=Paper=
{{Paper
|id=None
|storemode=property
|title=A Trust and Reputation Framework
|pdfUrl=https://ceur-ws.org/Vol-965/paper01-essos2013.pdf
|volume=Vol-965
}}
==A Trust and Reputation Framework==
https://ceur-ws.org/Vol-965/paper01-essos2013.pdf
A Trust and Reputation Framework ∗
Francisco Moyano
Department of Computer Science, University of Malaga, 29071, Málaga, Spain
moyano@lcc.uma.es
Abstract. The Future Internet is posing new security challenges as their
scenarios are bringing together a huge amount of stakeholders and de-
vices that must interact under unforeseeable conditions. In addition, in
these scenarios we cannot expect entities to know each other beforehand,
and therefore, they must be involved in risky and uncertain collabora-
tions. In order to minimize threats and security breaches, it is required
that a well-informed decision-making process is in place, and it is here
where trust and reputation can play a crucial role. Unfortunately, ser-
vices and applications developers are often unarmed to address trust and
reputation requirements in these scenarios. To overcome this limitation,
we propose a trust and reputation framework that allows developers to
create trust- and reputation-aware applications.
Supervisors: Carmen Fernandez-Gago and Javier Lopez
1 Introduction: Problem and Motivation
Future Internet (FI) scenarios bring together multiple entities, namely stakehold-
ers and devices, that need to collaborate in order to reach their goals. Should
these entities knew each other beforehand, upfront mechanisms could be in place
at design-time in order to ensure that these collaborations have a successful end-
ing for all parties. However, this cannot be assumed. Therefore, it is required to
guarantee a successful ending even under risky and uncertain conditions, which
generally involves making good decisions. These conditions present a breeding
ground for trust.
Even when the concept of trust is not standardized, it is agreed that it
can be a valuable tool to leverage decision-making processes. The concept and
implications of trust are embodied in trust models, which define the rules to
process trust in an automatic or semi-automatic way within a computational
setting. For the last twenty years, many models have been proposed, each one
targeting different contexts and purposes, and with their own particularities.
∗
The research leading to these results have received funding from the European
Community’s Seventh Framework Programme FP7/2007-2013 as part of the Network
of Excellence NESSoS (www.nessos-project.eu) under grant agreement number 256980.
The first author is funded by the Spanish Ministry of Education through the National
F.P.U. Program.
One issue with trust models is that they are usually built on top of an existing
application in an ad-hoc manner in order to match the specific needs of the
application and its environment, limiting the models’ re-usability. Furthermore,
most models do not distinguish explicitly between trust and reputation, nor do
they provide guidelines to combine these notions to yield more solid results.
We believe that this approach is not adequate and that developers should be
provided with some mechanisms to systematically incorporate trust and reputa-
tion models into their services and applications.
The rest of the paper is organized as follows. Section 2 describes the goals
that we are pursuing. In Section 3 we explain the research methodology that is
being followed and discuss the work that has been carried out up to now. Finally,
the conclusions and some lines for future research are presented in Section 4.
2 Aims and Goals
Our main goal is the specification, design and implementation of a development
framework that allows developers to implement trust- and reputation-aware ap-
plications. The framework must expose an Application Programming Interface
(API) in order to make its functionalities accessible, and it must also provide
hot spots where trust models can be customized to fit the application needs.
An important sub-goal that is derived from the main expected contributions
is the provision of insight into trust and reputation. It is often the case that
these concepts are considered as being synonyms or are used interchangeably,
however they are quite different notions that need to be considered separately.
Building a development framework requires performing a domain analysis in the
framework targeted area, in this case, trust and reputation. Not only can this
domain analysis shed light on concepts such as trust or reputation, but also on
the trust models internal workings.
The main expected contribution of this research to the field of Engineering
Secure Software and Systems is two-fold: on the one hand, by providing devel-
opers with a tool like a trust and reputation framework, we foster thinking over
trust and reputation requirements from the very beginning. On the other hand,
as applications are developed by using the framework, trust and reputation mod-
els are naturally incorporated within the application itself, and not as patches
added after-the-fact, as it is the standard nowadays. Thus, trust models can use
all the information available to the application in a more efficient way.
3 Research Methodology
This section summarizes the research methodology that is being followed. It is
divided into six phases, each one further elaborated in its own section. For each
phase, we state whether it is completed or further work needs to be done, and
we also outline their main findings and results.
3.1 Phase 1: Literature Review
Surveys, such as the one by Jøsang, Ismail and Boyd [5] or the one by Ruohomaa
and Kutvonen [11] are the best starting point to obtain a solid knowledge of the
work carried out in trust and reputation over a period of time, and they consti-
tute the main source for the next phase: the domain analysis. Other interesting
contributions include those that provide assistance to developers with creating
trust and reputation implementations. In this direction, we conducted research
on architectural styles [12], frameworks [7] [2] and middlewares [6] [4] where trust
and reputation are the core concept.
Some drawn conclusions are that most works do not provide enough margin
of customization and lack of a framework-oriented approach. In addition, no
existing contributions differentiate between the notions of trust and reputation,
as they tend to focus on just one of them, usually reputation.
Even though this task was already finished, it is required to continuously
check out new interesting papers.
