A Proof System and a Decision Procedure for Equality Logic

Equality Logic with uninterpreted functions is used for proving the equivalense or refinement between systems (hardware verification, compiler translation, etc). Current approaches for deciding this type of formulas use a transformation of an equality formula to the propositional one of larger size, and then any standard SAT checker can be applied. We give an approach for deciding satisfiability of equality logic formulas (E-SAT) in conjunctive normal form. Central in our approach is a single proof rule called ER. For this single rule we prove soundness and completeness. Based on this rule we propose a complete procedure for E-SAT and prove its correctness. Applying our procedure on a variation of the pigeon hole formula yields a polynomial complexity contrary to earlier approaches to E-SA

Secure Key-Updating for Lazy Revocation

We consider the problem of efficient key management and user revocation in cryptographic file systems that allow shared access to files. A performance-efficient solution to user revocation in such systems is lazy revocation, a method that delays the re-encryption of a file until the next write to that file. We formalize the notion of key-updating schemes for lazy revocation, an abstraction to manage cryptographic keys in file systems with lazy revocation, and give a security definition for such schemes. We give two composition methods that combine two secure key-updating schemes into a new secure scheme that permits a larger number of user revocations. We prove the security of two slightly modified existing constructions and propose a novel binary tree construction that is also provable secure in our model