"Preview Talk" (by team Kryptallage) @ TCPT3, in reply to the NIST Threshold Call
Abstract: In this talk we present an overview of our threshold integrated Fully Homomorphic Encryption (FHE) system, Kryptallage, targeting NIST Threshold Categories S4 and S5. Kryptallage unifies several homomorphic encryption schemes and the procedures for switching between them into a single encrypted-computation framework. Rather than working with specific named FHE schemes, we consider ciphertexts through their functionality, message space, encoding, and mathematical representation. This offers a more generic framework to describe scheme switching, via ciphertext characteristics. We will present an overview of the different ciphertext types and how they interact. Our scheme switching approach is used to make leveled evaluation of look-up tables (LUTs), comparisons, and other operations practical at scale. We will motivate and overview the batched circuit bootstrapping process which is used to enable our approach. The FHE specification that we use features distributed key generation and decryption. This is enabled by a module threshold layer that realises these distributed operations using Shamir secret sharing over Galois rings. The threshold protocols are proven UC-secure against a static malicious adversary corrupting t<n/2 parties, providing active security with abort for key generation and guaranteed output delivery for decryption.
Joint work: Ghada Almashaqbeh, Sonia Belaïd, Nicolas Bon, Ilaria Chillotti, Mariana Gama, Antonio Guimarães, Erin Hales, Hyojun Kim, Elena Kirshanova, Damien Ligier, Ryan Orendorff, Emmanuela Orsini, Matthieu Rivain, Luisa Siniscalchi, Ravital Solomon, Rick Weber.
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