I have the following ciphertext that I want to decipher:
bnmkogt vgyhni uioopkm xswercvdf yuiogvbnm ghjy cftyhng tgeyjn xdrtygvc zsefx xdrgbhu tgbnmko tgbnmhyui yhnmko vbnmgyuiok
So far, what I have done:
- Perform a frequency analysis. This suggests that no transposition cipher was used. I Also try all 26 ROT combinations for substitution cipher with no results.
- Move to polyalphabetic ciphers. My first option is Vigenere. In that context I found that there are several trigrams , bnm, repeated and two 5-grams, bnmko, (which is probably not random and indicates that the same text is encrypted with the same part of the key).
- I use the only 4-letter-word of the text, GHJY, and compare it with the most common four-letter words in English (assuming it is English...), with no good results.
- I measure the distance between the 5-grams and found that is 72, which factors are 1,2,3,4,6,8,9,12,18,24,36.
- I also ran an Index of Coincidence analysis which suggests that the key length is 7.
I think that I'm missing something. Any thoughts/ideas on how can I better address this cryptogram? What would you do? Thanks!
PS. The only clue of the cryptogram says "Manual work". Apparently, it is a classic cipher...