The present invention relates to a method and network equipment for implementing a security mechanism for interworking with an independent SEAF (security anchor function) in a 5G network. The method performed by the independent SEAF is the step of receiving a first request for a key for securing communication between the UE 12 and a first access and mobility function (AMF) requesting registration by the UE, wherein the request is Including a first indication indicating whether the independent SEAF is supported; Receiving a second request for a key for securing communication between the UE and the second AMF from the second AMF for which the UE requests registration in order to perform mobility between AMFs for the 2 AMF, the request supporting the independent SEAF of the UE Including a second indication indicating whether or not; And determining whether a bid down attack has occurred depending at least in part on whether the first indication matches the second indication.
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