Authors: Kui Ren, Wenjing Lou, Kwangjo Kim, and Robert Deng

A Novel Privacy Preserving Authentication and Access Control Scheme for Pervasive Computing Environments Authors:Kui Ren, Wenjing Lou, Kwangjo Kim, and Robert Deng Sources: IEEE Transactions on Vehicular Technology, 55(4), pp. 1373-1384, July 2006. Reporter: Chun-Ta Li (李俊達)

Outline • Pervasive computing environments (PCE) • Motivations • The proposed scheme • Analysis • Comments 2 2

Pervasive computing environments • Definition • Integrates digital devices (such as computers, handheld devices, sensors and actuators) seamlessly with everyday physical devices (such as electrical appliances and automobiles). • Three components [James Kurose and Keith Ross, 2004] • Nomadic computing: wireless-technology • Sensor-based smart spaces: environment-monitoring • Mobile computing data management • Sensor network

Pervasive computing environments • Service-Oriented Architecture

Pervasive computing environments • Sample PCE Public Internet Router Authentication Server Authentication Server Access Point Access Point Fax Gateway User Scientific Device Printer Scanner

Motivations • Providing explicit mutual authentication between mobile user and the service • Allowing mobile user to anonymously interact with the service • Enabling differentiated service access control among different users • Providing flexibility and scalability to both user and service sides • Generating fresh session keys to secure the interaction • Efficiency of communication, computation and management overheads

The proposed scheme • Notations

Authentication Server Service Access Point Mobile User The proposed scheme (cont.) • System architecture 1. Registration 4. Authentication Request 5. Authentication Acknowledgement 2. Authorization 3. Access Request 6. Access/Reject

The proposed scheme (cont.) • User authorization protocol • Credential generation Mobile user U(a certificate CertU) Service provider S 1. Generate two nonces: r’U and r”U 2. Sign her own ID with a nonce r”U  {U, r”U}PriKU 3. Compute the anchor value C0 h(r”U, U, {U, r”U}PriKU) Non-repudiation property 4. Compute the credential chain Cn hn(C0), with length n 5. Blind Cn as CU {r’U}PubKSID * Cn

The proposed scheme (cont.) • User authorization protocol • Credential authorization Mobile user U(a certificate CertU) Service provider S U, CU, CertU, SID authorization request 6. Verify CertU with PubKS 7. Sign CU as CS {CU}PriKSID = r’U * {Cn}PriKSID CS authorization confirmation 8. Compute CS/r’U (Cn, {Cn}PriKSID)

The proposed scheme (cont.) • User operational protocol Mobile user U Service provider S Access point P 1. Generate a nonce: rU 3. Send {rU, Cn, {Cn}PriKSID}PubKS 2. Send {rU, Cn, {Cn}PriKSID}PubKS access request access request secure tunnel 4. Decrypt rU, Cn 5. Store Cn 6. Send rU, Cn access acknowledgement secure tunnel 7. Generate a nonce: rP 8. Compute KUP=h(Cn, rP, rU, 0). K’UP=h(Cn, rP, rU, 1) 9. Send rP, {rU, P}KUP access acknowledgement

The proposed scheme (cont.) • User operational protocol Mobile user U Service provider S Access point P 10. Compute KUP=h(Cn, rP, rU, 0), K’UP = h(Cn, rP, rU, 1). 11. Decrypt and verifies rU, Cn, P 12. Encrypt Xm0 = {m0}K’UP 13. Compute hKUP(Xm0) 14. Send rP, rU, Xm0, hKUP(Xm0) authenticated data traffic 15. Verify Xm0using KUP 16. Decrypt m0using K’UP … … … … rP, rU, Xmi, hKUP(Xmi) authenticated data traffic

Analysis

Comments • Cryptanalysis of anonymity property Service provider S Step 1: Get U, CU = {r’U}PubKSID * Cn in Credential Authorization phase Step 2: Sign CU as CS {CU}PriKSID = r’U * {Cn}PriKSID Step 3: Store U, CU, CS= {CU}PriKSID = r’U * {Cn}PriKSID in their own DB Step 4: Get Cn, {Cn}PriKSID in User Operational phase Step 5: Compute CS / {Cn}PriKSID to derive r’U Step 6: Compute C’U = {r’U}PubKSID * Cnto verify whether C’U = CU holds or not. Step 7: If it holds, S confirms that mobile user U accesses the service; otherwise, S continuallyexecutes the previous Steps from 4 to 6.

Comments (cont.) • Efficiency improvement in user operational phase • compared Cj with all Cjs stored in S’s DB • Time complexity is O(n) if there are n users in DB • solution: Useri generates a TID in access request message and sends it to service provider to store the TID of useri • Time complexity is O(1)

Comments (cont.) • Service abuse problem • No one can derive the value of Cn unless user itself and thus anyone can fabricate an invalid Cn with a valid CertU to access the service without limits even than a valid user can deny his accesses. • CertU must keep secret for outsiders Mobile user U(a certificate CertU) Service provider S {U, CU, CertU, SID}PubKS

Authors: Kui Ren, Wenjing Lou, Kwangjo Kim, and Robert Deng