Caesar Cipher
Mode
Select encode or decode mode
Shift Amount
Select how many positions to shift (1-25). Current: 3
Alphabet Mapping
Original:
ABCDEFGHIJKLMNOPQRSTUVWXYZ
Shifted by 3:
DEFGHIJKLMNOPQRSTUVWXYZABC
Plain Text
Cipher Text
Related Tools
What is the Caesar Cipher?
The Caesar cipher is one of the oldest and simplest encryption techniques known. Named after Julius Caesar, who used it for his private correspondence, this substitution cipher works by shifting each letter in the plaintext by a fixed number of positions in the alphabet.
For example, with a shift of 3 (Caesar's original choice): A becomes D, B becomes E, C becomes F, and so on. When you reach the end of the alphabet, it wraps around - so X becomes A, Y becomes B, and Z becomes C.
This free online tool lets you encrypt and decrypt text using any shift value from 1 to 25. All processing happens in your browser - your data never leaves your device.
Historical Background
Julius Caesar's Use
According to Roman historian Suetonius, Caesar used a shift of 3 for his military correspondence. The cipher was effective in its time because most enemies couldn't read at all.
Augustus Caesar
Caesar's nephew Augustus also used the cipher, but preferred a shift of 1. This simpler version was easier to use but equally effective against illiterate adversaries.
Medieval Use
The Caesar cipher remained in use throughout the Middle Ages, often employed by religious organizations and governments for routine communications.
Modern Applications
Today, the Caesar cipher is used primarily for puzzles, games, and educational purposes. It forms the foundation for understanding more complex encryption methods.
Frequently Asked Questions
Is the Caesar cipher secure?
No. The Caesar cipher provides no real security. With only 25 possible shifts, it can be broken by trying all possibilities (brute force) or by frequency analysis. Never use it to protect sensitive information.
What's the difference between Caesar cipher and ROT13?
ROT13 is simply a Caesar cipher with a fixed shift of 13. Because 13 is half of 26, ROT13 is symmetric - applying it twice returns the original text. The Caesar cipher allows any shift from 1 to 25.
What happens to numbers and symbols?
The classic Caesar cipher only shifts letters. Numbers, spaces, punctuation, and other characters remain unchanged. This is historically accurate to how Caesar would have used it.
Is my data sent to a server?
No. All encryption and decryption happens entirely in your browser using JavaScript. Your data never leaves your device, making this tool completely private.