How to copyright a function?

Abstract

This paper introduces a method for tracking different copies of functionally equivalent algorithms containing identification marks known to the attacker. Unlike all previous solutions, the new technique does not rely on any marking assumption and leads to a situation where each copy is either traceable or so severely damaged that it becomes impossible to store in polynomial space or run in polynomial time. Although RSA-related, the construction is particularly applicable to confidential block-ciphers such as SkipJack, RC4, GOST 28147-89, GSM A5, COMP128, TIA CAVE or other proprietary executables distributed to potentially distrusted users.