The invention provides a device, used in a communication apparatus including a cipher-key generating module, for securing a subscriber's information. The device includes a storage module, a cipher-key acquiring module, an encrypting module and a decrypting module. The subscriber's information is stored in the storage module. The cipher-key acquiring module transmits an input to the cipher-key generating module, and then receives a cipher key generated by the cipher-key generating module in response to the input. The encrypting module retrieves the cipher key through the cipher-key acquiring module, retrieves the subscriber's information from the storage module, and encrypts the subscriber's information using the cipher key to generate an encrypted information. After generated, the encrypted information is stored into the storage module and replaces the subscriber's information. When the subscriber's information needs to be used, the decrypting module retrieves the cipher key through the cipher-key acquiring module, retrieves the encrypted information, and decrypts the encrypted information using the cipher key to recover the subscriber's information. When the decrypting module retrieves the cipher key through the cipher-key acquiring module, the cipher-key acquiring module transmits the input once more to the cipher-key generating module, and then receives the cipher key generated once more by the cipher-key generating module in response to the input.