<p>This master’s thesis consists of a scenario-based evaluation of an IT-security assessment method known as the eXtendedMethod for Assessment of System Security (XMASS), as well as an assessment of a real-world network using the softwareimplementation of this method known as the Security AssessmeNT Application (SANTA).This thesis also describes a number of improvements made to the software implementation, some which could also be addedto the method itself. These were performed during the preparation of the assessment but had no effect on the outcome.The evaluation showed that the method and implementation contained a number of flaws in the way the filtering effect ofthe traffic mediators of a network, such as network-based firewalls, was implemented. When it comes to the assessment ofthe real-world network it was seen that the network, given the supplied information regarding the software and hardwaresetup of its entities, appeared to be sufficiently secure to handle the transmission of data at the lowest classification level(Restricted). However, as with almost all security assessments, this does not mean that the network is guaranteed to besecure enough; it just indicates that, given the information specified, the network has the potential of being sufficientlysecure.The main conclusion of this thesis is that the way XMASS and SANTA calculates the effect of filtering traffic mediatorsshould be looked into and improved to increase the usability of the tool. The method can however still be used in its currentstate, but requires the individual(s) performing the assessment to be aware of the drawbacks of the current implementationand thus compensate for these when producing the input for the assessment method.</p>

This master’s thesis consists of a scenario-based evaluation of an IT-security assessment method known as the eXtendedMethod for Assessment of System Security (XMASS), as well as an assessment of a real-world network using the softwareimplementation of this method known as the Security AssessmeNT Application (SANTA).This thesis also describes a number of improvements made to the software implementation, some which could also be addedto the method itself. These were performed during the preparation of the assessment but had no effect on the outcome.The evaluation showed that the method and implementation contained a number of flaws in the way the filtering effect ofthe traffic mediators of a network, such as network-based firewalls, was implemented. When it comes to the assessment ofthe real-world network it was seen that the network, given the supplied information regarding the software and hardwaresetup of its entities, appeared to be sufficiently secure to handle the transmission of data at the lowest classification level(Restricted). However, as with almost all security assessments, this does not mean that the network is guaranteed to besecure enough; it just indicates that, given the information specified, the network has the potential of being sufficientlysecure.The main conclusion of this thesis is that the way XMASS and SANTA calculates the effect of filtering traffic mediatorsshould be looked into and improved to increase the usability of the tool. The method can however still be used in its currentstate, but requires the individual(s) performing the assessment to be aware of the drawbacks of the current implementationand thus compensate for these when producing the input for the assessment method.

The Swedish Defence Research Agency, FOI, has developed a platform that is used to train and study IT-security. This platform was used during the cyber Baltic shield, an international cyber security exercise. During the exercise, a number of teams acting as system administrators, tried to secure and defend the system of a fictive power supply company. Another team acted as a terrorist organisation with the goal to compromise the systems of the power supply companies and shut down their power generators. FOI has also developed a security assessment method, named XMASS, which is implemented in a software tool called SANTA. This can be used to model a networked IT-system and get a picture of its current state of security. This thesis aims to integrate the tool, SANTA, with the platform for cyber security exercises to get the ability to visualise a system and analyse its security during an IT-security exercise. The thesis also identifies some problems with XMASS regarding how traffic mediators, for example firewalls, are modelled. A literature review is performed to get a picture of the current state of research on security assessment methods and leads to a proposition of a new model for traffic mediators.