A failure in the authentication can occur for several

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A failure in the authentication can occur for several reasons. If the SM1 was not protected, then no protection shall be applied to the failure messages, except the user authentication failure message which shall be protected with the new SAs. If SM1 was protected, the old SAs shall be used to protect the failure messages. In both cases, after processing the failure message, the P-CSCF shall delete the new SAs. The P-CSCF shall monitor the expiry time of registrations without an authentication and if necessary increase the lifetime of SAs created by the last successful authentication such that it will expire shortly after the registration timer in the message. The P-CSCF shall delete any SA whose lifetime is exceeded. The P-CSCF shall delete all SAs it holds that are associated with a particular IMPI once all the associated IMPUs are de-registered. M.7.5 Rules for security association handling when the UE changes IP address The text in clause 7.5 applies without changes. 3GPP 3GPP TS 33.203 V12.67.0 (2014-0609) 73 Release 12
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M.8 ISIM The text in clause 8 applies without changes. M.9 IMC The text in clause 9 applies without changes. 3GPP 3GPP TS 33.203 V12.67.0 (2014-0609) 74 Release 12
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Annex N (normative): Enhancements to the access security to enable SIP Digest N.1 SIP Digest SIP Digest authentication and the requirements in this Annex shall not apply to access networks defined in 3GPP specifications. The P-CSCF can enforce this condition by identifying REGISTER requests relating to SIP Digest according to the rules in Annex P.3 of the present document and discarding them when received over an access network defined in 3GPP specifications. The provisions in Annex N are optional for implementation. The provisions in Annex N are optional for use. However, the use of one of the authentication mechanisms in the present document is mandated. SIP Digest shall not be used in conjunction with IPsec. NOTE 1: The use of SIP Digest in conjunction with IPsec, as specified in the main body and in Annex N of this specification, is technically impossible because SIP Digest does not generate session keys for use with IPsec security associations. An additional scheme for authentication is SIP Digest as specified in RFC 3261 [6]. SIP Digest achieves mutual authentication between the UE and the HN, and is based on HTTP Digest as specified in RFC 2617 [12]. The identity used for authenticating a subscriber is the private identity, IMPI, which has the form of a NAI. The HSS and the UE share a preset secret (e.g., a password) associated with the IMPI. The generation of the authentication challenge shall be done in the same way as specified in RFC 2617 [12] and the present document. It is the policy of the HN that decides if an authentication shall take place for the registration of an additional IMPU that is not part of the already registered set of IMPUs associated with the same IMPI.
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