Network Domain Security (NDS); Authentication Framework (AF)
The scope of this Technical Specification is limited to authentication of network elements, which are using NDS/IP or TLS, and to Certificate Enrolment for Base Stations as described in the present document.
In the case of NDS/IP this specification includes both the authentication of Security Gateways (SEG) at the corresponding Za-interfaces and the authentication between NEs and between NEs and SEGs at the Zb-interface. Authentication of end entities (i.e. NEs and SEGs) in the intra-operator domain is considered an internal issue for operators. This is quite much in line with [1] which states that only Za is mandatory and that the security domain operator can decide if the Zb-interface is deployed or not, as the Zb-interface is optional for implementation. Validity of certificates may be restricted to the operator's domain in case of Zb interface or in case of Za-interface between two security domains of the same operator.
NOTE: In case two SEGs interconnect separate network regions under a single administrative authority (e.g. owned by the same mobile operator) then the Za-interface is not subject to interconnect agreements, but the decision on applying Za-interface is left to operators.
The NDS architecture for IP-based protocols is illustrated in figure 1.
Figure 1: NDS architecture for IP-based protocols [1]
In the case of TLS this Specification concentrates on authentication of TLS entities across inter-operator links. For example, TLS is specified for inter-operator communications between IMS and non-IMS networks TS 33.203 [9] and on the Zn' interface in GBA TS 33.220 [10]. Authentication of TLS entities across intra-operator links is considered an internal issue for operators. However, NDS/AF can easily be adapted to the intra-operator use case since it is just a simplification of the inter-operator case when all TLS NEs and the PKI infrastructure belong to the same operator. Validity of certificates may be restricted to the operator's domain. An Annex contains information on the manual handling of TLS certificates in case automatic enrolment and revocation according to NDS/AF for TLS is not implemented.