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FHE Beyond IND-CCA1 Security

by Jérôme Nguyen - 2024.07.11

Video recording (Youtube) | Join the discussion (Discord)

Abstract

It is standard to consider a fully homomorphic encryption (FHE) scheme secure if it maintains the privacy of the encrypted messages under chosen-plaintext attacks (CPA). However, in the past few years more and more practical attacks on various CPA-secure FHE schemes have shown that this is too optimistic. This talk will give an overview of the different attack vectors that are not covered by CPA security. We then will discuss a new notion of security for FHE schemes: indistinguishability against verified chosen-ciphertext attacks (vCCA). We will see how the vCCA notion breaks some previous theoretical bounds and how it provides a better security model for FHE schemes to aim for. Finally, we will show how this new level of security can be achieved from popular FHE schemes such as BGV or TFHE.

About the speaker

Jérôme is a PhD student at the Universität der Bundeswehr in Munich. His research focuses on fully homomorphic encryption, as well as lattice-based cryptography in general. He is also broadly interested in all themes of cryptography ranging from theoretical foundations to multi-party computations.

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