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6.3 PeerTrust
Xiong and Liu [Xiong and Liu, 2004] proposed the PeerTrust mechanism.
In PeerTrust, similar to prior approaches such as EigenTrust, a peer's trust-
worthiness is defined by an evaluation of the peer it receives in providing
service to other peers in the past. Xiong and Liu identify five important fac-
tors for such evaluation:
1. the feedback a peer obtains from other peers;
2. the feedback scope, such as the total number of transactions that a peer
has with other peers;
3. the credibility factor for the feedback source;
4. the transaction context factor for discriminating mission-critical trans-
actions from less or noncritical ones; and
5. the community context factor for addressing community-related charac-
teristics and vulnerabilities.
Xiong and Liu's approach is based on the notation as shown in Table 6.1.
TABLE 6.1: Notation used in Xiong and Liu's PeerTrust system.
Symbol
Definition
I(u, v)
total number of transactions performed by peer u with v
I(u)
total number of transactions performed by peer u with all
other peers
p(u, i)
other participating peer in peer u's ith transaction
S(u, i)
normalized amount of satisfaction peer u receives from p(u, i)
in its ith transaction
Cr(v)
credibility of the feedback submitted by v
T F (u, i)
adaptive transaction context factor for peer u's ith transaction
CF (u)
adaptive community context factor for peer u
Note: From Xiong and Liu, 2004.
The trust value of peer u denoted by T (u) is then defined as:
I(u)
T (u) = α
S(u, i)Cr(p(u, i))T F (u, i) + βCF (u)
(6.6)
i=1
where α and β denote the normalized weight factors for the collective evalua-
tion and the community context factor. The first part of the trust computation
equation is a weighted average of amount of satisfaction a peer receives for each
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