Ciphers

How do classical ciphers work?

The need to conceal information grew with government, diplomacy, trade and warfare. Rulers and commanders wanted intercepted orders to remain unreadable. Early methods had to work without machinery, so they substituted symbols or rearranged the letters of a message.

A single substitution eventually became too predictable. Vigenère used multiple alphabets, the Polybius square represented letters as coordinates, and transposition ciphers concealed natural word order. Telegraphy and radio increased message traffic, leading in the twentieth century to rotor machines such as Enigma that changed the substitution automatically.

Cryptanalysis evolved alongside cryptography. Letter-frequency analysis broke simple substitutions, repeated fragments weakened polyalphabetic systems, and faster computation made many historical designs obsolete. Competition between code makers and code breakers pushed encryption toward increasingly mathematical methods.

Modern algorithms such as AES‑256‑GCM process binary data, use enormous key spaces and can detect a modified message. Classical ciphers remain valuable because they clearly demonstrate keys, substitution, transposition and the difference between merely disguising information and protecting it securely.