I am trying to break a harmless ciphertext that uses a monoalphabetic substitution cipher.(adsbygoogle = window.adsbygoogle || []).push({});

The ciphertext is exactly 244 characters long, without any spaces between words. It consists only of uppercase letters.

ciphertext = "JGRMQOYGHMVBJWRWQFPWHGFFDQGFPFZRKBEEBJIZQQOCIBZKLFAFGQVFZFWWEOGWOPFGFHWOLPHLRLOLFDMFGQWBLWBWQOLKFWBYLBLYLFSFLJGRMQBOLWJVFPFWQVHQWFFPQOQVFPQOCFPOGFWFJIGFQVHLHLROQVFGWJVFPFOLFHGQVQVFILEOGQILHQFQGIQVVOSFAFGBWQVHQWIJVWJVFPFWHGFIWIHZZRQGBABHZQOCGFHX"

I have come up with the probability distribution of the letters. The ratio indicates the probability of that letter.

Letter: F Tally: 37 Ratio: 15.163934426229508

Letter: Q Tally: 26 Ratio: 10.655737704918032

Letter: W Tally: 21 Ratio: 8.60655737704918

Letter: G Tally: 19 Ratio: 7.786885245901639

Letter: L Tally: 17 Ratio: 6.967213114754098

Letter: O Tally: 16 Ratio: 6.557377049180328

Letter: V Tally: 15 Ratio: 6.147540983606557

Letter: H Tally: 14 Ratio: 5.737704918032787

Letter: B Tally: 12 Ratio: 4.918032786885246

Letter: P Tally: 10 Ratio: 4.098360655737705

Letter: I Tally: 9 Ratio: 3.6885245901639343

Letter: J Tally: 9 Ratio: 3.6885245901639343

Letter: R Tally: 7 Ratio: 2.8688524590163933

Letter: Z Tally: 7 Ratio: 2.8688524590163933

Letter: E Tally: 4 Ratio: 1.639344262295082

Letter: M Tally: 4 Ratio: 1.639344262295082

Letter: A Tally: 3 Ratio: 1.2295081967213115

Letter: C Tally: 3 Ratio: 1.2295081967213115

Letter: K Tally: 3 Ratio: 1.2295081967213115

Letter: Y Tally: 3 Ratio: 1.2295081967213115

Letter: D Tally: 2 Ratio: 0.819672131147541

Letter: S Tally: 2 Ratio: 0.819672131147541

Letter: X Tally: 1 Ratio: 0.4098360655737705

Letter: N Tally: 0 Ratio: 0.0

Letter: U Tally: 0 Ratio: 0.0

Letter: T Tally: 0 Ratio: 0.0

Since I haven't taken much statistics, I'm not sure how I would set up a chi-square test to solve this problem but my cryptanalysis text says that a program using a chi-square test would be essential to solve this problem in the most efficient way possible.

Perhaps someone could help me with the chi-square? Or perhaps someone could help me with a few letters of the key using their knowledge of English?

I don't necessarily care about solving the problem efficiently, I would just like to know what the cipher text comes to.

Progress so far:

E --> F --> E

T --> Q --> T

H --> G --> H

Thanks!

BiP

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# Cracking a monoalphabetic substitution cipher

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