Patent ID: 7471794

Claim:
A method for determining whether a communication device is permitted to access communication service in a communication network, the communication device comprising: a data memory capable of storing ciphertext access information; and an inerasable memory capable of storing a deciphering key in a non-volatile way; and the method comprising: enciphering access information corresponding to the communication device into the ciphertext access information using a predetermined cryptography algorithm according to an enciphering key stored outside of the communication device, wherein the enciphering key corresponds to the deciphering key, and wherein the communication network comprises a service provider capable of providing communication service to the communication device; there being a database in the service provider for recording the enciphering key corresponding to the communication device; and recording the ciphertext access information in the data memory; reading the deciphering key in the inerasable memory and the ciphertext access information in the data memory; and deciphering the ciphertext access information to plaintext access information according to the deciphering key by using the cryptography algorithm, and determining whether the communication device is permitted to access communication service in the communication network accordingly.