Latest Work

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  Formal Analysis of Sneak-Peek: A Data Centre Attack and its Mitigations*

  Attackers can exploit covert channels, such as timing side-channels, to transmit information without data owners or network administrators being aware. Sneak-Peek is a recently considered data centre attack, where, in a multi-tenant setting, an insider attacker can communicate with colluding outsiders by inten- tionally adding delays to traffic on logically isolated but physically shared links. Timing attack mitigations typically introduce delays or randomness which can make it difficult to understand the trade-off between level of security (bandwidth of the covert channel) and performance loss. We demonstrate that formal meth- ods can help. We analyse the impacts of two Sneak-Peek mitigations, namely, noise addition and path hopping. We provide a precise mathematical model of the attack and of the effectiveness these defences. This mathematical analysis is extended by two tool-based stochastic formal models, one formalized in UPPAAL and the other in CARMA. The formal models can capture more general and larger networks than a paper-based analysis, can be used to check properties and make measurements, and are more easily modifiable than conventional network simu- lations. With UPPAAL, we can analyse the effectiveness of mitigations and with CARMA, we can analyse how these mitigations affect latencies in typical data centre topologies. As results, we show that using a selective strategy for path hop- ping is better than a random strategy, that using the two defences in conjunction may actually be worse than using a single defence, and we show the connection between hop frequency and network latency.

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  A Logical Framework with Commutative and Non-Commutative Subexponentials*

  Logical frameworks allow the specification of deductive systems us- ing the same logical machinery. Linear logical frameworks have been success- fully used for the specification of a number of computational, logics and proof systems. Its success lies on the fact that formulas can be distinguished as linear, which behave intuitively as resources, and unbounded, which behave intuitionis- tically. Commutative subexponentials enhance the expressiveness of linear logic frameworks by allowing the distinction of multiple contexts. These contexts may behave as multisets of formulas or sets of formulas. Motivated by applications in distributed systems and in type-logical grammar, we propose a linear logical framework containing both commutative and non-commutative subexponentials. Non-commutative subexponentials can be used to specify contexts which behave as lists, not multisets, of formulas. In addition, motivated by our applications in type-logical grammar, where the weakenening rule is disallowed, we investigate the proof theory of formulas that can only contract, but not weaken. In fact, our contraction is non-local. We demonstrate that under some conditions such formu- las may be treated as unbounded formulas, which behave intuitionistically.

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  On the Accuracy of Formal Verification of Selective Defenses for TDoS Attacks*

  Telephony Denial of Service (TDoS) attacks target telephony services, such as Voice over IP (VoIP), not allowing legitimate users to make calls. There are few defenses that attempt to mitigate TDoS attacks, most of them using IP filtering, with limited applicability. In our previous work, we proposed to use selective strategies for mitigating HTTP Application-Layer DDoS Attacks demonstrating their effectiveness in mitigating different types of attacks.Developing such types of defenses is challenging as there are many design options, \eg, which dropping functions and selection algorithms to use. Our first contribution is to demonstrate both experimentally and by using formal verification that selective strategies are suitable for mitigating TDoS attacks.We used our formal model to help decide which selective strategies to use with much less effort than carrying out experiments. Our second contribution is a detailed comparison of the results obtained from our formal models and the results obtained by carrying out experiments. We demonstrate that formal methods is a powerful tool for specifying defenses for mitigating Distributed Denial of Service attacks allowing to increase our confidence on the proposed defense before actual implementation.

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