what-when-how
In Depth Tutorials and Information
and resist attack fully, although it can contribute to system security. Other compo-
nents are needed such as authentication and identity management.
11.4.2 SocialTrust [15]
In Reference 15 another trust model called
SocialTrust
is proposed. It also has a rep-
utation for tamper resistance. SocialTrust provides community nodes with dynamic
trust values by (1) distinguishing relationship quality from trust, (2) incorporating
a personalized feedback mechanism for adapting as the community evolves, and (3)
tracking user behaviors [15]. hese features are embodied in three components in
the SocialTrust model [15] as shown in (2).
t
1
∫
'
( , )
(11.2)
= ⋅
α
+ ⋅
β
+
γ
⋅
Tr i t
Trust i t
( , )
Tr i t
( , )
Trust i x dx
( ,
)
q
q
t
0
In Equation 11.2,
i
is denoted as a node
i
, and
t
represents time.
1. Quality Component of Trust [
Tr
q
(
i,t
)] represents the current trustworthiness
of the node. As a basic trust metric, quality component of trust is the most
important in the SocialTrust model.
∑
=
λ
⋅
+ −
λ
Tr i
( )
L j Tr
( )
( )
j
rel
( )
j
(
1
)
F i
(
)
(11.3)
q
q
∈
j rel i
( )
In Equation 11.3,
rel
(
i
)
z
represents node
i
's set of relationships and |
rel
(
i
)
|
is
the total number of node
i
's relationships.
hree main factors should be taken into account in trust establishment [15].
a. Trust Establishment Scope: It defines which nodes in STN a node can
judge.
b. Trust Group Feedback:
F
(
i
) is denoted as the feedback rating, which can
be obtained by a voting scheme.
c. Relationship Link Quality: Link Quality
L
(
i
) of a node depends upon the
node's direct relationship links and possibly its neighbors' relationship
links until several hops away. We can use the feedback rating along the
relationship chain to calculate
L
(
i
) iteratively.
λ
is used to adjust the weight of feedback rating and link quality on trust
establishment.
\
≡
t
Trust i x dx
represents the evolution
of the trustworthiness of a node. It makes the nodes tend to behave well over
a long time. Besides, the history component of trust leads to more accurate
computation of the current trust value.
Trust
(
i,x
) is denoted as the trust rat-
ing of a node
i
at time t.
2. History Component of Trust
[
1 4
0
( ,
)
]
3. Adaptation to Change Component of Trust [
Tr'
q
(
i,t
)] is used to track changes of
the behaviors of a node and detect the nodes that suddenly turn malicious.
