Simple Substitution Cipher
SIAA ZQ LKBA
Encode text with a keyword alphabet
A simple substitution cipher replaces every letter with a fixed partner from a scrambled alphabet. The keyword seeds that alphabet — its unique letters come first, then the rest of A–Z in order — so the same keyword always produces the same mapping.
When to use this tool
Reach for the simple substitution cipher when you want a full scrambled alphabet rather than a fixed Caesar shift or Atbash mirror — every letter maps to its own partner. A keyword seeds the mixed alphabet, so it is easy to share and reproduce, making it a classic choice for puzzles, CTF challenges, and classroom demonstrations of how monoalphabetic ciphers work.
Privacy and limitations
Everything runs locally in your browser; nothing is sent anywhere. This is a classical cipher, not real encryption — it only substitutes A–Z and a–z, leaves digits and symbols untouched, and offers no auto-solving. Because each letter always maps to the same partner, the ciphertext is vulnerable to letter-frequency analysis. You need the exact keyword to decode a message.