International Association for Cryptologic Research

International Association
for Cryptologic Research


State Separation for Code-Based Game-Playing Proofs

Chris Brzuska
Antoine Delignat-Lavaud
Cédric Fournet
Konrad Kohbrok
Markulf Kohlweiss
DOI: 10.1007/978-3-030-03332-3_9
Search ePrint
Search Google
Presentation: Slides
Conference: ASIACRYPT 2018
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.
  title={State Separation for Code-Based Game-Playing Proofs},
  booktitle={Advances in Cryptology – ASIACRYPT 2018},
  series={Lecture Notes in Computer Science},
  author={Chris Brzuska and Antoine Delignat-Lavaud and Cédric Fournet and Konrad Kohbrok and Markulf Kohlweiss},