The cryptographic algorithm is public in modern cryptography. The security of user’s file relies on the protection of the user’s private key. Common practice of protecting private key is to encrypt it with a password and store it in the user’s device. However, the private key is vulnerable to offline dictionary attack when the device is captured by an adversary. In this paper, we analyze the S-RSA protocol and propose an SS-RSA protocol which can resolve the problem of S-RSA that can’t resist the DOS attack and can’t get back the user’s private key after the user cancels the ticket.