# Game-based cryptography in HOL

 Title: Game-based cryptography in HOL Authors: Andreas Lochbihler, S. Reza Sefidgar and Bhargav Bhatt (bhargav /dot/ bhatt /at/ inf /dot/ ethz /dot/ ch) Submission date: 2017-05-05 Abstract: In this AFP entry, we show how to specify game-based cryptographic security notions and formally prove secure several cryptographic constructions from the literature using the CryptHOL framework. Among others, we formalise the notions of a random oracle, a pseudo-random function, an unpredictable function, and of encryption schemes that are indistinguishable under chosen plaintext and/or ciphertext attacks. We prove the random-permutation/random-function switching lemma, security of the Elgamal and hashed Elgamal public-key encryption scheme and correctness and security of several constructions with pseudo-random functions. Our proofs follow the game-hopping style advocated by Shoup and Bellare and Rogaway, from which most of the examples have been taken. We generalise some of their results such that they can be reused in other proofs. Thanks to CryptHOL's integration with Isabelle's parametricity infrastructure, many simple hops are easily justified using the theory of representation independence. Change history: [2018-09-28]: added the CryptHOL tutorial for game-based cryptography (revision 489a395764ae) BibTeX: @article{Game_Based_Crypto-AFP, author = {Andreas Lochbihler and S. Reza Sefidgar and Bhargav Bhatt}, title = {Game-based cryptography in HOL}, journal = {Archive of Formal Proofs}, month = may, year = 2017, note = {\url{https://isa-afp.org/entries/Game_Based_Crypto.html}, Formal proof development}, ISSN = {2150-914x}, } License: BSD License Depends on: CryptHOL Used by: Constructive_Cryptography_CM, Multi_Party_Computation