tailieunhanh - Mobile Ad Hoc Networks Applications Part 7

Tham khảo tài liệu 'mobile ad hoc networks applications part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Grouping-Enabled and Privacy-Enhancing Communications Schemes for VANETs 201 Fig. 3. Batch verification Batch verification This module allows an RSU to verify a batch of signatures using only two pairing operations based on the bilinear property of the bilinear map. We require an RSU to perform batch verification at a frequency higher than that with which a vehicle broadcasts safety messages so that a vehicle can verify the safety message of another before it broadcasts a more updated one. We first show the verification procedure. Then we show how to make use of bloom filter to construct a notification message in order to reduce the message overhead. Lastly we describe how to handle the case in which there are invalid signatures in the batch and how to extract valid ones from the batch instead of dropping the whole batch as in Zhang Lu Lin Ho Shen 2008 . Verification procedure. Assume that RSU wants to verify a batch of signatures ơ Ữ2 . Un from vehicles Vi V2 . vn on messages Ml M2 . Mn. With the shared secrets and the pseudo identities of the vehicles RSU first determines their verification public keys VPKi VPK2 . VPKn and shared secrets mi m2 . mn by checking which of the stored VPKi mi pairs satisfy IDi2 VPKi H miIDii . It then verifies the signatures by checking if ề Ei i p e n l mtIDti h Mi H lDa Ppub as ể n ifi p e En i SKii h Mi SKi2 p _ ê ỵ SKil p e sn i h Mi SKi2 p ê fn i sm-IDii p ê tn i h Mi sH ID a p ê ỵ milDii sP riti h Mi H IDJ2 sP ê ỵ n i miIDii ppub ê En ih Mi H IDi2 ppub ê Èn i mtIDa h Mi H IDi2 Ppub . To avoid replay attack an RSU stores the pseudo identities used by vehicles. If the pseudo identity in a vehicle s message matches any stored one RSU rejects the message immediately. Note that if a vehicle does not know the shared secret with RSU it cannot produce a valid signature. There may be a very small chance that the pseudo identities generated by two vehicles are the same. In that case RSU will treat the signatures as invalid. The .