[Resource Topic] 2025/651: Low-Latency Bootstrapping for CKKS using Roots of Unity

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Title:
Low-Latency Bootstrapping for CKKS using Roots of Unity

Authors: Jean-Sébastien Coron, Robin Köstler

Abstract:

We introduce a new bootstrapping equation for the CKKS homomorphic encryption scheme of approximate numbers. The original bootstrapping approach for CKKS consists in homomorphically evaluating a polynomial that approximates the modular reduction modulo q. In contrast, our new bootstrapping equation directly embeds the additive group modulo q into the complex roots of unity, which can be evaluated natively in the CKKS scheme. Due to its reduced multiplicative depth, our new bootstrapping equation achieves a 7x latency improvement for a single slot compared to the original CKKS bootstrapping, though it scales less efficiently when applied to a larger number of slots.

ePrint: https://eprint.iacr.org/2025/651

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