CKKS – Addition and Multiplication

Table of Contents This is part of a tutorial series on the CKKS homomorphic encryption scheme. In the last article, we introduced symmetric and public-key encryption and decryption routines, and implemented modular polynomial arithmetic (using NTTs as a black box). This article covers the addition and multiplication operations performed on ciphertexts (without relinearization). Again, if you already know about CKKS, we are still avoiding the RNS form of the scheme and using a 64-bit modulus $Q$, which means that we’re momentarily ignoring cryptographic security.