name: XRES
full_form: Expected User Response
context: AUSF-HN splits the parameter XRES into two equal parts XRES1 and XRES2 (e.g. by choosing XRES1 to be the n least significant bits of XRES where 2n is the length of XRES). The assumption is made here that the knowledge of XRES1 does not help in guessing XRES2. NOTE3: This assumption is believed to be fulfilled when the expected authentication response XRES is pseudo-randomly generated, e.g. as in MILENAGE or TUAK. The AUSF-HN stores XRES temporarily until a protocol timer expires. Editor's Note: The protocol timer is to be defined by CT4. The AUSF-HN then returns an authentication vector AV* in a Response AV message to the SEAF in visited network. The only difference between AV* and an authentication vector AV, as described for EAP-AKAâ in TS 33.402, is that AV* contains only XRES1 while AV contains the full XRES. The AUSF-HN also indicates that EAP-AKA* has been chosen, and it should be terminated in the visited network. The SEAF in visited network understands from the
description: XRES (Expected User Response) is a parameter used in authentication protocols, specifically EAP-AKA', to verify the user's identity. It is generated pseudo-randomly and split into two parts, XRES1 and XRES2, for security purposes.
explanation: The provided context from 3GPP TS 33.899 highlights XRES as a critical parameter in authentication processes, particularly in how it is handled and utilized by the AUSF-HN to generate authentication vectors. This usage aligns with the definition of a Parameter within telecommunications specifications.
section_title: 5.2.4.9.4		Optimization considerations: termination of EAP method in the VPLMN
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