The transformation can be represented by aligning two alphabets the cipher alphabet is the plain alphabet rotated left or right by some number of positions. As with all single-alphabet substitution ciphers, the Caesar cipher is easily broken and in modern practice offers essentially no communications security.

The encryption step performed by a Caesar cipher is often incorporated as part of more complex schemes, such as the Vigenère cipher, and still has modern application in the ROT13 system. The method is named after Julius Caesar, who used it in his private correspondence. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. 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. 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. The cipher illustrated here uses a left shift of three, so that (for example) each occurrence of E in the plaintext becomes B in the ciphertext. The action of a Caesar cipher is to replace each plaintext letter with a different one a fixed number of places down the alphabet.

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