3GPP TSG SA WG3 (Security) meeting #8	Tdoc S3-99459
Sophia Antipolis, 16-19 November, 1999

			
	
3G CHANGE REQUEST	Please see embedded help file at the bottom of this
page for instructions on how to fill in this form correctly.	
	
	33.102	CR	022r1	Current Version:	3.2.0		
					
3G specification number 		 CR number as allocated by 3G support team	
	
For submision to TSG	SA#6	for approval	X	(only one box should	
list TSG meeting no. here 	for information		be marked with an X)	
	
Form: 3G CR cover sheet, version 1.0        The latest version of this form is available from: ftp://ftp.3gpp.org/Information/3GCRF-xx.rtf	
	
Proposed change affects:	USIM	X	ME	X	UTRAN	X	Core Network	X	
(at least one should be marked with an X)	
	
Source:	TSG SA WG3	Date: 	1999-11-18	
	
Subject:	Refinement of Enhanced User Identity Confidentiality	
	
3G Work item:	Enhanced User Identity Confidentiality	
	
Category: 	F	Correction					
	A	Corresponds to a correction in a 2G specification					
(only one category 	B	Addition of feature					
shall be marked	C	Functional modification of feature	X				
with an X)	D	Editorial modification					
	
Reason for 
change:
	Refinement and clarification of enhanced user identity confidentiality mechanism

Clauses affected:	6.2; Annex B	
Other 3G core specifications	
Other 2G core specifications		X	  List of CRs:	33.103CR001r1	
affected:			  List of CRs:		
	MS test specifications		  List of CRs:		
	BSS test specifications		  List of CRs:		
	O&M specifications		  List of CRs:		
	
Other 
comments:		

  <--------- double-click here for help and instructions on how to create a CR.

6.2	Identification by a permanent identity
The mechanism described in here allows the identification of a user on the radio path by means of the permanent user identity (IMUI). 
The mechanism should be invoked by the serving network whenever the user cannot be identified by means of a temporary identity. In particular, it should be used when the user registers for the first time in a serving network, or when the serving network cannot retrieve the IMUI from the TMUI by which the user identifies itself on the radio path. 
The mechanism is illustrated in Figure 3.

Figure 3: Identification by  the permanent identity
The mechanism is initiated by the visited SN/VLR that requests the user to send its permanent identity. According to the user’s preferences, his response may contain either 1) the IMUI in cleartext, or 2) the user’s HE-identity in cleartext and an HE-message that contains an encrypted IMUI. 
The term HE-id denotes an expression which is sufficient to route the User identity request message to an appropriate network element of the HE. Annex B contains a proposal to use MCC, MNC and the first three digits of the user’s MSIN as routing information to address an HE/HLR.
In case the response contains the IMUI in cleartext, the procedure is ended successfully. This variant represents a breach in the provision of user identity confidentiality.
In case the response contains an encrypted IMUI, the visited SN/VLR forwards the HE message to the user’s HE in a request to send the user’s IMUI. The user’s HE then derives the IMUI from the HE-message and sends the IMUI back to the SN/VLR. Annex B describes an example mechanism that makes use of group keys to encrypt the IMUI.
Annex B (Informative): Enhanced user identity confidentiality
This mechanism allows the identification of a user on the radio access by means of  the permanent user identity encrypted by means of a group key. The mechanism described here can be used in combination with the mechanism described in 6.2 to provide user identity confidentiality in the event that the user not known by means of a temporary identity in the serving network. 
The mechanism assumes that the user belongs to a user group with group identity GI. Associated to the user group is a secret group key GKGI which is shared between all members of the user group and the user’s HE/HLR, and securely stored in the USIM and in the HE/HLR. 
The mechanism is illustrated in Figure B.1. 

Figure B.1: Identification by means of the IMUI encrypted by means of a group key
The user identity procedure is initiated by the visited SN/VLR. The visited SN/VLR requests the user to send its permanent user identity. 
Upon receipt the user increments SQNUIC as a time variant parameter TVP. The user encrypts SQNUIC and the IMUI with enciphering algorithm f6 and his group key GKGI. The SQNUIC prevents traceability attacks. The user sends a response to the SN/VLR that includes MCC||MNC||HLR-id and the first three digits of the user’s MSIN and identifies an HLR within the core network.
Note: Alternatives are:
•	to define a single network element within each HE which performs all decryption related to EMUI or
•	that all gateways ;MSCs are able to decrypt EMUI and route the message to the correct HLR.
Upon receipt of that response the SN/VLR should resolve the user’s HE/HLR address from MCC||MNC||HLR-id and forwards the group identity GI and the user’s EMUI to the user’s HE/HLR.
Upon receipt the HE/HLR retrieves the group key GKGI associated with the group identity GI. The HE/HLR then decrypts EMUI with the deciphering algorithm f7 (f7 = f6-1) and the group key GK and retrieves SQNUIC and IMUI. SQNUIC is no longer used. The HE/HLR sends the IMUI in a response to the visited SN/VLR.