Security Tools | Green Roots

Caesar Cipher

One of the oldest encryption techniques - shift every letter by a fixed number to encode or decode a message.

Mode

Encode Decode

Shift amount: 3

A shift of 3 is the classic ROT-3 used by Julius Caesar himself.

Your message

Numbers, spaces, and punctuation are kept unchanged. Only A-Z letters are shifted.

Result

How it works

The Caesar cipher is a substitution cipher - one of the earliest known encryption methods, used by Julius Caesar to send secret military messages around 58 BC.

Each letter in the plaintext is replaced by the letter a fixed number of positions later in the alphabet. With a shift of 3:

A → D   B → E   C → F   …
X → A   Y → B   Z → C

So "HELLO" becomes "KHOOR" with a shift of 3.

Why is it insecure today?

There are only 25 possible shifts, so an attacker can try all of them in seconds - this is called a brute-force attack. Modern encryption (like AES-256) uses keys so large that brute-forcing them would take longer than the age of the universe.

Key terms

Plaintext - the original readable message
Ciphertext - the encoded message
Key - the shift value (the secret both parties share)
Brute force - trying every possible key until one works