1. 1 Anonymous Roaming Authentication Protocol with ID-based Signatures Lih-Chyau Wuu Chi-Hsiang Hung Department of Electronic Engineering National Yunlin University of Science & Technology, Taiwan E-mail: wuulc@yuntech.edu.tw

2. 2 Outline  Introduction  Roaming Authentication Protocol  Security Analysis  Performance Analysis  Conclusion

3. 3 Introduction  The mobile communication environment Access data at any place and at any time Security issues  Data privacy  Data integrity  Mutual authentication  Anonymity  Non-repudiation

4. 4 Introduction An authentication server exists in each network Authenticate roaming users before providing any service AS: Authentication Server MS: Mobile Station Home Network Foreign Network AS HN AS FN MS Accept/Reject Roaming Service Request Roaming MS

5. 5 Introduction  Roaming Authentication Methods: On-Line Authentication Off-Line Authentication The mixture of On-Line and Off-Line Authentication

6. 6 On-Line Authentication  Authenticate the roaming user each time Roaming Service Request Is the MS valid? Yes or No Home Network Foreign Network AS HN AS FN MS Accept/Reject Roaming MS

7. 7 Off-Line Authentication  Authenticate the roaming user locally Home NetworkForeign Network Accept/Reject Roaming Service Request pre-shared information AS HN AS FN MS Roaming

8. 8 The mixture of On-Line and Off-Line Authentication On-line authentication when the roaming user requests service for the first time. Off-line authentication for subsequent service requests Home Network Accept/Reject Roaming Service Request Is the MS valid? Yes or No shared information AS HN AS FN MS Roaming Foreign Network

9. 9 The roaming authentication protocol  Off-line roaming authentication  Security properties Anonymity of MS Mutual Authentication between MS and Foreign Network Nonrepudiation of MS  Minimizing the number of exchanged messages  Minimizing the computation load at MS  Simple Key Management

10. 10 The roaming authentication protocol  ID-based signature technique from Weil-pairing No certificate is needed Verify the signature by public information of the signer (email address, identity, …)  Secret sharing technique from Lagrange Interpolating polynomial

11. 11 Lagrange interpolating polynomial - secret sharing ID 1 ID 2 ID n … x 1 =ID 1 and y 1 = f (ID 1 ) x 2 =ID 2 and y 2 = f (ID 2 ) x n =ID n and y n = f (ID n ) y 1 = f (ID 1 ) y 2 = f (ID 2 ) y n = f (ID n )

12. 12 Lagrange interpolating polynomial - secret sharing ID 1 ID 2 ID t … x 1 =ID 1 and y 1 = f (ID 1 ) x 2 =ID 2 and y 2 = f (ID 2 ) x t =ID t and y t = f (ID t ) secret

13. 13 The Roaming Authentication Protocol Home Network Foreign Network K Accept/Reject Sig charge2 AS HN AS FN MS 2 + K MS 1 MS n … RS MS1 RS MS2 RS MSn Roaming Information RS FN

14. 14 System Initialization-AS HN  System Initialization AS HN generates  System public parameters {e, G 1, G 2, P, H 1, H 2, H 3 }  System private key s  System public key P pub = s P AS HN selects a RS FN  R Z q, and sends the RS FN to AS FN by secure channel.

15. 15 System Initialization-AS HN  When MS registers at AS HN, the MS will get {ID MS, TID MS, SK MS, RS MS, K comm } Where PK MS =H 1 (TID MS || ID HN || Date MS ), SK MS = s PK MS Date MS : the expiration date of the public/secret key pair

16. 16 Mutual Authentication  MS roams to the Foreign Network (AS FN ): Foreign Network Compute the Sig charge Compute the session key K Verify the Sig charge Compute the session key K MS AS FN {TID MS, ID HN, Date MS, PK MS, request, T, RS MS, C MS, Sig charge } {E K [ServiceData, T]} or reject

17. 17 Mutual Authentication-MS  MS executes the following steps: Step A1: MS computes the Sig charge ={R charge, S charge } Step A2: MS sends the authentication request to AS FN

18. 18 Mutual Authentication-AS FN  When AS FN receives the request from MS, AS FN will execute the following steps: Step B1: verify the public key PK MS Step B2: check the Date MS then check

19. 19 Mutual Authentication-AS FN Step B3: verify the correctness of Sig charge Step B4: compute the r MS and the session key K Step B5: send to MS

20. 20 Mutual Authentication-MS  When MS receives the message from AS FN, MS computes the session key K’ K’ = K comm ⊕ C MS MS decrypts the by using K’  MS gets the ServiceData and T’ MS checks T’ = T ?

21. 21 Security Analysis  Anonymity of Roaming User  TID MS  Mutual Authentication between MS and AS FN AS FN  MS: Sig charge MS  AS FN : Session key K  Nonrepudiation of Roaming User  Sig charge

22. 22 Security Analysis  Prevention of Attacks Replay Attack  timestamp: T Impersonating Attack MS  Attacker cannot get the SK MS  cannot compute the Sig charge AS FN  Attacker cannot get the RS FN  cannot compute the K Dishonest AS FN  The AS FN cannot compute the Sig charge Disclosure of session key Attacker cannot get the Roaming Share RS FN of AS FN  cannot compute the K

23. 23 Performance analysis [ 7] M. Rahnema, “Overview of the GSM system and protocol architecture,” IEEE Commun. Mag., pp. 92–100, Apr. 1993. [12] J. Zhu, J. Ma, “A new authentication scheme with anonymity for wireless environments,” IEEE Trans. Consumer Electronics, Vol.50, No. 1, pp. 231 – 235, Feb 2004. [ 6] M. Long, C.-H. Wu, J.D. Irwin, “Localized authentication for inter-network roaming across wireless LANs,” IEE Proc. Communications, Vol.151, No5, Oct. 2004. [ 5] W.-B. Lee, C.-K. Yeh, “A New Delegation-Based Authentication Protocol for Use in Portable Communication System”, IEEE Trans. Wireless Communication, Vol.4, No.1, pp. 57-64, Jan. 2005.

24. 24 Performance Analysis  The Number of Exchanged Messages The Number of Exchanged Messages protocolOn-LineOff-Line GSM [7]Mixture62 ZHU[12]Mixture41 Long[6]Off-Line03 Lee[5]Mixture61 OursOff-Line02

25. 25 Performance Analysis  Comparison of Computation Load at MS Asymmetric Computation Symmetric Computation Hash Function GSM [7]On-Line012 Off-Line002 ZHU[12]On-Line022 Off-Line010 M.Long[6]Off-Line310 Lee[5]On-Line111 Off-Line013 OursOff-Line1*10

26. 26 Performance Analysis  Storage Overhead Each MS: {ID MS, TID MS, SK MS, RS MS, K comm } AS FN : RS FN

27. 27 Conclusion  The proposed off-line anonymous roaming authentication Number of exchanged messages: 2 Security Issues Anonymity, Mutual authentication, Non-repudiation, data privacy and data integrity Low computation load at MS Simple key management