Caesar Cipher
Encrypt and decrypt text using the Caesar cipher. Shift letters by a configurable amount, or try ROT13.
What is the Caesar Cipher?
The Caesar cipher is one of the oldest known encryption techniques, named after Julius Caesar who reportedly used it to protect military communications. It works by shifting each letter of the alphabet by a fixed number of positions.
For example, with a shift of 3: A becomes D, B becomes E, ..., Z becomes C. To decrypt, shift backwards by the same amount. Despite being trivially easy to break today, it's an excellent introduction to the concept of symmetric encryption.
How to Use
- Choose Encrypt or Decrypt mode
- Set the shift amount (1–25) using the slider or +/− buttons
- Type or paste your text
- Use ROT13 for the classic shift-by-13 cipher
- Use Brute Force to try all 25 shifts when decrypting unknown ciphertext
Frequently Asked Questions
What is ROT13?
ROT13 is a Caesar cipher with a shift of 13. Since 13 + 13 = 26 (the alphabet length), ROT13 is its own inverse — encrypting and decrypting use the same operation.
How secure is the Caesar cipher?
Not at all — for modern use. It has only 25 possible keys and can be broken by frequency analysis or by simply trying all shifts (brute force). Use it only for puzzles, learning, or fun.
Why does the shift wrap around?
The alphabet has 26 letters. A shift of 26 returns every letter to itself. Shifts cycle: shift 27 is the same as shift 1. This is modular arithmetic.
How do I decrypt without knowing the shift?
Use the Brute Force feature to see all 25 possible decryptions. The one that forms readable text is the correct one.
What is the difference between Caesar cipher and ROT13?
ROT13 is simply a Caesar cipher with a fixed shift of 13. Caesar cipher allows any shift value from 1 to 25.