An Improved RNS Variant of the BFV Homomorphic Encryption Scheme.

We present an optimized variant of the Brakerski/Fan-Vercauteren (BFV) homomorphic encryption scheme and its efficient implementation in PALISADE. Our algorithmic improvements focus on optimizing decryption and homomorphic multiplication in the Residue Number System (RNS), using the Chinese Remainder Theorem (CRT) to represent and manipulate the large coefficients in the ciphertext polynomials. These improvements are based on our original general-purpose techniques for CRT basis extension and scaling that can be applied to many other lattice-based cryptographic primitives. Our variant is simpler and significantly more efficient than the RNS variant proposed by Bajard et al. both in terms of noise growth and the computational complexity of the underlying CRT basis extension and scaling procedures.