Verification of temporal-epistemic properties of access control systems

Verification of access control systems against vulnerabilities has always been a challenging problem in the world of computer security. The complication of security policies in large- scale multi-agent systems increases the possible existence of vulnerabilities as a result of mistakes in policy definition. This thesis explores automated methods in order to verify temporal and epistemic properties of access control systems. While temporal property verification can reveal a considerable number of security holes, verification of epistemic properties in multi-agent systems enable us to infer about agents' knowledge in the system and hence, to detect unauthorized information flow. This thesis first presents a framework for knowledge-based verification of dynamic access control policies. This framework models a coalition-based system, which evaluates if a property or a goal can be achieved by a coalition of agents restricted by a set of permissions defined in the policy. Knowledge is restricted to the information that agents can acquire by reading system information in order to increase time and memory efficiency. The framework has its own model-checking method and is implemented in Java and released as an open source tool named \char{cmmi10}{0x50}\char{cmmi10}{0x6f}\char{cmmi10}{0x6c}\char{cmmi10}{0x69}\char{cmmi10}{0x56}\char{cmmi10}{0x65}\char{cmmi10}{0x72}. In order to detect information leakage as a result of reasoning, the second part of this thesis presents a complimentary technique that evaluates access control policies over temporal-epistemic properties where the knowledge is gained by reasoning. We will demonstrate several case studies for a subset of properties that deal with reasoning about knowledge. To increase the efficiency, we develop an automated abstraction refinement technique for evaluating temporal-epistemic properties. For the last part of the thesis, we develop a sound and complete algorithm in order to identify information leakage in Datalog-based trust management systems

Comparison of the effects of transcranial direct current stimulation and mindfulness-based stress reduction on mental fatigue, quality of life and aggression in mild traumatic brain injury patients: a randomized clinical trial

Abstract Background The rate of traumatic brain injuries (TBIs) due to the accidents is high around the world. Patients with mild TBIs may suffer from some psychological disorders, including aggression, and mental fatigue, and thus their quality of life decreased. Among different treatments for TBI, two treatments, namely transcranial direct current stimulation (tDCS), and mindfulness-based stress reduction (MBSR) have shown to be effective. Therefore, this study aimed to compare the effects of these two treatments on mental fatigue, aggression and quality of life in mTBI patients. Materials and methods This randomized controlled trial study was conducted on 48 TBI patients referred to emergency and neurosurgery departments of Shahid Beheshti Hospital, Kashan, Iran. They were selected using the convenience sampling method. Data were collected using the mental fatigue scale, the World Health Organization Quality of Life-BREF (short version), and the Buss–Perry Aggression Questionnaires. Then, the data were analyzed using a Mixed Repeated Measures ANOVAs, and the Levene and Kolmogorov–Smirnov tests by SPSS-23 software. Results The mean age of patients in the three groups of MBSR, tDCS and control were 69.38 + 6.11 (25% male), 25.40 + 12.11 (25% male) and 69.37 + 0.2 (18.8% male), respectively. There was no significant difference between the three groups in terms of mental fatigue, quality of life and aggression (P < 0.05). In addition, the results showed that there was a significant difference between the main effect of time and the interaction between time and group (P < 0.001). Conclusions Both MBSR and tDCS methods are effective in reducing the mental fatigue and aggression and increasing quality of life of mTBI patients; MBSR treatment, as indicated in the present study, can be more effective than tDCS in patients with mTBI. Trial registration : Thailand Registry of Clinical Trials, TCTR20180827003 Registered on August 24, 2018