What is the Caesar Cipher?
The Caesar cipher is one of the oldest and simplest encryption methods, attributed to Julius Caesar who used a shift of 3. Each letter is shifted a fixed number of positions in the alphabet. A→D, B→E, C→F with shift 3. To decode, shift in the opposite direction.
ROT13 — The Most Popular Caesar Variant
ROT13 (rotate by 13) is a special case where encoding and decoding are the same operation — because 13 is exactly half of 26. Apply ROT13 twice to get back the original text. It was widely used on Usenet and early internet forums to hide spoilers.
Security Note
The Caesar cipher is NOT secure for any real purpose. With only 25 possible shifts, brute force takes seconds. Modern cryptography uses algorithms like AES. Use Caesar only for puzzles, games, and education.
How do I decode a Caesar cipher without knowing the shift?
Use the Brute Force option above — it shows all 25 possible decryptions. Readable text will be immediately obvious.
Is ROT13 the same as Caesar cipher shift 13?
Yes. ROT13 is simply a Caesar cipher with a shift value of 13. The special property of ROT13 is that applying it twice returns the original text.