Classical Cipher Tool
Encrypt or decrypt text with the Caesar, Vigenère, Atbash, and rail-fence ciphers — plus a Caesar brute-force that shows all 26 shifts. Runs entirely in your browser, no server, no sign-up.
What this tool does
Encrypt and decrypt text with four classic pre-computer ciphers — Caesar, Vigenère, Atbash, and rail-fence — entirely in your browser. Nothing is sent to a server: it runs locally, works offline, and needs no sign-up. Pick a Cipher, an Operation, fill in the Key if the cipher needs one, and paste your Text.
These are educational / puzzle ciphers (great for CTFs, escape rooms, and cryptograms). They are not secure encryption — do not use them to protect real secrets.
The ciphers
| Cipher | Key | What it does |
|---|---|---|
| Caesar | shift number (default 3) | Shifts every letter forward by a fixed amount around the alphabet. Shift 3 turns Hello into Khoor. Negative and large shifts wrap (mod 26). |
| Vigenère | a keyword (e.g. LEMON) | Shifts each letter by the next letter of a repeating keyword — a polyalphabetic Caesar. ATTACKATDAWN with key LEMON → LXFOPVEFRNHR. |
| Atbash | none | Mirrors the alphabet: A↔Z, B↔Y, … It is its own inverse, so encrypt and decrypt are the same. Hello → Svool. |
| Rail-fence | number of rails (2–64, default 3) | Writes the text in a zig-zag across N rails, then reads it off rail by rail — a transposition cipher (spaces and punctuation move too). |
In Caesar, Vigenère, and Atbash, case is preserved and digits, spaces, and punctuation pass through unchanged. Rail-fence transposes the whole string, including spaces.
Operations
| Operation | What it does |
|---|---|
| encrypt (default) | Apply the cipher with your key. |
| decrypt | Reverse it with the same key. |
| brute-force | Caesar only. Lists all 26 possible shifts as shift NN: <text> lines so you can spot the one that reads as plain English. |
Examples
| Text | Cipher · Operation · Key | Result |
|---|---|---|
Hello, World! | Caesar · encrypt · 3 | Khoor, Zruog! |
Khoor | Caesar · brute-force | …shift 3: Hello… |
ATTACKATDAWN | Vigenère · encrypt · LEMON | LXFOPVEFRNHR |
Hello | Atbash · encrypt | Svool |
WEAREDISCOVEREDFLEEATONCE | Rail-fence · encrypt · 3 | WECRLTEERDSOEEFEAOCAIVDEN |
FAQ
Is it free and private?
Yes — your text never leaves your device, and it keeps working offline once the page has loaded.
Is ROT13 supported?
Yes — ROT13 is just a Caesar cipher with shift 13. (And
because the alphabet is 26 letters, encrypting and decrypting ROT13 are the same.)
The Vigenère key has spaces or numbers — does that matter?
No. Only the letters of the key are used; spaces, digits, and punctuation in the key are ignored. The key just needs at least one letter.
I have a Caesar message but don't know the shift.
Choose brute-force — it prints all 26 shifts at once so you can read off the one that makes sense.
Are these secure?
No. Classical ciphers are trivially broken with modern tools (and the brute-force here demonstrates exactly that for Caesar). Use them for puzzles and learning, not real security.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool classical-cipher-tool 'cipher=caesar'New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/classical-cipher-tool/?cipher=caesar&operation=encrypt&key=3&text=Attack%20at%20dawnMachine-readable descriptor: tool.json — title + parameters JSON Schema for agents.