Letter Frequency Analysis


This page analyzes a text’s letter frequency and is an emulation of Tyler Atkin’s page. One application is decoding a Caesar cipher. A Caesar or “shift” cipher is an encryption technique in which each letter in the unencrypted message is shifted over a certain number of positions. For example, A encodes into B and B into C. The cipher is named after Julius Caesar who reportedly used a shift cipher of three to communicate with his generals.

So how do we break a Caesar cipher? One technique is to analyze its letter frequency. In English, certain letters like E and T occur more frequently than others like Q and Z. By getting the shape of the letter frequency distribution and comparing it to the known relative letter frequencies of the English language, we can sometimes determine if a Caesar cipher was used.

Enter text into the box below to see its letter frequency. Click the plus and minus signs to alter the plaintext by changing the amount the alphabet is shifted. [Click here][3] for a demo.


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Shifted plaintext