Have you ever asked yourself some of the following
- Should I worry when using my credit card on the Internet?
- How safe is my Internet bank account?
- How many doctors or healthcare personnel have access to my personal health records?
- Can I be sure that I am the only one reading my e-mail?
- How crucial can a single personal mistake be for my company?
A security risk analysis may provide answers to such
questions. CORAS is a method for conducting security risk
analysis. CORAS provides a
customised language for threat and risk modelling, and
comes with detailed guidelines explaining how the language
should be used to capture and model relevant information
during the various stages of the security analysis. In this
respect CORAS is model-based. The Unified Modelling Language
(UML) is typically used to model the target of the
analysis. For documenting intermediate results, and for
presenting the overall conclusions we use special CORAS
diagrams which are inspired by UML. The CORAS method
provides a computerised tool
designed to support
documenting, maintaining and reporting analysis results
through risk modelling.
In the CORAS method a security risk analysis is conducted in
The eight steps of the CORAS method are summarised as follows.
- Step 1: The first step is the initial
preparations for a risk analysis. The main objective is to
get a basic idea about what is to be the target and what
will be the size of the analysis such that we can make the
necessary preparations for the actual analysis tasks.
- Step 2: The second step is the introductory
meeting with the customer on the behalf of which the
analysis is conducted. The main item on the agenda for
this meeting is to get the representatives of the customer
to present their overall goals of the analysis and the
target they wish to have analysed. The objective is to
achieve a common initial understanding of the target of
analysis, and of what the parties of the analysis are most
concerned about. The overall goals of the analysis are put
forward, the focus and scope of the analysis are set, and
the rest of the analysis is planned.
- Step 3: The thirds step aims to ensure a common
understanding of the target of analysis, including its
focus, scope and main assets. The analysis team presents
their understanding of what they learned at the first
meeting and from studying documentation that has been made
available to them by the customer. Based on interaction
with the customer, the analysis team will also identify
the main assets to be protected. The analysis team
furthermore conducts a rough, high-level analysis to
identify major threat scenarios, vulnerabilities and
enterprise level risks that should be investigated
further. The outcome of Step 3 is a refined and more
detailed understanding of the target description and the
objectives of the analysis, which at this point are
documented by the analysts.
- Step 4: The fourth step aims to ensure that the
background documentation for the rest of the analysis,
including the target, focus and scope is correct and
complete as seen by the customer. The step involves
presenting a more refined description of the target to be
analysed, including assumptions and preconditions being
made. Typically, the analysts describe the target using a
formal or semi-formal notation such as the UML. Before the
actual risk analysis starts at the next step of the
analysis process, the description of the target should be
approved by the customer. Step 4 furthermore includes
deciding the risk evaluation criteria for each asset. This
analysis step concludes the context establishment.
- Step 5: The fifth step is the risk
identification. To identify risks, CORAS makes use of
structured brainstorming. Structured brainstorming is a
step-by-step walkthrough of the target of analysis and is
carried out as a workshop led by the analysts. The main
idea of structured brainstorming is that since the
workshop participants represent different competences,
backgrounds and interests, they will view the target from
different perspectives and consequently identify more, and
possibly other, risks than individuals or a more
homogeneous group would have managed. The risk
identification involves a systematic identification of
threats, unwanted incidents, threat scenarios and
vulnerabilities with respect to the identified assets. The
activities are supported by the CORAS language, and the
results are documented on-the-fly by means of CORAS threat
- Step 6: The sixth step aims to determine the
risk level of the risks that are represented by the
identified unwanted incidents. The unwanted incidents were
documented in threat diagrams during Step 5, and these
diagrams serve as the basis for the risk estimation. Step
6 is conducted as a brainstorming involving personnel with
various backgrounds, and basically involves the estimation
of the likelihoods and consequences of the unwanted
incidents. These values in combination yield the risk
level for each of the identified risks. The CORAS threat
diagrams facilitate the likelihood estimation by
supporting the estimation of the likelihood for threats
and threat scenarios to cause the unwanted incidents.
- Step 7: The seventh step aims to decide which
of the identified risks are acceptable, and which of the
risks must be further evaluated for possible
treatment. Whether or not the risks are acceptable is
determined by using the already defined risk evaluation
criteria and the results of the risk estimation. Step 7
furthermore involves estimating and evaluating risks with
respect to indirect assets.
- Step 8: The eighth step is concerned with the
identification and analysis of treatments. The risks that
are found to be unacceptable are evaluated to find means
to reduce them. A treatment should contribute to reduced
likelihood and/or consequence of an unwanted
incident. Since treatments can be costly, they are
assessed with respect to their cost-benefit, before a
final treatment plan is made.
2013-12-28 A new version of the formal semantics
for the CORAS modeling language is now available. Whereas
the previous semantics was based on probabilities and
probability reasoning, the new version supports reasoning
about likelihoods using frequencies and frequency
intervals. In the practical setting of risk modeling and
analysis, frequencies are more adequate and suitable than
probabilities. The new semantics can be found in the
of a technical report.
For an introduction to CORAS, Chapter 3 of the CORAS book
(A Guided Tour of the CORAS Method) can
for free from Springer. See also
flyer for information about the book.
Description of the CORAS
tool and instructions on how to get started using the
tool has been made available. The instructions include a
demo video that shows the basic use and features.
CORAS on LinkedIn. The LinkedIn Group for the CORAS
approach to model-driven risk analysis offers a medium to
discuss risk analysis in general and issues of relevance
to CORAS in particular.
A CORAS tutorial will be given on April 24 at
the Cyber Security &
Privacy (CSP) EU Forum 2012 in Berlin, Germany.