The present application discloses an RSA decryption processor and a method for controlling an RSA decryption processor. A specific implementation of the processor includes a memory, a control component, and a parallel processor. The memory is configured to store decryption parameters comprising a private key. The control component is configured to receive a ciphertext set, and send a decryption signal comprising the ciphertext set to the parallel processor. The parallel processor is configured to: read a decryption parameter from the memory in response to receiving the decryption signal, and use at least one modular exponentiation circuit unit in the parallel processor to perform in parallel a modular exponentiation operation on ciphertexts in the ciphertext set by using the read decryption parameter, to obtain plaintexts corresponding to the ciphertexts. This implementation improves the efficiency of RSA decryption.