XOR & One-Time Pad
XORs two inputs, text or hex, showing the result in both; a Vernam section enciphers with a key, warning when it is shorter than the message; crib dragging slides a guessed word along two ciphertexts' XOR to expose a reused pad. Gilbert Vernam patented the XOR teleprinter cipher (US 1,310,719, 1919); Shannon (1949) proved a random key as long as the message, used once, gives perfect secrecy.