breaking ciphers

In a substitution cipher a message is encrypted by replacing its letters with code letters, for example replacing every ‘a’ with ‘g’, every ‘b’ with ‘w’ and so on for every letter of the alphabet.

The readable message is called the the plaintext and the encoded message the ciphertext.

Breaking a cipher is fun but challenging. It’s supposed to be challenging. Here’s a good way to start:

1. Count how many times each letter occurs in the ciphertext. This has been done for you in the example below using the Colab script.
2. The most common letters in English are often E, T, A, O, N, R, H, I and S. Make the educated guess that the most common letter in the cipher text represents ‘E’, the next most common represents T and so on.
3. Underline repeated patterns in the cipher text, for example if you see the pattern AFV repeated often it probably stands for a common 3-letter word like ‘and’ or ‘the’.
4. In English only certain letters can be repeated, ‘ee’ as in ‘see’, ‘oo’ as in ‘school’, ‘ll’ as in ‘hill’ etc. Underline these and come back to them occasionally to see if you can figure them out.
5. Any information about the content of the message is extremely useful; if it’s a letter the first work might be ‘dear’ for instance.

Hint: Not the worst way to start a book.