Caesar Cipher Encoder and Decoder

About the Caesar Cipher Encoder and Decoder

The Caesar cipher replaces each letter with the letter a fixed number of places further along the alphabet. With a shift of 3, A becomes D, B becomes E and Hello, World! becomes Khoor, Zruog!. Decrypting moves each letter back by the same amount. Letters keep their case, and digits, spaces and punctuation are left alone. ROT13 is the Caesar cipher with a shift of 13. Because the alphabet has 26 letters, applying ROT13 twice returns the original text, so one operation both encrypts and decrypts. The cipher is named after Julius Caesar, who is reported to have used a shift of 3. It offers no real security: there are only 25 useful shifts, so every one can be tried in seconds. The Break it tab does exactly that and ranks the results by how closely their letter frequencies match English, which works well for messages of a few words or more and can be wrong for very short ones. The Vigenere cipher uses a repeating keyword so that each letter gets its own shift: with the key LEMON, ATTACKATDAWN becomes LXFOPVEFRNHR. It is harder to break than a single shift but it is also long obsolete. Use these ciphers for puzzles, teaching and light obfuscation, never to protect anything private.