Embodiments of the present application disclose an operation method. The method includes: obtaining, by the input/output interface, an input ciphertext; performing, by the decryption circuit, a modular exponentiation operation according to the ciphertext and a preset operation parameter; and using, by the microprocessor, an operation result obtained after the modular exponentiation operation as a plaintext obtained after decryption. The performing, by the decryption circuit, a modular exponentiation operation according to the ciphertext and a preset operation parameter is specifically: breaking, by the decryption circuit, the modular exponentiation operation into multiple iterative first operations, where the first operation is a modular square operation or a modular multiplication operation; sending, by the decryption circuit, the ciphertext and the operation parameter to the arithmetic unit; and performing, by the arithmetic unit, the first operation according to the ciphertext and the operation parameter to obtain a modular square value or a modular multiplication value.