OASIS: Weakening User Obligations for Security-critical Systems

Security-critical systems typically place some requirements on the behaviour of their users, obliging them to follow certain instructions when using those systems. Security vulnerabilities can arise when users do not fully satisfy their obligations. In this paper, we propose an approach that improves system security by ensuring that attack scenarios are mitigated even when the users deviate from their expected behaviour. The approach uses structured transition systems to present and reason about user obligations. The aim is to identify potential vulnerabilities by weakening the assumptions on how the user will behave. We present an algorithm that combines iterative abstraction and controller synthesis to produce a new software specification that maintains the satisfaction of security requirements while weakening user obligations. We demonstrate the feasibility of our approach through two examples from the e-voting and e-commerce domains.