Operation method and security chip

An operation method applied to a security chip comprising an input/output interface, a decryption circuit, a microprocessor, and an arithmetic unit, the method comprising:

• 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, comprising:
• breaking, by the decryption circuit, the modular exponentiation operation into multiple iterative first operations, wherein 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, wherein the operation parameter comprises a parameter m and a modulus N that is preset to a fixed value, and if the current first operation is an initial first operation, m is a preset initial value, and if the current first operation is not an initial first operation, m is a modular square value or a modular multiplication value obtained after a previous first operation, and
• using, by the decryption circuit, the modular square value or the modular multiplication value obtained after the arithmetic unit performs the first operation for the last time, as an operation result of the modular exponentiation operation;
• and
• using, by the microprocessor, the operation result obtained after the modular exponentiation operation as a plaintext obtained after decryption.