thumb|The action of a Caesar cipher is to replace each plaintext letter with a different one a fixed number of places down the alphabet. The cipher illustrated here uses a left shift of 3, so that (for example) each occurrence of in the plaintext becomes in the ciphertext.
thumb|The action of a Caesar cipher is to replace each plaintext letter with a different one a fixed number of places down the alphabet The cipher illustrated here uses a left shift of 3 so that (for example) each occurrence of in the plaintext becomes in the ciphertext