Paillier homomorphic encryption outsources ciphertext securely in exchange for cloud computing services at the expense of a huge computation overhead. Therefore, we introduce a 28nm 500MHz 23~68MOPS Paillier Homomorphic Encryption Processor with 0.52~0.18μJ/Op efficiency. It leverages specific arithmetic units to enable basic Paillier operations, provides performance optimization via a reconfigurable design for the processing elements, and develops a PCIe card with 8 chips for scalable computing.