Cryptography Playground
Type plaintext, watch ciphertext update live. Four classic ciphers, frequency analysis for both plain and cipher text, and a crack mode where you break an encrypted message with only the ciphertext.
Caesar cipher
The oldest known cipher. Each letter is shifted by a fixed number of positions in the alphabet. With only 25 possible keys, it falls to brute force in seconds. Julius Caesar used a shift of 3.
Vigenère cipher
A polyalphabetic cipher using a keyword. Each letter of the key determines the shift for the corresponding letter of plaintext. For centuries it was called "le chiffre indéchiffrable" — until Babbage and Kasiski cracked it by finding repeated patterns.
Substitution cipher
Every letter maps to a different letter via a random permutation. 26! possible keys (about 4 × 10²&sup6;) make brute force impossible, but frequency analysis — invented by Al-Kindi in 9th-century Baghdad — defeats it easily.
Rail fence cipher
A transposition cipher. The plaintext is written in a zigzag across a number of "rails," then read off row by row. The letters are the same — only their order changes. Frequency analysis is useless here; pattern analysis is needed instead.