Information Technology Reference
In-Depth Information
These requirements lead us to the following exemplary recursive function, in-
spired by the PageRank:
+ e r ( i =1
1
T A ( N i ))
T A ( N X )=
d ( N A , N X )
direct−trust−factor
reputation−factor
T A ( N X ):
Trust Value of a node X from node A's perspective
d ( N A ,N X ):
Distance between node A and node X
r :
Reputation weight parameter
To calculate the trust value of a node X, T A ( N X ) , the length of the shortest
path to node X is determined. Then the reputations factor corrects the value de-
pending on its reputation. The parameter r can be chosen individual in order to
weight the importance of the reputation factor. In our example r=0.75.
To demonstrate this function, an example is provided. Figure 5 shows an
exemplary Web of Trust. The paths show directed trust relations, derived from
observation or confirmation. In Figure 6 it is evident that the trust value in-
creases (the trust level decreases), while moving away from the root node A.
Node C has the highest level, apart from the root, because it is very near to A
and has a high reputation in the web. Node B however has a considerably lower
level, because there are no other trust paths but the one from Node A (Fig-
ure 7). Node F has a comparatively high trust level since there are trust paths
from high level nodes (C and G) although it has no direct relation to the root.
From node B's perspective, the trust values are different. Node A for example
has a significant low level compared to the other nodes, because the transitive
trust path has a length of 4.
Since observation and confirmation are rated equally in this metric, the ober-
vation could be renounced during the enrollment process. In this case, a profile
is untrusted at the beginning. The scope of an untrusted profile however must
be restricted until the authenticity is proved by confirmation. This supports sce-
narios where a minimum level of enrollment security (and quality) is required.
Fig. 6. Trust Values (Perspective A)
Fig. 7. Trust Values (Perspective B)
Search WWH ::




Custom Search