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I have read some documents to decrypt ciphertext without a key using Frequency analysis. here are my questions:

  • If the most occurring Char is not 'E' then how do we start?
  • Let's say I have this ciphertext

    MLD BLF PMLD GSV TZNV SLD GL KOZB RG. TVG IVZWB ULI HRNROZI KILYOVNH RM BLFI VCZNH. XSVVIH.

Here is its decrypted text: now you know the game how to play it. Get ready for similar problems in your exams. cheers

can someone please help me to sort this out, here most occurring is 'L' but it is not 'E'. 'L' is 'o' here ... I am very confused.

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This is a monoalphabetic substitution cipher - the same letter in the plaintext will always be represented as a identical letter in the ciphertext (for example the plaintext-letter "E" is always a "V" in the ciphertext).


Frequency analysis works better the longer the text is. For very short texts (as yours) it can be very difficult to have an exact representation of the frequency analysis. If the most occuring letter is not "E", then you can move on to the second-most common letter (which would be the letter "T")

Other / similar techniques:

  1. Double-letter-words: Another technique you could try is to find all the words that have repeating letters, for your example that would be the last word "cheers". I think that in the English language the most common double-letter-words have 2 "L" in them, like "kill". But again this would fail, since here the double-letter-word is "cheers".

  2. Word-frequency-analysis: You can also do a frequency analysis for whole words instead of single letters. Again, for the English language, this would be the word "the". For a long text you would expect that the word "the" would show up most often.


As you can see most of these common techniques would fail for your cipher-text. So the best technique you can use is brute-force.

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    $\begingroup$ It's not a Caesar shift: if E goes to V, F has to go to W, but W is a plain D here. $\endgroup$ – Henno Brandsma Feb 19 at 8:59
  • $\begingroup$ Thanks for the comment, I corrected the answer. $\endgroup$ – AleksanderRas Feb 19 at 9:27

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