Paper 2023/1223

Improved Circuit Synthesis with Amortized Bootstrapping for FHEW-like Schemes

Johannes Mono, Ruhr University Bochum
Kamil Kluczniak, Helmholtz Center for Information Security
Tim Güneysu, Ruhr University Bochum, German Research Centre for Artificial Intelligence

In recent years, the research community has made great progress in improving techniques for privacy-preserving computation such as fully homomorphic encryption (FHE). Despite the progress, there remain open challenges, mostly in the areas of performance and usability, to further advance the adoption of these technologies. This work provides multiple contributions to improve the current state-of-the-art in both areas. More specifically, we significantly simplify the bootstrapping idea by Carpov, Izabach`ene, and Mollimard [1] for Boolean-based FHE schemes such as FHEW or TFHE, making the concept usable in practice. Based on our simplifications, we provide an easy-to-use interface for amortized bootstrapping implementing our improvements in the open-source library FHE-Deck and provide new parameter sets for multi-bit encryptions with state-of-the-art security. We build a toolset that compiles high-level code such as C++ to code that executes operations on encrypted data. For this toolset, we propose the first non-trivial FHE-specific optimizations in synthesizing privacy-preserving circuits from high-level code, namely look-up table (LUT) grouping and adder substitution. Using LUT grouping, we reduce the number of bootstrapping required by almost 35 % on average, while for adder substitution, we reduce the number of required bootstrapping by up to 80 % for certain use cases. Overall, the execution time is up to 3.8× faster using our optimizations compared to previous state-of-the-art circuit synthesis.

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Publication info
fully homomorphic encryptionFHEWTFHEcircuit synthesis
Contact author(s)
johannes mono @ rub de
kamil kluczniak @ cispa de
tim gueneysu @ rub de
2023-08-15: approved
2023-08-11: received
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      author = {Johannes Mono and Kamil Kluczniak and Tim Güneysu},
      title = {Improved Circuit Synthesis with Amortized Bootstrapping for FHEW-like Schemes},
      howpublished = {Cryptology ePrint Archive, Paper 2023/1223},
      year = {2023},
      note = {\url{}},
      url = {}
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