Caesar Cipher
Encrypt and decrypt messages the way Julius Caesar did: pick a shift from 1 to 25 (or use the ROT13 preset). Uppercase letters, symbols and spaces are preserved.
A bit of history: from Julius Caesar to ROT13
According to the Roman historian Suetonius, Julius Caesar protected his military correspondence by replacing each letter with the one three positions further down the alphabet: A became D, B became E, and so on. It is one of the oldest documented ciphers. The ROT13 variant, with a shift of 13, has a neat property: since the Latin alphabet has 26 letters, applying it twice brings back the original text — encrypting and decrypting are the exact same operation. That is why it became the standard on 1980s Usenet forums for hiding spoilers and puzzle solutions.
How secure is the Caesar cipher?
Today, not at all: there are only 25 possible shifts, so a brute-force attack tries them all in seconds, and letter-frequency analysis cracks it even by hand — in English, E and T are the most common letters, and they stay the most common in the ciphertext, just shifted. It is still great for games, scavenger hunts, escape rooms, and learning the basics of cryptography: just never use it to protect genuinely sensitive data.