Section: 5.1.1 User identity confidentiality
Content: The following security features related to user identity confidentiality are provided: - user identity confidentiality: the property that the permanent user identity (IMSI) of a user to whom a services is delivered cannot be eavesdropped on the radio access link; - user location confidentiality: the property that the presence or the arrival of a user in a certain area cannot be determined by eavesdropping on the radio access link; - user untraceability: the property that an intruder cannot deduce whether different services are delivered to the same user by eavesdropping on the radio access link. To achieve these objectives, the user is normally identified by a temporary identity by which he is known by the visited serving network. To avoid user traceability, which may lead to the compromise of user identity confidentiality, the user should not be identified for a long period by means of the same temporary identity. To achieve these security features, in addition it is required that any signalling or user data that might reveal the user's identity is ciphered on the radio access link. Clause 6.1 describes a mechanism that allows a user to be identified on the radio path by means of a temporary identity by which he is known in the visited serving network. This mechanism should normally be used to identify a user on the radio path in location update requests, service requests, detach requests, connection re-establishment requests, etc.