Paper 2025/1545

Non-Trivial Ciphertexts

Abstract

A trivial ciphertext is decrypted per all its bits to a corresponding, singular plaintext. A non-trivial ciphertext (NTC) is comprising decryption-proper bits as well as decryption unfitting bits (decoys) with a decryption discrimination key needed to identify each category. A non-trivial ciphertext may also decrypt to different plaintext options, determined by choice of decryption keys. NTC offer important advantages: giving ad-hoc power to buy extra security paid for with an inflated ciphertext, prospectively changing the strategic balance between cryptography and cryptanalysis. NTC involve plaintext alphabet that includes a 'plaintext empty letter' (PEL). Using a particular decryption key, certain ciphertext bits may decrypt to the PEL, and hence have no impact on the decrypted plaintext message constructed from the other bits. Using a different key, different ciphertext bits will decrypt to the PEL while a different collection of the remaining bits will decrypt to a different plaintext message. Thereby one achieves contents discrimination and decryption variety. The number of decoy bits is open-ended and is unilaterally controlled by the transmitter who thus determines the level of projected security -- asymptotically up to Vernam's perfection.

Note: The underlying technology has been inspected by the German Bureau of Standards, TÜV.