Method for dynamically updating cellular phone unique encryption keys

In a method for dynamically updating a cellular-phone-unique-encryption key previously stored in, and common to, each of a cellular phone and an associated home location register (HLR) for providing security in a cellular-phone-network operation, a random number and shared secret random data generated at least partly based on the random number are transmitted and verified between the cellular phone and the associated HLR. A previously stored version of the cellular-phone-unique-encryption key is then dynamically updated in both the cellular phone and in the HLR by independent calculations based on an algorithm using the shared secret random data and the previously stored version of the cellular-phone-unique-encryption key. In this manner, the cellular-phone-unique-encryption key is dynamically updated as desired, e.g., each time a user initiates a call, and the latest version of the cellular-phone-unique-encryption key independently calculated by the cellular phone and the HLR is not transmitted during the updating process, thereby substantially eliminating the possibility of the latest version of the cellular-phone-unique-encryption key being intercepted during transmission by unauthorized parties.