State separation for code-based game-playing proofs

Chris Brzuska*, Antoine Delignat-Lavaud, Cédric Fournet, Konrad Kohbrok, Markulf Kohlweiss

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

2 Citations (Scopus)

Abstract

The security analysis of real-world protocols involves reduction steps that are conceptually simple but still have to account for many protocol complications found in standards and implementations. Taking inspiration from universal composability, abstract cryptography, process algebras, and type-based verification frameworks, we propose a method to simplify large reductions, avoid mistakes in carrying them out, and obtain concise security statements. Our method decomposes monolithic games into collections of stateful packages representing collections of oracles that call one another using well-defined interfaces. Every component scheme yields a pair of a real and an ideal package. In security proofs, we then successively replace each real package with its ideal counterpart, treating the other packages as the reduction. We build this reduction by applying a number of algebraic operations on packages justified by their state separation. Our method handles reductions that emulate the game perfectly, and leaves more complex arguments to existing game-based proof techniques such as the code-based analysis suggested by Bellare and Rogaway. It also facilitates computer-aided proofs, inasmuch as the perfect reductions steps can be automatically discharged by proof assistants. We illustrate our method on two generic composition proofs: a proof of self-composition using a hybrid argument; and the composition of keying and keyed components. For concreteness, we apply them to the KEM-DEM proof of hybrid-encryption by Cramer and Shoup and to the composition of forward-secure game-based key exchange protocols with symmetric-key protocols.

Original languageEnglish
Title of host publicationAdvances in Cryptology – ASIACRYPT 2018 - 24th International Conference on the Theory and Application of Cryptology and Information Security, Proceedings
EditorsThomas Peyrin, Steven Galbraith
Pages222-249
Number of pages28
ISBN (Electronic)9783030033316
DOIs
Publication statusPublished - 1 Jan 2018
MoE publication typeA4 Article in a conference publication
EventInternational Conference on the Theory and Application of Cryptology and Information Security - Brisbane, Australia
Duration: 2 Dec 20186 Dec 2018
Conference number: 24

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume11274 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349

Conference

ConferenceInternational Conference on the Theory and Application of Cryptology and Information Security
Abbreviated titleASIACRYPT
CountryAustralia
CityBrisbane
Period02/12/201806/12/2018

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