Paper 2024/129

Finite Key OTP Functionality: Ciphers That Hold Off Attackers Smarter Than Their Designers

Abstract

The prevailing ciphers rely on the weak assumption that their attacker is not smarter than expected by their designers. The resultant crypto ecology favors the cryptographic powerhouses, and hinders cyber freedom, cyber privacy and cyber democracy. This weakness can be remedied by using the gold standard of cryptography -- One Time Pad, OTP. Alas, it comes with a prohibitive cost of a key as long as the message it encrypts. When the stakes are high enough users pay this high price because OTP is immunized against smarter and better equipped attackers. Claude Shannon has shown that this size imposition on the key is non-negotiable in the context he analyzed. Alas, changing the context, one could achieve OTP equivalence. Three simple changes are introduced: (i) make the size of the key an integral part of the secret, (ii) every finite message is encrypted with an arbitrary part of the key, (iii) allow for open-ended dilution of the contents-bearing bits of the ciphertext, with content-devoid bits, which don't confuse the intended recipient, but impose an open-ended cryptanalytic barrier before the attacker. A-priori a cryptanalyst is facing a set of messages each of them deemed plausible to be the one hidden in the ciphertext. If the ciphertext is Finite Key OTP compliant then membership in this set will not change after an exhaustive cryptanalytic processing of the ciphertext. This constitutes functional equivalence with OTP. OTP functionality with a shared finite key creates a path to digital freedom, digital privacy and digital democracy.

Note: A detailed account of the various ciphers which are addressed in this article is given in the just published book "Cryptography - Recent Advances and Research Perspectives" 2024, Dr. Sudhakar Radhakrishnan, Editor, in a dedicated chapter: "Pattern Devoid Cryptography".