Practice-Oriented Provable Security for Higher-Layer Protocols: Models, Analyses and Solutions

University Of California-Davis, Davis CA

Investigators

Abstract

This research is about using the "provable-security approach" in the design and analysis of high-level cryptographic protocols. The aim is to gain assurance for practical cryptographic schemes by finding the right definitions, and then using modern techniques (reductions and their concrete-security analysis) to analyze selected schemes. Specific problems to be investigated include: (1) Storing a user's private information on an untrusted server. Here one wants to store user data in such a way that the user can recover it by presenting a password, but an adversary must invest an amount of interaction proportional to the guessing-complexity of the password. (2) The authenticated-encryption scheme in SSH. Though the method used by SSH is not, in general, correct, the situation for SSH itself is far from clear. (3) Delegation of authority to a secondary signature key by a primary one. A well-known approach in security practice, the problem that this solution aims to solve is without any provable-security treatment. (4) Relating the "prescriptive" approach to formalizing authenticated key exchange and the simulation-based approach. (5) Moving to an enriched model of computation, an envelope model, to investigate authenticated key exchange. (6) A systematic investigation of the "game walking" approach to analyzing cryptographic scenarios. Here two adversarial views are compared by writing out a sequence of pseudocode "games" each of which may set some Boolean flag. One bounds the difference in adversarial views by bounding the probability that the flag gets set.