Laboratoire d'informatique de l'École polytechnique

Talk by Olivier Blazy: «Implicit Proofs of Membership »

Speaker: Olivier Blazy
Location: Online
Date: Thu, 20 Jan 2022, 13:00-14:00

The next LIX Seminar is scheduled this Thursday at 13:00.

We will have the pleasure to listen to Olivier Blazy (Grace team) talking about Implicit Proofs of Membership.

The seminar will be fully online at (full information for connection below).

Abstract: Cryptography is more and more about manipulating secret / encrypted data and managing to do operations associated with their plaintext. One of the major advance in cryptography came from Zero-Knowledge Proofs of Knowledge, that allowed to prove the veracity of a statement without leaking any more information. This technique lead to several major improvements in protocols. However, it leaks the fact that you can indeed prove something.And this could become quite critical, for example : without knowing what’s in your patient file, learning that every week an oncologist accesses it might be an information you want to keep secret. To this end, in this talk, we are going to have a look at Implicit Proofs of Knowledge, and see how they could supersede ZKPK in most modern application for a gain both in privacy and efficiency.

We are going to focus on Smooth Hash Proof Systems, a tool presented by Cramer and Shoup to build compact efficient CCA2 encryption in the standard model. We are going to see, that it could be used to achieve a completely different goal, that is more in line with modern protocols. We will start by a panorama of languages that can be managed by such a primitive and then show how this is enough to instantiate efficiently various protocols. We will provide examples of such constructions first with ‘vanilla’ cryptography (elliptic curve, paillier) but also show that post-quantum constructions can be achieved with a non-prohibitive efficiency in both lattice and code based cryptography, widening the range of primitive available under those hypotheses.

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