Content for  TS 33.536  Word version:  18.0.0

The link identifier update procedure given in TS 23.287 is used to provide privacy for the identities in the unicast link. This procedure only provides privacy if a non-NULL confidentiality algorithm is selected. This means the messages in this procedure are sent confidentiality protected (i.e. using a non-NULL confidentiality algorithm) and hence the new identities agreed by the UEs are only known to the involved UEs. A three-way message exchange procedure is required with this procedure since both UEs need to change their identifiers during the same procedure and to allow these new values to be acknowledged before them being used. This procedure is used to preserve the privacy for the identities that are seen in the clear for an ongoing unicast connection. A separate privacy threat that allows to link two subsequent connections is caused by either the same KNRP ID or same partial KNRP ID value being sent in the Direct Communication Request message for subsequent connections. The Layer-2 link release procedure given in TS 23.287 is used to provide privacy for the KNRP ID. The messages in the Layer-2 link release procedure are always sent protected and hence the new KNRP ID agreed by the UEs is only known to the involved UEs.