Fully Homomorphic Encryption (FHE) permits the evaluation of an arbitrary function on encrypted data. However, FHE ciphertexts, particularly those based on lattice assumptions such as LWE/RLWE are very large compared to the underlying plaintext. Large ciphertexts are hard to communicate over the network and this is an obstacle to the adoption of FHE, particularly for clients with limited bandwidth. In this work, we propose the first technique to compress ciphertexts sent from the server to the client using an additive encryption scheme with smaller ciphertexts. Using the additive scheme, the client sends auxiliary information to the server which is used to compress the ciphertext. Our evaluation shows up to 95% percent and 97% compression for LWE and RLWE ciphertexts, respectively.

翻译：全同态加密（FHE）允许对加密数据上的任意函数进行计算。然而，FHE 密文（特别是基于 LWE/RLWE 等格假设的密文）与底层明文相比体积庞大。大尺寸密文难以通过网络传输，这成为 FHE 应用推广的障碍，尤其对于带宽有限的客户端而言。本文首次提出一种利用密文尺寸更小的加法加密方案来压缩服务器发送至客户端密文的技术。通过该加法方案，客户端向服务器发送辅助信息，用于压缩密文。我们的评估显示，对于 LWE 和 RLWE 密文，压缩率分别可达 95% 和 97%。