Hi, We have a ciphertext with IC=0.0685. We want to find out the class descriptor (mono-alphabetical/poly-alphabetical/transposition). I have applied the 2 probabilistic tests to try and guess what class it belongs to. These tests are:
- Ratio of vowels to total (<25%) then more likely a substitution
- %ETAOS in text (<35%) then more likely a substitution
and i have found 31% for vowels and 18% for %ETAOS.
I know that these tests don't guarantee success.
IC value ranges from 0.0384 for polyalphabetic ciphertexts with a perfectly flat distribution, to 0.068 for a monoalphabetic ciphertexts, from common English.
What should my answer be? Is it a transposition or a monoalphabetic cipher? (I have excluded the polyalphabetic answer according to what I wrote above.)