Scyther : semantics and verification of security protocols

Recent technologies have cleared the way for large scale application of electronic communication. The open and distributed nature of these communications implies that the communication medium is no longer completely controlled by the communicating parties. As a result, there has been an increasing demand for research in establishing secure communications over insecure networks, by means of security protocols. In this thesis, a formal model for the description and analysis of security protocols at the process level is developed. At this level, under the assumption of perfect cryptography, the analysis focusses on detecting aws and vulnerabilities of the security protocol. Starting from ??rst principles, operational semantics are developed to describe security protocols and their behaviour. The resulting model is parameterized, and can e.g. capture various intruder models, ranging from a secure network with no intruder, to the strongest intruder model known in literature. Within the security protocol model various security properties are de??ned, such as secrecy and various forms of authentication. A number of new results about these properties are formulated and proven correct. Based on the model, an automated veri??cation procedure is developed, which signi ??cantly improves over existing methods. The procedure is implemented in a prototype, which outperforms other tools. Both the theory and tool are applied in two novel case studies. Using the tool prototype, new results are established in the area of protocol composition, leading to the discovery of a class of previously undetected attacks. Furthermore, a new protocol in the area of multiparty authentication is developed. The resulting protocol is proven correct within the framework

APTE: An Algorithm for Proving Trace Equivalence

This paper presents APTE, a new tool for automatically proving the security of cryptographic protocols. It focuses on proving trace equivalence between processes, which is crucial for specifying privacy type properties such as anonymity and unlinkability. The tool can handle protocols expressed in a calculus similar to the applied-pi calculus, which allows us to capture most existing protocols that rely on classical cryptographic primitives. In particular, APTE handles private channels and else branches in protocols with bounded number of sessions. Unlike most equivalence verifier tools, APTE is guaranteed to terminate Moreover, APTE is the only tool that extends the usual notion of trace equivalence by considering ``side-channel'' information leaked to the attacker such as the length of messages and the execution times. We illustrate APTE on different case studies which allowed us to automatically (re)-discover attacks on protocols such as the Private Authentication protocol or the protocols of the electronic passports

A reduced semantics for deciding trace equivalence using constraint systems

Many privacy-type properties of security protocols can be modelled using trace equivalence properties in suitable process algebras. It has been shown that such properties can be decided for interesting classes of finite processes (i.e., without replication) by means of symbolic execution and constraint solving. However, this does not suffice to obtain practical tools. Current prototypes suffer from a classical combinatorial explosion problem caused by the exploration of many interleavings in the behaviour of processes. M\"odersheim et al. have tackled this problem for reachability properties using partial order reduction techniques. We revisit their work, generalize it and adapt it for equivalence checking. We obtain an optimization in the form of a reduced symbolic semantics that eliminates redundant interleavings on the fly.Comment: Accepted for publication at POST'1

Part 2: A Pilot Ethnomethodological Study

This second paper reports on a small ethnographic study of Argentine psychiatrists. A carefully selected group of six psychiatrists currently practicing in Buenos Aires par- ticipated in an in-depth semi-structured interview. The transcripts of the interviews were coded and a thematic analysis method was applied to construct a local theory of the professional values constructed by Argentine psy- chiatrists, and the circumstances in which such values were constructed. Our analysis indicated that Argentine psychia- trists constructed a number of values, frequently perceived as obligations to their professional group and the needs of their patients. The two main strategies employed by Ar- gentine psychiatrists were the diagnostic act and advocacy. We also identify that these values emerge in the context of recent broad historical and cultural influences upon the profession of psychiatry in Argentina, and the Argentine population in general

Verifying parameterized timed security protocols

Quantitative timing is often explicitly used in systems for better security, e.g., the credentials for automatic website logon often has limited lifetime. Verifying timing relevant security protocols in these systems is very challenging as timing adds another dimension of complexity compared with the untimed protocol verification. In our previous work, we proposed an approach to check the correctness of the timed authentication in security protocols with fixed timing constraints. However, a more difficult question persists, i.e., given a particular protocol design, whether the protocol has security flaws in its design or it can be configured secure with proper parameter values? In this work, we answer this question by proposing a parameterized verification framework, where the quantitative parameters in the protocols can be intuitively specified as well as automatically analyzed. Given a security protocol, our verification algorithm either produces the secure constraints of the parameters, or constructs an attack that works for any parameter values. The correctness of our algorithm is formally proved. We implement our method into a tool called PTAuth and evaluate it with several security protocols. Using PTAuth, we have successfully found a timing attack in Kerberos V which is unreported before.No Full Tex