ago.

I went to crack down the key and almost got it.

But I encrypted it not just with alphabets but also with numbers as well.

I checked online for a substitution cipher encoder/decoder, but didn't found any.

I know the algorithm: Substitution Cipher

I know the key: Alphanumeric (Like A=1, B=F, C=5 and so on)

I have the cipher text

Is there any site or code implementation where I can decode the message with an alphanumeric key?

P.S. If this is not apt question here (security section), please let me know where should I ask this.

  • just try all 36, one will be readable
    – dandavis
    Aug 27, 2017 at 21:50

1 Answer 1


You should be able to crack it with some simple statistics analysis, using common patterns of english language. For example the word 'the' or 'is' will appear frequently and same word would appear the same in different locations of the ciphertext.

After obtaining the key, you can probably write a simply script or program to 'decrypt' the message. I wrote a Ruby function that will do this

table = { 'a' => 1, 'b' => 'f' ... }
def decode(msg, table)
  msg.split("").each { |a| table[a] }.join("")

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