Relative Frequencies of Letters in the English Language Graph

This method of creating secret messages is not very secure.

Short messages can be deciphered by just applying all 25 possible shifts and reading the output; longer ones can be attacked by a method known as frequency analysis.

The distribution of letters in an average sample of English text has a predictable shape which is easy to determine. The Caesar cipher shift also shifts this distribution, and it is easy to determine the shift by analysing the resultant frequency graph.

We look for the most common letter in the message and assume this must correspond to the most common letter in the English language, e.

This gives us the shift and we can now read the message.

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