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08:30-09:00Coffee & Refreshments
09:00-10:30 Session 100B: Information Flow
Location: Taub 2
IFCIL: An Information Flow Configuration Language for SELinux

ABSTRACT. Security Enhanced Linux (SELinux) is a security architecture for Linux implementing mandatory access control. It has been used in numerous security-critical contexts ranging from servers to mobile devices. But this is challenging as SELinux security policies are difficult to write, understand, and maintain. Recently, the intermediate language CIL was introduced to foster the development of high-level policy languages and to write structured configurations. However, CIL lacks mechanisms for ensuring that the resulting configurations obey desired information flow policies. To remedy this, we propose IFCIL, a backward compatible extension of CIL for specifying fine-grained information flow requirements for CIL configurations. Using IFCIL, administrators can express, e.g., confidentiality, integrity, and non-interference properties. We also provide a tool to statically verify these requirements.

Towards a General-Purpose Dynamic Information Flow Policy

ABSTRACT. Noninterference offers a rigorous end-to-end guarantee for the secure propagation of information. However, real-world systems almost always involve security requirements that change during program execution, making noninterference inapplicable. Prior works alleviate the limitation to some extent, but even for a veteran in information flow security, understanding the subtleties in the syntax and semantics of each policy are challenging, largely due to their very different policy specification languages, and more fundamentally, semantic requirements.

We take a top-down approach and present a novel information flow policy, called Dynamic Release, which allows information flow restrictions to downgrade and upgrade in arbitrary ways. Dynamic Release is formalized on a novel framework that, for the first time, allows us to compare and contrast various dynamic policies in the literature. We show that Dynamic Release generalizes declassification, erasure, endorsement and revocation. Moreover, it is the only dynamic policy that is both applicable and correct on a benchmark of tests with dynamic policy.

Beware of Greeks bearing entanglement? Quantum covert channels, information flow and non-local games

ABSTRACT. Can quantum entanglement increase the capacity of (classical) covert channels? To one familiar with Holevo's Theorem it is tempting to think that the answer is obviously no. However, in this work we show: quantum entanglement can in fact increase the capacity of a classical covert channel, in the presence of an active adversary; on the other hand, a zero-capacity channel is not improved by entanglement, so entanglement cannot create `purely quantum' covert channels; the problem of determining the capacity of a given channel in the presence of entanglement is undecidable; but there is an algorithm to bound the entangled capacity of a channel from above, adapted from the semi-definite hierarchy from the theory of non-local games, whose close connection to channel capacity is at the core of all of our results.

10:30-11:00Coffee Break
11:00-12:30 Session 102B: Security Protocols 2
Location: Taub 2
Cracking the Stateful Nut -- Computational Proofs of Stateful Security Protocols using the Squirrel Proof Assistant
PRESENTER: Adrien Koutsos

ABSTRACT. Bana and Comon have proposed a logical approach to proving protocols in the computational model, which they call the Computationally Complete Symbolic Attacker (CCSA). The proof assistant Squirrel implements a verification technique that elaborates on this approach, building on a meta-logic over the CCSA base logic. In this paper, we show that this meta-logic can naturally be extended to handle protocols with mutable states (key updates, counters, \etc.) and we extend Squirrel's proof system to be able to express the complex proof arguments that are sometimes required for these protocols. Our theoretical contributions have been implemented in Squirrel and validated on a number of case studies, including a proof of the YubiKey and YubiHSM protocols.

Exploiting Partial Order of Keys to Verify Security of a Vehicular Group Protocol
PRESENTER: Felipe Boeira

ABSTRACT. Vehicular networks will enable a range of novel applications to enhance road traffic efficiency, safety, and reduce fuel consumption. As for other cyber-physical systems, security is essential to the deployment of these applications and standardisation efforts are ongoing. In this paper, we perform a systematic security evaluation of a vehicular platooning protocol through a thorough analysis of the protocol and security standards. We tackle the complexity of the resulting model with a proof strategy based on a relation on keys. The key relation forms a partial order, which encapsulates both secrecy and authenticity dependencies. We show that our order-aware approach makes the verification feasible and proves authenticity properties along with secrecy of all keys used throughout the protocol.

Symbolic protocol verification with dice: process equivalences in the presence of probabilities
PRESENTER: Steve Kremer

ABSTRACT. Symbolic protocol verification generally abstracts probabilities away, considering computations that succeed only with negligible probability, such as guessing random numbers or breaking an encryption scheme, as impossible. This abstraction, sometimes referred to as the perfect cryptography assumption, has shown very useful as it simplifies automation of the analysis. However, probabilities may also appear in the control flow where they are generally not negligible. In this paper we consider a framework for symbolic protocol analysis with a probabilistic choice operator: the probabilistic applied pi calculus. We define and explore the relationships between several behavioral equivalences. In particular we show the need for randomized schedulers and exhibit a counter-example to a result in a previous work that relied on non-randomized ones. As in other frameworks that mix both non-deterministic and probabilistic choices, schedulers may sometimes be unrealistically powerful. We therefore consider two subclasses of processes that avoid this problem. In particular, when considering purely non-deterministic protocols, as is done in classical symbolic verification, we show that a probabilistic adversary has---maybe surprisingly---a strictly superior distinguishing power for may testing, which, when the number of sessions is bounded, we show to coincide with purely possibilistic similarity.

12:30-14:00Lunch Break

Lunches will be held in Taub lobby (CAV, CSF) and in The Grand Water Research Institute (DL, NMR, IJCAR, ITP).

14:00-15:30 Session 104B: Invited Talk 2
Location: Taub 2
So near and yet so far: formal verification of distance bounding protocols

ABSTRACT. In the context of contactless systems, obtaining reliable information about physical proximity is of paramount importance. For example, when a person performs a cryptographic identification protocol at the entrance to a building, we would want to be sure that the person giving the answers is no more than a few feet away. With regard to contactless payment, it is important to ensure that the transaction is carried out by the credit card in the vicinity of the reader.

The research community in logics, program verification, and security has a long tradition in developing techniques and tools to analyse security protocols such as key establishment and authentication protocols. Distance bounding protocols which are used to provide secure proximity control, raise new challenges. In this talk, we will present some distance bounding protocols, the security properties they are intented to achieve, and review the types of fraud that can be perpetrated against these protocols. We will then present recent results that render possible the formal symbolic analysis of distance bounding protocols, as well as an overview of the results obtained on various distance bounding protocols in the literature. Despite the recent progress, some limitations remain and they will be discussed at the end of the talk.

16:00-16:30Coffee Break
16:30-17:30 Session 108: Plenary
SMT-based Verification of Distributed Network Control Planes

ABSTRACT. The network control plane is a complex distributed system that runs various protocols for exchanging messages between routers and selecting paths for routing traffic. Errors in control plane configurations can lead to expensive outages or critical security breaches. The last decade has seen tremendous advances in applying formal methods to ensure their correctness.

In this talk, I will describe our logic-based approach that leverages Satisfiability Modulo Theory (SMT) solvers to verify a wide variety of network correctness properties including reachability, fault-tolerance, router equivalence, and load balancing. Although this approach is general and powerful, and works well for small-sized networks (with a few hundred routers), there are scalability challenges. I will then describe some recent improvements based on key abstractions and modular assume-guarantee reasoning that have enabled our SMT-based approach to successfully handle large-sized networks (with several thousands of routers), similar to those in operation in modern data centers.

This talk describes joint work with Ryan Beckett, Ratul Mahajan, Divya Raghunathan, Timothy Alberdingk Thijm, and David Walker.