Encrypt, decrypt, and crack classical ciphers interactively
Caesar Cipher — shift each letter by a fixed amount
Vigenere Cipher — polyalphabetic substitution
The Vigenere cipher uses a repeating key to shift each letter differently. Considered unbreakable for centuries until Kasiski (1863) and Friedman's index of coincidence (1922) revealed its structure.
Atbash — reverse the alphabet (A=Z, B=Y...)
Atbash is a simple monoalphabetic substitution cipher where A↔Z, B↔Y, etc. It's self-inverse — encrypting twice gives the original. Used in the Hebrew Bible (e.g., Jeremiah 25:26 encodes "Babel" as "Sheshach").
Monoalphabetic Substitution
Frequency Analysis — crack monoalphabetic ciphers
In English, E (~12.7%), T (~9.1%), A (~8.2%), O (~7.5%), I (~7.0%), N (~6.7%) are most common. By matching cipher frequency to expected English frequency, monoalphabetic ciphers can be cracked.
Mini Enigma — 3 simplified rotors + reflector
The Enigma machine's key property: encryption = decryption (with same settings). Each keypress advances rotor I; rotor I carries to rotor II at position 0. WWII Enigma had 5 rotor choices, 26³ starting positions, plugboard — ~158 quintillion settings.