In cryptography, a classical cipher is a type of cipher used historically but which now have fallen, for the most part, into disuse. Classical ciphers operate on letters or groups of letters and were, in practice, implemented by hand or with simple mechanical devices. By contrast, modern schemes use computers or other digital technology, and operate on bits and bytes. Classical schemes are often breakable in a ciphertext-only attack, and sometimes even without knowledge of the system itself, typically using frequency analysis.

Sometimes classed with classical ciphers are the electromechanical rotor machines, such as the Enigma machine.

See also

• History of cryptography
• ADFGVX cipher
• Affine cipher
• Atbash
• Autokey cipher
• Bifid cipher
• Book cipher
• Caesar cipher
• Hill cipher
• Permutation cipher
• Playfair cipher
• Polyalphabetic cipher
• Running key
• Substitution cipher
• Transposition cipher
• Trifid cipher
• Vigenère cipher