Guesses which cipher or encoding produced a text from its characters and statistics, with the reasons and the tool to try next.
Procedure
How it works
Before breaking a cipher you need to know which one it is. The character set is the first clue: only 0 and 1 means binary, dots and dashes mean Morse, the digits 1 to 5 in pairs suggest a Polybius square, two letters in groups of five a Baconian cipher, the letters A D F G V X the ADFGVX cipher, and a mix of cases and digits with = at the end Base64.
For letter ciphers the statistics decide. If some Caesar or affine key makes the text English, that is the answer. Otherwise the index of coincidence tells one alphabet (about 0.066) from several (lower): with English letter counts but no English order it is a transposition; with an English IC but foreign counts a substitution; with a low IC and English-like columns at some period a Vigenère cipher. Playfair leaves its own marks: an even number of letters, no J, and never two equal letters in a pair.
The confidence numbers are rules of thumb, not probabilities, and short texts can fool any rule. The tool to try next is named for each candidate.
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