Content for  TS 33.310  Word version:  18.2.0

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8  Backward compatibility for NDS/IP NE's and SEGsp. 40

NDS/IP describes an authentication framework whereby the initial IKEv2 authentication is based on the Pre-shared Secret Key (PSK) authentication method. NDS/AF describes an optional authentication framework which enables NDS/IP end entities (NEs and SEGs) to perform the initial IKEv2 authentication based on signatures. An NDS/AF compliant end entity shall also contain NDS/IP functionality. However, an NDS/IP compliant end entity need not contain NDS/AF functionality unless specifically mandated by TS 33.210 or any other 3GPP specification.
Device-specific management has to be used to reconfigure an end entity such that NDS/AF functionality will be used at the IKE initiator side for the initial IKE authentication (IKEv2 IKE_INIT_SA/IKE_AUTH exchange). The transition towards NDS/AF-based authentication may be done on an end entity by end entity basis. Before the first NDS/AF end entity is taken into use it shall be assured that all needed NDS/AF functionality like CRs, CRL databases are available and working. The setting up of a NDS/AF-based IPsec tunnel can be tested in parallel to the protection of existing traffic using the PSK authentication method.
A smooth migration may be done in the following way:
  • a NDS/AF end entity shall provide several algorithm proposal's during IKE initial authentication, some based on signature authentication, others based on the PSK authentication;
  • the responding IKE peer will select PSK authentication method if it does not support signature authentication methods, but it may select a signature authentication method if it complies with NDS/AF.
  • the IKE responder policy shall be configured such that the signature authentication methods shall take precedence over the PSK authentication method to ensure that it is used as soon as the IKE initiator proposes a signature authentication method.
In case of migration on the Za-interface between two operators:
If the SEGs of both operators support NDS/AF-based authentication then both SEG settings may be changed. The pre-shared secrets may then be removed from the SEGs and the IKE initiator shall only use the RSA signature authentication method. However, this removal of PSK is not essential as it may be used as a fallback mechanism. Some care has to be taken that the policy between SEGs of different operators be coordinated otherwise this may result in failed tunnel set up. This would be the case if the initiating IKE peer only uses the RSA signature authentication method and the responding IKE peer only accepts the PSK authentication method. Furthermore, if the PSK is kept as a fallback mechanism after the RSA signature authentication method is introduced, then fallback to PSK should only be allowed if the operator makes a policy change in the SEGs to allow PSK to be used. The operator may temporarily allow fallback to PSK if, for example, the SEGs are unable to verify the necessary certificates because of problems with the PKI. If PSK is kept as a fallback then it may be necessary to renew the PSK periodically for security reasons, or if PSK compromise is suspected.

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