An automated model-based test oracle for access control systems

In the context of XACML-based access control systems, an intensive testing activity is among the most adopted means to assure that sensible information or resources are correctly accessed. Unfortunately, it requires a huge effort for manual inspection of results: thus automated verdict derivation is a key aspect for improving the cost-effectiveness of testing. To this purpose, we introduce XACMET, a novel approach for automated model-based oracle definition. XACMET defines a typed graph, called the XAC-Graph, that models the XACML policy evaluation. The expected verdict of a specific request execution can thus be automatically derived by executing the corresponding path in such graph. Our validation of the XACMET prototype implementation confirms the effectiveness of the proposed approach.Comment: 7 page

On Properties of Policy-Based Specifications

The advent of large-scale, complex computing systems has dramatically increased the difficulties of securing accesses to systems' resources. To ensure confidentiality and integrity, the exploitation of access control mechanisms has thus become a crucial issue in the design of modern computing systems. Among the different access control approaches proposed in the last decades, the policy-based one permits to capture, by resorting to the concept of attribute, all systems' security-relevant information and to be, at the same time, sufficiently flexible and expressive to represent the other approaches. In this paper, we move a step further to understand the effectiveness of policy-based specifications by studying how they permit to enforce traditional security properties. To support system designers in developing and maintaining policy-based specifications, we formalise also some relevant properties regarding the structure of policies. By means of a case study from the banking domain, we present real instances of such properties and outline an approach towards their automatised verification.Comment: In Proceedings WWV 2015, arXiv:1508.0338

Automated Certification of Authorisation Policy Resistance

Attribute-based Access Control (ABAC) extends traditional Access Control by considering an access request as a set of pairs attribute name-value, making it particularly useful in the context of open and distributed systems, where security relevant information can be collected from different sources. However, ABAC enables attribute hiding attacks, allowing an attacker to gain some access by withholding information. In this paper, we first introduce the notion of policy resistance to attribute hiding attacks. We then propose the tool ATRAP (Automatic Term Rewriting for Authorisation Policies), based on the recent formal ABAC language PTaCL, which first automatically searches for resistance counter-examples using Maude, and then automatically searches for an Isabelle proof of resistance. We illustrate our approach with two simple examples of policies and propose an evaluation of ATRAP performances.Comment: 20 pages, 4 figures, version including proofs of the paper that will be presented at ESORICS 201

Trust realisation in multi-domain collaborative environments

In the Internet-age, the geographical boundaries that have previously impinged upon inter-organisational collaborations have become decreasingly important. Of more importance for such collaborations is the notion and subsequent nature of trust - this is especially so in Grid-like environments where resources are both made available and subsequently accessed and used by remote users from a multitude of institutions with a variety of different privileges spanning across the collaborating resources. In this context, the ability to dynamically negotiate and subsequently enforce security policies driven by various levels of inter-organisational trust is essential. In this paper we present a dynamic trust negotiation (DTN) model and associated prototype implementation showing the benefits and limitations DTN incurs in supporting n-tier delegation hops needed for trust realisation in multi-domain collaborative environments

Directed Security Policies: A Stateful Network Implementation

Large systems are commonly internetworked. A security policy describes the communication relationship between the networked entities. The security policy defines rules, for example that A can connect to B, which results in a directed graph. However, this policy is often implemented in the network, for example by firewalls, such that A can establish a connection to B and all packets belonging to established connections are allowed. This stateful implementation is usually required for the network's functionality, but it introduces the backflow from B to A, which might contradict the security policy. We derive compliance criteria for a policy and its stateful implementation. In particular, we provide a criterion to verify the lack of side effects in linear time. Algorithms to automatically construct a stateful implementation of security policy rules are presented, which narrows the gap between formalization and real-world implementation. The solution scales to large networks, which is confirmed by a large real-world case study. Its correctness is guaranteed by the Isabelle/HOL theorem prover.Comment: In Proceedings ESSS 2014, arXiv:1405.055

Impersonal efficiency and the dangers of a fully automated securities exchange

This report identifies impersonal efficiency as a driver of market automation during the past four decades, and speculates about the future problems it might pose. The ideology of impersonal efficiency is rooted in a mistrust of financial intermediaries such as floor brokers and specialists. Impersonal efficiency has guided the development of market automation towards transparency and impersonality, at the expense of human trading floors. The result has been an erosion of the informal norms and human judgment that characterize less anonymous markets. We call impersonal efficiency an ideology because we do not think that impersonal markets are always superior to markets built on social ties. This report traces the historical origins of this ideology, considers the problems it has already created in the recent Flash Crash of 2010, and asks what potential risks it might pose in the future