Paillier is a commonly used semi-homomorphic encryption algorithm that satisfies additive homomorphism. The key generation process is as follows:
The data encryption and decryption and homomorphic algorithms are as follows:
Regarding the Paillier decryption algorithm, CRT (Chinese Remainder Theorem) can be used to improve the performance of the algorithm, see the reference for details: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1 .1.112.4035&rep=rep1&type=pdf