TSG-Terminals Working Group 3 (USIM) meeting #3	TSGT3#3(99)071
Helsinki 16th - 18th March, 1999	Page 2

Source:	Japan Telecom, NTT DoCoMo, Nippon ERICSSON

Title: Proposed Stage1 Description of Variable Length Security Parameters in 21.11

Agenda Item: 6
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Abstract
This contribution proposes addition of new chapter addrssing "variable length security parameters" to 21.11.

1.	Introductiond

At the last TSG-T3 Munich meting, liaison back from TSG-SA3(t3-99043) was distributed, and noted by the meeting. The liaison said that security parameters have not been decided yet, but provisionally estimated as follows;

•	16 parameters each of maximum length 256 bits
•	All parameters should be accompanied by a length indicator.  This should be 1 byte.

It seems, at least, necessity of variable length security parameters have been commonly recognised in TSG-T3 and TSG-SA3.

2.	Discussion

Regarding this issue, stage1 (requirement) description should be noted in the 21.11. Therefore, we would like to propose to add following new chapter into section 4 (Security Requirements). 

4.4.Variable Length Security Parameters

Security policy may vary operator by operator. However, since 2G standards specifies length of security parameters (i.e. RAND, SRES, Kc) as fixed, operator could not enhance the security level to be applied to his network by the limitation of security parameter length.
Therefore, in order to allow enhancement of security level in accordance with each 3G operator's security policy, length of security parameters should be variable.

 

2.1.	Requirements for this feature

When we consider the functional requirements for this feature, we have to consider cases below. The necessity of capability to achive case 1 and 2 have already agreed. Regarding the case3, since the necessity of this combination is still under study(FFS), this document doesn't address this case. 
Case1) USIM inserted into 3G UE
Case2) GSM SIM inserted into 3G UE
Case3) USIM inserted into GSM ME
In this document, GSM SIM means the SIM only supports traditional authentication algorithm (with fixed length parameters), and USIM means the SIM supports enhanced authentication algorithm with variable length parameters.

2.1.1.	Case1:GSM SIM inserted into 3G UE

This case will be applied when 3G subscriber in home or visited 3G area. Length Indicator should be included in the command to run 3G authentication algorithm (to indicate length of RAND) and it's response (to indicate length of SRES). It is FFS whether existing RUN GSM ALGORITHM command is enhanced or another command (for example RUN 3G ALGORITHN) is newly defined. 

Figure1: Elementary Information Flow for the Case1

2.1.2.	Case2:USIM inserted into 3G UE

This case will be applied when GSM subscriber roams into 3G area with his/her SIM inserting into 3G-UE. Since this case have been agreed as mandatory requirement, 3G UE should support both fixed length parameter set and variable length parameter set. 

Figure2: Elementary Information Flow for the Case2

3.	Proposal

This contribution proposes stage1 description regarding variable length security parameters (see below).
Addition to that, as stated in Tdoc028(Work Proc.), we would like to promote subsequent work (i.e. stage2/3) so that preliminary version (release APR. '99) can support these variable length security parameters. Therefore we will distribute stage2 and 3 proposals ASAP.

4.4.Variable Length Security Parameters

Security policy may vary operator by operator. However, since 2G standards specifies length of security parameters (i.e. RAND, SRES, Kc) as fixed, operator could not enhance the security level to be applied to his network by the limitation of security parameter length.
Therefore, in order to allow enhancement of security level in accordance with each 3G operator's security policy, length of security parameters should be variable.

In order to achieve this feature, following requirement should be covered.

1)	Length Indicator should be included in the command to run 3G authentication algorithm (to indicate length of RAND) and it's response (to indicate length of SRES). 
2)	3G UE should support both fixed length parameter set (for the case of GSM SIM inserted) and variable length parameter set (for the case of USIM inserted).