Explore classical substitution ciphers that replace characters with other characters.
Substitution ciphers are among the oldest encryption methods, where each character in the plaintext is replaced with another character according to a fixed system. While not secure by modern standards, they provide excellent educational value in understanding cryptographic principles.
Simple shift cipher where each letter is replaced by a letter some fixed number of positions down the alphabet.
Polyalphabetic substitution cipher using a keyword to determine shift values for each position.
Mathematical cipher using modular arithmetic: E(x) = (ax + b) mod 26.
Monoalphabetic substitution cipher where A→Z, B→Y, C→X, etc. No key needed.
Special case of Caesar cipher with a shift of 13. Self-inverse (encrypting twice returns original).
Digraph substitution cipher using a 5×5 matrix of letters based on a keyword.
| Cipher | Key Type | Security | Era | Complexity |
|---|---|---|---|---|
| Caesar Cipher | Number (0-25) | Very Low | ~100 BC | O(n) |
| Vigenère Cipher | Text (Keyword) | Low | 1553 | O(n) |
| Affine Cipher | Two numbers (a, b) | Very Low | Ancient | O(n) |
| Atbash Cipher | None | Very Low | ~500 BC | O(n) |
| ROT13 | Fixed (13) | Very Low | Modern | O(n) |
| Playfair Cipher | Text (Keyword) | Low | 1854 | O(n) |