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In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques.

It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet.

For example, with a shift of 3, < tt > A </ tt > would be replaced by < tt > D </ tt >, < tt > B </ tt > would become < tt > E </ tt >, and so on.

The method is named after Julius Caesar, who used it in his private correspondence.