Trust - Peer-to-Peer Computing: Applications, Architecture, Protocols, and Challenges - page 145

6.7 SuperTrust
Dimitriou et al. [Dimitriou et al., 2007] recently proposed an interesting
scheme called SuperTrust. A novel feature of SuperTrust is that the trust
reports are encrypted and are never opened during the submission or aggre-
gation processes, thus guaranteeing privacy, anonymity, fairness, persistence,
and eligibility of transactions.
SuperTrust is a decentralized framework that ensures the security of trust
handling in K-redundant super peer networks. Thus, in some sense, Su-
perTrust is orthogonal to existing trust management systems for ordinary
peers. However, SuperTrust relies on a hybrid network architecture in that it
assumes the existence of some certificate authority (CA) that can generate or
certify special purpose keys and whose public key can be trusted as authentic.
Associated with each peer v in SuperTrust is a chosen set of n super
peers (i.e., aggregators) that are responsible for “collecting” the votes/reports
of other peers that have interacted with v. The aggregators for each peer
are chosen by the CA amongst the K super peers responsible for the various
clusters. Furthermore, in each cluster, the CA delegates a storage node chosen
amongst the K super peers to act as a storage facility for the reputations
of the peers/resources located in the corresponding cluster (alternatively, as
suggested by Dimitriou et al., this role can be assumed by the aggregators,
thus eliminating single point of failure in the system).
Such a semi-centralized, semi-distributed approach guarantees that each
aggregator peer is within a fixed number of hops from each peer, thereby po-
tentially improving the overall performance of the system. The various actions
of a peer v in SuperTrust are outlined below (see Figure 6.11) [Dimitriou et al.,
2007]:
Step 1: Send a file request. Peer v isssues a request for resource r. Upon
reception of v's request, one of the super peers responsible for v's cluster
broadcasts this request to their neighbors.
Step 2: Receive a list of relevant peers. Upon reception of v's request,
each super peer checks whether the resource requested is within its clus-
ter. Peer u issues a reply confirming his/her possession of the requested
resource. In addition, each of n aggregators of u partially decrypts the
encrypted trust value of u using a (t, n) Paillier-based threshold cryp-
tosystem [Paillier, 1999], and responds to v with their decrypted shares
allowing v to compute the final trust value.
Step 3: Select a set of peers. Once peer v receives the replies and the de-
crypted shares from a su cient number t of aggregators, it calculates
the global trust value of the replying peers and chooses to download the
resource from the most reputable peer.