Read the messages
you were never meant to.
Decipher is an interactive cryptanalysis workbench. Encrypt, decrypt, and break classical ciphers — from Caesar to DES — with frequency analysis, automatic cipher detection, and a quadgram-scoring solver that cracks substitution ciphers with no key at all.
$ decipher break --auto
ciphertext wkh vshoo lv eurnhq — dqg brx duh iuhh
detected Caesar shift · IoC 0.0663 · χ² minimised at k=3
plaintext the spell is broken — and you are free
Automatic detection
Index of coincidence, χ² and entropy fingerprint the ciphertext and rank the most likely schemes before you lift a finger.
Keyless solvers
Brute-force Caesar and Affine, IoC-driven Vigenère key recovery, and a quadgram hill-climb that reads plain substitution ciphers with no key.
Real block & public-key crypto
A from-scratch DES (ECB/CBC) and educational RSA attacks — modulus factoring and the low-exponent e-th-root — over native BigInt.
Private by construction
Every byte is processed on your device in a Web Worker. No servers, no logging, no network round-trips for your plaintext.
The arsenal
Nine ciphers, one workbench
Each tool encrypts and decrypts, and most come with a dedicated cryptanalytic attack. Pick one, or let auto-detect choose.
Caesar & Atbash
solverThe classic shift cipher and its mirror. Brute-forced across all 26 keys instantly.
open →Affine
solverE(x) = ax + b mod 26. All 312 keys ranked by English fit.
open →Vigenère
solverRepeating-key polyalphabetic. Key length by index of coincidence, key by χ².
open →Monoalphabetic Substitution
solverArbitrary 26-letter mapping, broken keylessly by quadgram hill-climbing.
open →Rail Fence
solverZig-zag transposition. Every rail count tried and scored automatically.
open →Playfair
Digraph cipher on a 5×5 keyed grid. Encrypt and decrypt with any keyword.
open →XOR
solverSingle-byte and repeating-key XOR over raw bytes, with Hamming-distance key recovery.
open →DES
Full FIPS 46-3 DES in ECB and CBC modes, built from scratch over the bit tables.
open →RSA
solverEducational attacks: factor the modulus, or take the e-th root of a low-exponent message.
open →The method
From ciphertext to plaintext in three moves
Paste your ciphertext
Drop in text, hex or Base64. Decipher immediately profiles it and shows the letter-frequency spectrum, index of coincidence and entropy.
Detect or choose
Let the classifier rank likely ciphers from the statistics, or jump straight to the tool you already have in mind.
Break it
Run the attack. Watch the quadgram solver climb toward readable English in real time, or recover a Vigenère key column by column.
Ready to break something?
No sign-up, no upload, no key required for the classics. Open the workbench and start decrypting.
Launch the Workbench →