16 research outputs found
On the Expressiveness of Intensional Communication
The expressiveness of communication primitives has been explored in a common
framework based on the pi-calculus by considering four features: synchronism
(asynchronous vs synchronous), arity (monadic vs polyadic data), communication
medium (shared dataspaces vs channel-based), and pattern-matching (binding to a
name vs testing name equality). Here pattern-matching is generalised to account
for terms with internal structure such as in recent calculi like Spi calculi,
Concurrent Pattern Calculus and Psi calculi. This paper explores intensionality
upon terms, in particular communication primitives that can match upon both
names and structures. By means of possibility/impossibility of encodings, this
paper shows that intensionality alone can encode synchronism, arity,
communication-medium, and pattern-matching, yet no combination of these without
intensionality can encode any intensional language.Comment: In Proceedings EXPRESS/SOS 2014, arXiv:1408.127
On the semantics of Alice&Bob specifications of security protocols
AbstractIn the context of security protocols, the so-called Alice&Bob notation is often used to describe the messages exchanged between honest principals in successful protocol runs. While intuitive, this notation is ambiguous in its description of the actions taken by principals, in particular with respect to the conditions they must check when executing their roles and the actions they must take when the checks fail.In this paper, we investigate the semantics of protocol specifications in Alice&Bob notation. We provide both a denotational and an operational semantics for such specifications, rigorously accounting for these conditions and actions. Our denotational semantics is based on a notion of incremental symbolic runs, which reflect the data possessed by principals and how this data increases monotonically during protocol execution. We contrast this with a standard formalization of the behavior of principals, which directly interprets message exchanges as sequences of atomic actions. In particular, we provide a complete characterization of the situations where this simpler, direct approach is adequate and prove that incremental symbolic runs are more expressive in general. Our operational semantics, which is guided by the denotational semantics, implements each role of the specified protocol as a sequential process of the pattern-matching spi calculus
On the Expressiveness of Joining
The expressiveness of communication primitives has been explored in a common
framework based on the pi-calculus by considering four features: synchronism
(asynchronous vs synchronous), arity (monadic vs polyadic data), communication
medium (shared dataspaces vs channel-based), and pattern-matching (binding to a
name vs testing name equality vs intensionality). Here another dimension
coordination is considered that accounts for the number of processes required
for an interaction to occur. Coordination generalises binary languages such as
pi-calculus to joining languages that combine inputs such as the Join Calculus
and general rendezvous calculus. By means of possibility/impossibility of
encodings, this paper shows coordination is unrelated to the other features.
That is, joining languages are more expressive than binary languages, and no
combination of the other features can encode a joining language into a binary
language. Further, joining is not able to encode any of the other features
unless they could be encoded otherwise.Comment: In Proceedings ICE 2015, arXiv:1508.04595. arXiv admin note:
substantial text overlap with arXiv:1408.145
On Global Types and Multi-Party Session
Global types are formal specifications that describe communication protocols
in terms of their global interactions. We present a new, streamlined language
of global types equipped with a trace-based semantics and whose features and
restrictions are semantically justified. The multi-party sessions obtained
projecting our global types enjoy a liveness property in addition to the
traditional progress and are shown to be sound and complete with respect to the
set of traces of the originating global type. Our notion of completeness is
less demanding than the classical ones, allowing a multi-party session to leave
out redundant traces from an underspecified global type. In addition to the
technical content, we discuss some limitations of our language of global types
and provide an extensive comparison with related specification languages
adopted in different communities
Theory and tool support for the formal verification of cryptographic protocols
Cryptographic protocols are an essential component of network communications. Despite their relatively small size compared to other distributed algorithms, they are known to be error-prone. This is due to the obligation to behave robustly in the context of unknown hostile attackers who might want to act against the security objectives of the jointly interacting entities. The need for techniques to verify the correctness of cryptographic protocols has stimulated the development of new frameworks and tools during the last decades. Among the various models is the spi calculus: a process calculus which is an extension of the pi calculus that incorporates cryptographic primitives. Process calculi such as the spi calculus offer the possibility to describe in a precise and concise way distributed algorithms such as cryptographic protocols. Moreover, spi calculus offers an elegant way to formalise some security properties of cryptographic protocols via behavioural equivalences. At the time this thesis began, this approach lacked tool support. Inspired by the situation in the pi calculus, we propose a new notion of behavioural equivalence for the spi calculus that is close to an algorithm. Besides, we propose a "coq" formalisation of our results that not only validates our theoretical developments but also will eventually be the basis of a certified tool that would automate equivalence checking of spi calculus terms. To complete the toolchain, we propose a formal semantics for an informal notation to describe cryptographic protocols, so called protocol narrations. We give a rigorous procedure to translate protocol narrations into spi calculus terms; this constitutes the foundations of our automatic translation tool "spyer"
A Taxonomy for and Analysis of Anonymous Communications Networks
Any entity operating in cyberspace is susceptible to debilitating attacks. With cyber attacks intended to gather intelligence and disrupt communications rapidly replacing the threat of conventional and nuclear attacks, a new age of warfare is at hand. In 2003, the United States acknowledged that the speed and anonymity of cyber attacks makes distinguishing among the actions of terrorists, criminals, and nation states difficult. Even President Obama’s Cybersecurity Chief-elect recognizes the challenge of increasingly sophisticated cyber attacks. Now through April 2009, the White House is reviewing federal cyber initiatives to protect US citizen privacy rights. Indeed, the rising quantity and ubiquity of new surveillance technologies in cyberspace enables instant, undetectable, and unsolicited information collection about entities. Hence, anonymity and privacy are becoming increasingly important issues. Anonymization enables entities to protect their data and systems from a diverse set of cyber attacks and preserves privacy. This research provides a systematic analysis of anonymity degradation, preservation and elimination in cyberspace to enhance the security of information assets. This includes discovery/obfuscation of identities and actions of/from potential adversaries. First, novel taxonomies are developed for classifying and comparing well-established anonymous networking protocols. These expand the classical definition of anonymity and capture the peer-to-peer and mobile ad hoc anonymous protocol family relationships. Second, a unique synthesis of state-of-the-art anonymity metrics is provided. This significantly aids an entity’s ability to reliably measure changing anonymity levels; thereby, increasing their ability to defend against cyber attacks. Finally, a novel epistemic-based mathematical model is created to characterize how an adversary reasons with knowledge to degrade anonymity. This offers multiple anonymity property representations and well-defined logical proofs to ensure the accuracy and correctness of current and future anonymous network protocol design
Logical concepts in cryptography
This thesis is about a breadth-first exploration of logical concepts in cryptography and their linguistic abstraction and model-theoretic combination in a comprehensive logical system, called CPL (for Cryptographic Protocol Logic). We focus on two fundamental aspects of cryptography. Namely, the security of communication (as opposed to security of storage) and cryptographic protocols (as opposed to cryptographic operators). The primary logical concepts explored are the following: the modal concepts of belief, knowledge, norms, provability, space, and time. The distinguishing feature of CPL is that it unifies and refines a variety of existing approaches. This feature is the result of our wholistic conception of property-based (modal logics) and model-based (process algebra) formalisms