Cost-aware Runtime Enforcement of Security Policies

In runtime enforcement of security policies, the classic requirements on monitors in order to enforce a security policy are soundness and transparency. However, there are many monitors that successfully pass this specification but they differ in complexity of both their implementation and the output they produce. In order to distinguish and compare these monitors we propose to associate cost with enforcement. We present a framework where the cost of enforcement of a trace is determined by the cost of operations the monitor uses to edit the trace. We explore cost-based order relations on sound monitors. We investigate cost-optimality of monitors which allows considering the most cost-efficient monitors that soundly enforce a property

There are Two Sides to Every Question - Controller Versus Attacker.

We investigate security enforcement mechanisms that run in parallel with a system; the aim is to check and modify the run-time behaviour of a possible attacker in order to guarantee that the system satisfies some security policies. We focus on a CSP-like quantitative process-algebra to model such processes. Weights on actions are modelled with semirings, which represent a parametric structure where to cast different metrics. The basic tools are represented by a quantitative logic and a model checking function. First, the behaviour of the system is removed from the parallel computation with respect to some security property to be satisfied. Secondly, what remains is refined in two formulas with respect to the given operator executed by a controller. The result describes what a controller has to do to prevent a given attack

Semiring-based Specification Approaches for Quantitative Security

Our goal is to provide different semiring-based formal tools for the specification of security requirements: we quantitatively enhance the open-system approach, according to which a system is partially specified. Therefore, we suppose the existence of an unknown and possibly malicious agent that interacts in parallel with the system. Two specification frameworks are designed along two different (but still related) lines. First, by comparing the behaviour of a system with the expected one, or by checking if such system satisfies some security requirements: we investigate a novel approximate behavioural-equivalence for comparing processes behaviour, thus extending the Generalised Non Deducibility on Composition (GNDC) approach with scores. As a second result, we equip a modal logic with semiring values with the purpose to have a weight related to the satisfaction of a formula that specifies some requested property. Finally, we generalise the classical partial model-checking function, and we name it as quantitative partial model-checking in such a way to point out the necessary and sufficient conditions that a system has to satisfy in order to be considered as secure, with respect to a fixed security/functionality threshold-value

Quantitative evaluation of enforcement strategies

In Security, monitors and enforcement mechanisms run in parallel with programs to check, and modify their run-time behaviour, respectively, in order to guarantee the satisfaction of a security policy. For the same pol- icy, several enforcement strategies are possible. We provide a framework for quantitative monitoring and enforcement. Enforcement strategies are analysed according to user-dened parameters. This is done by extending the notion controller processes, that mimics the well-known edit automata, with weights on transitions, valued in a C-semiring. C-semirings permit one to be exible and general in the quantitative criteria. Furthermore, we provide some examples of orders on controllers that are evaluated under incomparable criteria