TSG-SA WG3 (Security) meeting #7		S3-99387
The Hague, The Netherlands, 26—27 October 1999

Agenda Item:	10.2

Source:	Siemens Atea

Title:	The 3GPP AKA as an ESA candidate

Document for:	Discussion and decision

1	Introduction
The 3GPP AKA is proposed by 3GPP for Enhanced Subscriber Authentication (ESA) in TIA/EIA. 
The main trumps of the mechanism– when compared to the other symmetric key mechanism (LESA) – are the simplicity of the mechanism and the fact that if adopted by TIA/EIA, a single security architecture is available, what would facilitate global roaming as well as a global market. 
Its drawbacks – compared to LESA as a candidate for ESA – are that it represents a larger deviation from the current IS-41 procedures and that in its own the 3GPP AKA does not meet some of the requirements on network capabilities that are listed in their Stage 1 desciption (see S3-99376):
1)	“The Home system can share authentication key data with visited systems to enable the visited system to perform authentication procedures, thereby minimizing network signalling traffic.”
2)	“Broadcast (global) challenges can be used for pre-call authentication of service requests on control channels.”
The other requirements are met by the 3GPP AKA, especially
3)	“Individual challenges of an MS can be used on dedicated (bearer or signalling traffic) channels.” 
Because of these drawbacks, it is likely that the TR-45.2 subcommittee (and possibly also others) will not select the unmodified 3GPP AKA. 
We therefore propose that the proposal is modified and that the 3GPP S3 makes the necessary changes to 3G TS 33.102 to accommodate for the new proposal.
2	The modified proposal
1)	In both systems the 3GPP AKA mechanism (using quintets) is used to establish shared secret data of twice 128 bits between the user and the serving network. 
2)	In 3GPP SNs the shared secret data shall be used as a cipher/integrity key set as it is currently specified in 3G TS 33.102. 
3)	In 3GPP2 SNs the shared secret data 
a)	shall or may be used as SSD-A and SSD-B to derive session keys as in the lower-tier of the LESA proposal.
TIA/EIA may also decide to allow that the shared secret data 
b)	may (alternatively) be used as a cipher/integrity key set as it is currently specified in 3G TS 33.102. 
3	Evaluation
This new proposal is believed to meet the TR-45.2 requirements: it provides authentication key data by means of the 3GPP AKA, which may subsequently be used by the lower-tier of LESA to derive session keys. It is the lower-tier LESA mechanism that allows for authentication of service requests on the common control channels when the user is already registered. 
This new proposal also provides a global market for AuC and a single interface for authentication between the SN and the HE, that consist of the authentication data request/response proedure desribed in 3G TS 33.102.
As a result the new proposal provides global roaming without the need for gateway functionality or protocol translation.