How to Solve Substitution Ciphers

What are various methods of solving substitution ciphers.

A substitution cipher replaces each letter in the alphabet with another symbol.

These symbols could be letters, numbers, arcane symbols, lines and dots, and unknown squiggles.

Are you interested in finding out more about ciphers and codes?

The Codebreakers – The Story of Secret Writing book by David Kahn is what I would start with.

Here are 15 tips and techniques to solve any substitution cipher

  1. Scan through the cipher, looking for single-letter words. They are almost definitely A or I.
  2. Scan through the cipher, looking for two-letter words. They are probably IN, OF, TO, IS, AN, ON, BY, BE, IT, and OR.
  3. Scan through the cipher, looking for three-letter words. They are probably THE, YOU, ARE, AND, ANY, BUT, NOT, and CAN.
  4. The most common three-letter words, in order of frequency, are THE, AND, FOR, WAS, and HIS.
  5. If the three-letter word have double letter. It is almost definitely ALL, TOO, and SEE.
  6. The most common four-letter word is THAT. Therefore, if the encrypted word has a pattern of 1–1, it is likely to be THAT.
  7. Look for apostrophes. They are always followed by S, T, D, M, LL, and RE.
  8. Look for common patterns at the end of words. These could be ED, ING, S, and TION. Many words end in E.
  9. Double letters cannot be AA, HH, II, JJ, KK, QQ, UU, VV, WW, XX, and YY.
  10. Count how many times each symbol appears in the puzzle. The most frequent symbol is letter E. Other frequent letters are T, A, and O.
  11. Look for repeating letter patterns. They may be common letter groups, such as TH, SH, RE, CH, TR, ING, ION, and ENT.
  12. Look for double letters. They are most likely to be LL, followed in frequency by EE, SS, OO, and TT.
  13. Look out for names, places and common words, which might occur in the code.
  14. Look out for common phrases at the beginning of sentences. For example, instructions often have sentences starting “YOU MUST…” or “GO TO THE…”
  15. Pencil in your guesses over the ciphertext. If it does not work somewhere else in the code, perhaps your guess was wrong, so try again.

Are you interested in learning how to break codes?

The Elementary Cryptanalysis – A Mathematical Approach book by Abraham Sinkov is what I would recommend.

Now I want to hear from you.

What do you think of the above tips?

Or maybe I missed one of your favorite technique of solving substitution ciphers.

Either way, let me know by leaving a comment below.


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