Cryptology ePrint Archive: Report 2017/430
Improving TFHE: faster packed homomorphic operations and efficient circuit bootstrapping
Ilaria Chillotti and Nicolas Gama and Mariya Georgieva and Malika Izabachène
Abstract: 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.
Category / Keywords: public-key cryptography / FHE, leveled, bootstrapping, LWE, GSW, packing, weighted automata, arithmetic
Date: received 18 May 2017
Contact author: ilaria chillotti at uvsq fr
Available format(s): PDF | BibTeX Citation
Version: 20170522:213506 (All versions of this report)
Short URL: ia.cr/2017/430
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