1. An Authentication Scheme for Mobil Satellite Communication Systems Advisor: Prof. Jen-Chang Liu Graduate Student: Yi-Ching Chen( 陳怡靜 92321527) Date: 2004/05/26 M. S. Hwang, C. C. Yang, and C. Y. Shiu, ACM SIGOPS Operating Systems Review, Vol. 37, No. 4, pp. 42-47, October 2003

2. 2An Authentication Scheme for Mobil Satellite Communication Systems Points in this paper Discussing the security aspects of a registration protocol in a mobile satellite communication system Proposing a new mobile user authentication and data encryption scheme for mobile satellite communication systems The scheme can remedy a replay attack

3. 3An Authentication Scheme for Mobil Satellite Communication Systems Online Introduction of Satellite Communication Systems LEO (Mobile) Satellite Communication System A New Authentication Scheme for MSCS Security Analysis and Conclusion

4. Introduction of Satellite Communication Systems

5. 5An Authentication Scheme for Mobil Satellite Communication Systems MSCS Mobile Satellite Communication System (MSCS) Mobile Communication System –L–Large broadcasting range –L–Large communication area Satellite Communication System –N–No geographic or environmental limitations –C–Communicate around the globe MSCS is the best communications system for out of the way terrain or tall mountain ranges.

6. 6An Authentication Scheme for Mobil Satellite Communication Systems GEO & LEO of MSCS Geostationary Earth Orbit (GEO) –T–The traditional satellite communication system –T–The GEO distance is far from the earth, therefore, there is a signal communication delay problem. –G–GEO is not fit for use in a Personal Communication System (PCS) Low Earth Orbit (LEO) satellite communication systems –U–Using 26 LEO satellite to constitute exact global MSCS –L–LEO satellite orbits closer to the earth than the GEO satellite –L–LEO satellites are fit for use in PCS

7. 7An Authentication Scheme for Mobil Satellite Communication Systems LEO of MSCS Three main advantages in LEO satellite systems –T–The signal communication attenuation is small –T–The signal communication delay time is short –T–The data communication channels are wide but narrower than GEO The disadvantages in LEO satellite systems –B–Being not provided powerful computation

8. 8An Authentication Scheme for Mobil Satellite Communication Systems An past protocol in 1996 Cruickshank, in 1996, proposed an authentication protocol for satellite networks. –U–Using a public-key cryptosystem for mutual authentication between the mobile user and satellite network –U–Using a secret key to encrypt confidential data This protocol can satisfy two security requirements. Disadvantage: This protocol need to spend high computation for LEO satellite systems. Hwang, Yang, Shiu propose an efficient authentication protocol for LEO satellite systems. Two security requirements: 1. An eavesdropper can’t intercept massages during the communication. 2. The service isn’t obtained fraudulently in order to avoid usage charge.

9. LEO (Mobile) Satellite Communication System

10. 10An Authentication Scheme for Mobil Satellite Communication Systems LEO (Mobile) Satellite Com. System The LEO satellite Communication system is comprised of –LEO satellites –A gateway –Mobile users –A Network Control Center (NCC) The LEO satellite orbit is near the earth –The communication signal delay time is short –The signal weakness is slight –The LEO communication range is smaller –The LEO orbit time is short The mobile users and satellites have a hand-over problem

11. 11An Authentication Scheme for Mobil Satellite Communication Systems LEO (Mobile) Satellite Com. System NCC Gateway Mobile User LEO Satellite

12. A New Authentication Scheme for MSCS

13. 13An Authentication Scheme for Mobil Satellite Communication Systems New Scheme Using a session key to encrypt confidential data Two phases in new scheme –Mobile user registration –Mobile user authentication Mobile user registration –Gateway allocates the new mobile user a permanent identity (U ID ), secret key (K md ), and a temporary identity (T ID ) –K md : a secret key shared by the mobile user and the NCC –LEO ID : identity ID of LEO Mobile user’s ID NCC stores these messages (U ID, T ID, K md ) and LEO ID for each mobile user Mobile user stores a message (U ID, T ID, K md ) in private NCCGateway

14. 14An Authentication Scheme for Mobil Satellite Communication Systems New Scheme Mobile user authentication –AUTH Request –U ID 、 T ID 、 K md 、 K md (  ) S1 S2 S3 S4 S5 MSLEONCC AUTH Request T ID, K md (U ID, T ID ) T ID, K md (T ID, T ’ I D, K ’ md ) T ID, K md (U ID, T ID ), LEO ID T ID, K md (T ID, T ’ I D, K ’ md ), LEO ID

15. Security Analysis & Conclusion

16. 16An Authentication Scheme for Mobil Satellite Communication Systems Security Analysis & Conclusion Security Analysis –The mobile user’ location is protected. –An attacker can’t use the old T ID to impersonate the mobile user. –This scheme avoid the replay attack. –LEO can’t decrypt and obtain the transmitted messages. Conclusion –Proposing a simple authentication scheme for MSCS –By using a symmetric cryptosystem –This scheme reduces the computation and enhances the security