Paper 2020/301

MadHatter: A toy cipher that conceals two plaintexts in the same ciphertext

Thomas Kaeding

Abstract

We present a toy cipher that has two novel features: Two plaintexts are concealed by the same ciphertext in different schemes, and the enumeration of the permutations of ciphertext symbols (not the permutations of plaintext symbols, as used in transposition ciphers) forms the basis of one of the schemes. The other scheme uses mixed-radix numbers as substitutes for plaintext symbols. Both schemes use the same symbols, but with different interpretations, and this allows two plaintexts to be encrypted in the same ciphertext.