3.2 Phase 2: Domain Analysis
A domain analysis is of paramount importance when building a development
framework [3], and for this analysis to be complete, it may be required to look
up new literature that helps to fill some gaps that may have arisen.
The main contribution is a conceptual framework that gathers and relates
the most important concepts in trust and reputation models. This framework is
represented in the form of UML diagrams, like the one depicted in Figure 1. As
explained in an earlier contribution [8], this conceptual framework also serves as
a comparison framework under which different trust and reputation models can
be compared.
1..*
Role
Provision Access Identiy Infrastructure
plays
Trustee's Entities Witness Trustor Trustee
Objective
2
Properties 2..*
Trustee's Trust Class Purpose
1..* instantiates
Subjective Trusted Third
Requester Provider
Properties Party
Trustor's computes has has
Objective Factors Trust relates Trust
Properties Trust Model Relationship
influence establishes 1..* Policy Model
Trustor's has Trust Decision
Subjective Model
Properties Negotiation
Modeling uses
Model
Context Method
Behaviour
1..* Model
Trust
Evaluation Reputation
Mathematic Graphic Linguistic Assumptions
Model Model
Propagation
Model
Fig. 1: Common Concepts for Trust Models
Also, in our earlier work [8], we classified trust models into two types: decision
models, tightly related to the authorization problem, and evaluation models,
where the evaluation of trust according to several influencing factors is the most
important consideration.
Even though this phase is also completed, the analysis should be refined as
new relevant papers arise.
3.3 Phase 3: Requirements Elicitation
The previous phase conducted an exhaustive analysis on trust and reputation.
This analysis assisted in determining the requirements that a trust and repu-
tation framework must fulfil. Since accommodating all possible trust models in
a single framework may be a daunting task, we decided to focus on evaluation
models. A list of requirements can be found in an earlier work [10].
Even though this phase is finalized, some new requirements may arise as
a consequence of new relevant literature or due to the architecture and design
phases. One of our findings is that evaluation models are centred around the
notion of trust metric. Trust metric uses a computation engine to yield a trust
or reputation value given a set of variables. The difference between many eval-
uation models stems from (i) the variables used in the computation and (ii) the
computation engine used to aggregate these variables into a simple value or a
tuple of values. Therefore, one of the most important requirements for a trust
and reputation framework is to allow developers to define their own metrics.
Time and uncertainty are two important factors as well, and developers should
be allowed to include them. The former may be used to consider freshness in
trust values, whereas the latter refers to how reliable a trust value is.
3.4 Phase 4: Architecture
This phase consists of sketching the high-level software structure that supports
the requirements elicited in the previous phase. A half-way technical and concep-
tual architecture was discussed in earlier works [10] [9]. A recent work1 provides
greater insight into the technical details of a possible architecture, and even
guidelines are given for implementation of some of the components and their
communication mechanisms.
At the architectural level, building a trust and reputation framework requires
planning in two fronts. On the one hand, we need to carefully design an easy
yet flexible API that allows connecting any application to a trust server. On
the other hand, the framework must provide enough hot spots to support the
customization of the trust server behaviour at runtime in order to accommodate
new trust and reputation models.
The type of application that we want to build by using the framework de-
termines the design of the aforementioned factors: API and hot spots. In this
1
We cannot provide the reference as the work is currently under review.
sense, we think of two types of applications that follow two different architectural
styles: client-server applications and peer-to-peer applications.
The first one requires the developer to define the interactions between an
application server and a trust server, and the trust server holds information
about the whole system. In the second approach, each peer holds an instance of
the trust server, which holds only partial information about the whole system.
The architecture proposed in our recent work1 was originally designed to
support the client-server approach, even though we think it can be tailored in
order to support the peer-to-peer architectural style.
3.5 Phase 5: Design and Implementation
This phase elaborates on the architecture in order to refine the components into
sub-components and modules. Inner data structures are also detailed and the
database schemas and tables are fully specified. This refinement goes on until
the implementation of each module is made easy. This phase remains unfinished.
3.6 Phase 6: Validation
The last phase consists of validating the framework implementation by develop-
ing a trust-aware application in the scope of e-Health and/or SmartGrid, which
have been identified as the two main NESSoS2 scenarios [1].
It is likely that we observe certain deficiencies and limitations of the frame-
work in a real application. Actually, any framework requires iterations in order
to be able to accommodate a wide range of applications. Therefore, the output of
this phase could help to improve the architecture and design of the framework.
4 Conclusions and Future Work
New Future Internet applications will need support from trust and reputation
services for their successful adoption. Yet these services have been laid aside and
are very often considered once an application is already deployed and running.
At that moment, adding trust and reputation features may be hard, and may
lead to poor and, above all, barely reusable solutions.
We propose a trust framework that assists developers in the task of creating
services and applications that need trust and reputation models. Examples of
such applications are those proposed in the NESSoS project, and validation is
to be done in their scope.
As future work, we are planning to research on how reconfiguration mecha-
nisms can leverage trust models during the service or application lifetime. The
trend in Software Engineering is towards adapting the software at runtime to
new requirements or new environmental conditions, changing the architecture
itself without the need for re-implementation. We would like to obtain insight
into how the trust framework could exploit advances in this direction in order
to support self-adapting trust models.
2
www.nessos-project.eu
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