How to encode and decode classic ciphers
- Choose a cipher and whether you want to encode or decode.
- Set the shift, key, or other setting the cipher uses, and type or paste your text. The result updates as you type.
- Copy the result, or press "Use result as input" to check that it decodes back to the original.
Letters keep their case, and for the letter-based ciphers numbers, spaces, and punctuation are left alone. These ciphers are not secure encryption. For real secrets, use Encrypt & Decrypt Files.
The ciphers
- Caesar
- Moves every letter a fixed number of places along the alphabet. Julius Caesar reportedly used a shift of 3. With only 25 possible shifts it falls to brute force in seconds.
- ROT13
- A Caesar shift of 13. The alphabet has 26 letters, so applying ROT13 twice returns the original. Used online to hide spoilers and punchlines, never for secrecy.
- ROT47
- Like ROT13 but covers the 94 printable ASCII characters from "!" to "~", so digits and punctuation are scrambled too. Applying it twice restores the text.
- Atbash
- Mirrors the alphabet: A becomes Z, B becomes Y, and so on. It has no key, and it was first used with the Hebrew alphabet.
- Vigenère
- Shifts each letter by the matching letter of a repeating keyword (A = 0, B = 1, …). It was called "unbreakable" for centuries, but short keys fall to frequency analysis.
- Affine
- Maps each letter number x to (a × x + b) mod 26. The value a must share no factor with 26 so the process can be reversed. There are only 312 keys.
- Rail fence
- A transposition cipher: the text is written in a zigzag across several rows ("rails") and read off row by row. The letters stay the same, only their order changes.
- Bacon
- Replaces each letter with a group of five A or B symbols (Francis Bacon, 1605), like 5-bit binary. Hidden in a text with two typefaces it becomes steganography.
- A1Z26
- The simplest substitution: A = 1, B = 2, … Z = 26. Letters in a word are joined with hyphens and words are separated by spaces.
- Playfair
- Encrypts pairs of letters using a 5×5 square built from a keyword (I and J share a cell). Used by the British in the First World War. Spaces and punctuation are dropped, and an X pads double letters and odd endings.
Questions
Is my text uploaded anywhere?
No. Every cipher runs in your browser, so your messages and keys never leave your device.
Are these ciphers secure?
No. They are historical ciphers, good for puzzles, geocaching, escape rooms, and learning, and every one of them can be broken quickly. To protect real data, use a modern cipher such as AES-256 with a strong password.
How do I decode a Caesar cipher when I do not know the shift?
Turn on "Try all 25 shifts" while the Caesar cipher is selected. The tool lists the text decoded with every possible shift, and the correct one is the line that reads as normal words.
What is the difference between ROT13 and Caesar?
ROT13 is a Caesar cipher with the shift fixed at 13. Because 13 is half of 26, the same operation encodes and decodes. ROT47 does the same for all printable ASCII characters, so digits and punctuation change too.
Why does Playfair drop my spaces and punctuation?
Playfair works on pairs of letters from a 5×5 square, so only letters are used, I and J share a cell, and an X is inserted between double letters and at an odd end. When you decode, you read the result and remove those extra X characters yourself.
Credits
Built by OneTooling using standard browser features. No third-party code runs on your data.