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a more expensive TN approach that does not directly disclose credentials or
policies is always an option.
5.3 Trust Negotiation Implementations
To date, research on TN has focused mainly on the theoretical issues in-
volved in the negotiation process. While most of the trust management ap-
proaches discussed in this chapter have been implemented, and many of them
have broken interesting new ground in their implementations, very few of
them have been publicly released. Most implementations have been designed
as proofs of concept, and were never intended to be used heavily in prac-
tice. These theoretical works and proofs of concept have been quite suc-
cessful, and thus researchers must now begin to address the implementa-
tion constraints that act as barriers to the deployment of these systems.
Among the systems that support bilateral trust establishment, only Trust-
Builder (http://isrl.cs.byu.edu), TrustBuilder2 (http://dais.cs.uiuc.edu/tn),
and Trust-
χ
(http://www.cs.purdue.edu/homes/squiccia/trustx) are cur-
rently freely available for download. As TrustBuilder2 was built specifically
as a platform for others to reuse and adapt for their own experiments with
TN, we describe it briefly here.
TrustBuilder2 is a flexible and reconfigurable Java-based framework for
supporting research on the systems aspects of TN approaches to authorization.
In TrustBuilder2, the primary components of a TN system—such as strategy
modules, compliance checkers, query interfaces, and audit modules—are rep-
resented using abstract interfaces, as shown in the architectural diagram in
Figure 6. Any or all of these component interfaces can be implemented or
extended by users of the TrustBuilder2 system, thereby making the system's
functionality extensible. The TrustBuilder2 configuration files can be modified
to load these custom components in place of the default system components;
this facilitates code reuse and the incorporation of new features without mod-
ifications to the underlying runtime system. Further, TrustBuilder2 supports
the interposition of user-defined plug-ins at communication points between
system components to allow for easy monitoring of system activity or the
modification of messages passed between components.
The TrustBuilder2 framework provides an environment for researchers to
begin considering the technical issues surrounding the deployment of trust
negotiation protocols in production environments and makes several contri-
butions within this space. In addition to the aspects of flexibility described
above, the abstract type interfaces used by TrustBuilder2 for representing
policies, credentials, and resources ensure that new policy languages, cre-
dential formats, and the inclusion of new evidence types can be supported
without requiring modifications to existing system components or changes to
the TrustBuilder2 framework. This allows users to rapidly implement support
for new features, and also provides a framework within which the trade-offs
