Despite existing work on dealing with security and usability concerns during the early stages
of design, there has been little work on synthesising the contributions of these fields into
processes for specifying and designing systems. Without a better understanding of how to deal
with both concerns at an early stage, the design process risks disenfranchising stakeholders,
and resulting systems may not be situated in their contexts of use.
The research problem this thesis addresses is how techniques and tools can be integrated and
improved to support the design of usable and secure systems. To develop this understanding,
we present IRIS (Integrating Requirements and Information Security) — a framework for
specifying usable and secure systems. IRIS considers the system design process from three
different perspectives — Usability, Security, and Requirements — and guides the selection of
techniques towards integrative Security, Usability, and Requirements Engineering processes.
This thesis claims that IRIS is an exemplar for integrating existing techniques and tools
towards the design of usable and secure systems. In particular, IRIS makes three significant
contributions towards the stated research problem. First, a conceptual model for usable
secure Requirements Engineering is presented, upon which the IRIS framework is founded;
this meta-model informs changes to elicitation and specification techniques for improved
interoperability in the design process. Second, several characteristics of tool-support needed
to elicit and specify usable and secure systems are introduced; the CAIRIS (Computer Aided
Integration of Requirements and Information Security) software tool is presented to illustrate
how these characteristics can be embodied. Third, we describe how the results of applying
IRIS can be used to improve the design of existing User-Centered Design techniques for secure
systems design.
We validate the thesis by applying the IRIS framework to three case studies. In the first, IRIS
is used to specify requirements for a software repository used by a UK water company. In the
second, IRIS is used to specify security requirements for a meta-data repository supporting
the sharing of medical research data. In the final case study, IRIS is used to analyse a
proposed security policy at a UK water company, and identify missing policy requirements.
In each case study, IRIS is applied within the context of an Action Research intervention,
where findings and lessons from one case study are fed into the action plan of the next.