Presenter: Hongwei Li

Smart Grid Group Seminar P2: Privacy-Preserving Communication and Precise Reward Architecture for V2G Networks in Smart Grid Presenter: Hongwei Li

Outline • Introduction • System Models • System Design • Security analysis • Performance analysis • Conclusion 2

Introduction • Vehicle-to-grid(V2G) network is a system where parked battery vehicles (BVs) communicate with the smart grid to consume electricity. • In addition, BVs also sell electricity storage capability by delivering electricity to grid as required. • BVs charge during off-peak hours. • BVs discharge during peak hours A good idea How to do?

Introduction • A long-term participation agreement is signed between BVs AND V2G operators. However ! • The fixed connection requirement contained in the long-term agreement will cause inconvenience to the BV owners. • An unexpected earlyleaving from the parking lot. • Some other accidental events. BV owners’ interest in joining the V2G networks are reduced! How to solve this problem! 4

Introduction • A precise reward scheme • Does not require BV owners to sign a long-term contract • Giving the reward to owners in the form of E-cash However, Privcay raising! • The identity and location of BV owners are compromised. • By analyzing the monitoring data of specific BV, such as the parking lots it visited and how long it stayed there, the operator of a V2G network can easily deduce the personal activities of this BV’s owner. • The detailed service record for specific BV could result in privacy leakage too. How to solve these problems! 5

Introduction(Contributions) • The first attempt to identify the privacy protection issues in V2G networks. • A precise and reward scheme for V2G networks. • individual BV is rewarded according to its contribution to each service. • A secure communication architecture • achieves privacy-preserving for both BV’s monitoring and rewarding processes. • pursues important objectives for secure communication, including mutual authentication, confidentiality, data integrity, and so forth.

Outline Introduction System Models System Design Security analysis Performance analysis Conclusion

System Models (Network architecutre ) Fig. 1 Network architecutre 8

System Models (Network model ) Fig.2 Network model of the V2G network 9

System Models (Trust Model and Security Goals) • Trust Model • TA is trusted by all the other parties. There is no direct trust relationship between individual BV and CAG(Central Aggregator) or LAGs (Local Aggregators). • Security Goals • Mutual authentication between BV and aggregator. • Confidentiality and integrity of the communication • Location and identity privacy of BV • Anonymous reward • Efficient revocation of BVs 10

System Design :Initialization • TA initializes the V2G network • Diffie-Hellman (BDH) parameter generator generate the public parameters • Each entity , including all the BVs, LAGs, and CAG, submits its ID information to TA to get its public/private key pair.

System Design :Permit-Based Access Control and BV’s Monitoring • Permit Generation • BV obtains the permit by restrictive partially blind signature . Why? • To ensure that verifier can not link BV’s real identity with this permit when it sees the permit later.

System Design :Permit-Based Access Control and BV’s Monitoring Fig.3 Permit Generation Algorithm 14

System Design :Permit-Based Access Control and BV’s Monitoring • Permit Verification: • When accessing the V2G network, each BV presents a permit and a • pseudonym PS to the LAG (local aggregators). 15

System Design :Permit-Based Access Control and BV’s Monitoring • Permit-Based Access Control and BV’s Monitoring • After Permit Verification, a session key will be used in the following • communication between this BV and LAG. • When the next monitoring cycle comes, this BV reports its current status ST to the LAG. After collecting STs for this monitoring period • from all the BVs in the local area. • LAG forwards them to the CAG(central aggregator) in batch mode. Since each ST is identified by pseudonym PS , both the LAG and CAG • could not link the monitoring data with the real identity of the BV. 16

System Design :Anonymous Service Providing and Rewarding After receiving those monitoring data from LAGs, CAG computes the current available electricity storage capacity and makes bids for providing some services which are publicly requested by smart grid in the electricity market.

System Design :BV’s Revocation • Consider two types of revocations. • In the first case, if the operator of the V2G network wants to revoke a BV’s right to access the V2G network, what it needs to do is just deny this BV’s new requests for permit. • In another case, the BV is compromised. The BV needs to report all its permits . the operator will immediately notify all LAGs to deny all attempts to access the V2G network.

Security analysis • Location and identity privacy of BV. • Due to the adoption of restrictive partially blind signature technique in the generation of permit, the LAG which verified the permit can not deduce the BV’s real identity from the permit and the related pseudonym, even with the help of CAG. • Further, for each pair of permit and pseudonym, a BV only uses it within single parking period, thus LAGs can not link a specific BV’s multiple parking activities with the same BV..

Security analysis • Anonymity and incontestability of the reward. • To protect the identity privacy of the well-behaved BVs and at the same time keep the capability of tracing BVs which commit double redeeming, the generation of reword, similar as that of the permit, also adopts the restrictive partially blind signature technique. 21

Security analysis • Basic security requirements. • The scheme can also achieve security objectives, including mutual authenticaition between BV and aggregators, confidentiality of the communications, validation of the communicating messages, • Through the adoption of the standard cryptographic primitives: namely, symmetric key-based encryption, secure hashed message authentication, digital signature. The use of timestamp in all the communicating messages could effectively prevent replay attack. 22

Performance analysis • Computation: • BV • generation process: 8 pairings+9 exponentiations on G+ 9 scalar multiplications G1. • Monitoring process: BV needs to periodically report its current status to LAG. Those reports will be encrypted with AES. this will incur negligible computational cost for BV. • Aggregator • CAG needs to do 4 pairings + 5 scalar multiplications for the generation of single permit and reward, respectively. • In the verification process of permitand the redeeming process of permit, Aggregators need to do 6 pairings, 5 exponentiations, and 1 scalar multiplication. • These operations will be scattered throughout the whole day. In addition, considering that those aggregators are dedicated equipment with cloud computing. 24

Performance analysis • Communication: • The communication overhead incurred by mostly comes from the periodical monitoring. • where each BV needs to report its current status ST to LAG. Since the information contained in the ST only occupies very short message (no larger than 100 bytes) and the period of reporting is usually several or even tens of seconds. • this communication overhead is totally tolerable for current communication techniques. 25

Conclusion • The first attempt to identify and formulate the privacy protection and precise reward problems in V2G networks, both of which are important for bring the V2G concept into practice. • A secure and privacy- preserving communication and precise reward architecture for V2G networks, • not only provide satisfiable privacy protection and precise reward to the BVs. • but also achieves other important security objectives including mutual authentication, confidential communication, data integrity, etc.

Thank you ! 27

Presenter: Hongwei Li