1. Improving TFHE: faster packed homomorphicoperations and efficient circuit bootstrapping 2017 Asiacrypt FHE
    Ilaria Chillotti and Nicolas Gama and Mariya Georgieva and Malika Izabachène
    [View PDF on eprint.iacr.org]
    [Show BibTex Citation]

    @misc{cryptoeprint:2017:430,
    author = {Ilaria Chillotti and Nicolas Gama and Mariya Georgieva and Malika Izabachène},
    title = {Improving TFHE: faster packed homomorphic operations and efficient circuit bootstrapping},
    howpublished = {Cryptology ePrint Archive, Report 2017/430},
    year = {2017},
    note = {\url{https://eprint.iacr.org/2017/430}},
    }

In this paper, we present several methods to improve the evaluation of homomorphic functions, both for fully and for leveled homomorphic encryption. We propose two packing methods, in order to decrease the expansion factor and optimize the evaluation of look-up tables and random functions in TRGSW-based homomorphic schemes. We also extend the automata logic, introduced in [19, 12], to the efficient leveled evaluation of weighted automata, and present a new homomorphic counter called TBSR, that supports all the elementary operations that occur in a multiplication. These improvements speed-up the evaluation of most arithmetic functions in a packed leveled mode, with a noise overhead that remains additive. We finally present a new circuit bootstrapping that converts TLWE into low-noise TRGSW ciphertexts in just 137ms, which makes the leveled mode of TFHE composable, and which is fast enough to speed-up arithmetic functions, compared to the gate-by-gate bootstrapping given in [12]. Finally, we propose concrete parameter sets and timing comparison for all our constructions.

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