Usually, a proof of a theorem contains more knowledge than the mere fact that the theorem is true. For instance, to prove that a graph is Hamiltonian it suffices to exhibit a Hamiltonian tour in it; however, this seems to contain more knowledge than the single bit Hamiltonian/non-Hamiltonian.In this paper a computational complexity theory of the “knowledge” contained in a proof is developed. Zero-knowledge proofs are defined as those proofs that convey no additional knowledge other than the correctness of the proposition in question. Examples of zero-knowledge proof systems are given for the languages of quadratic residuosity and 'quadratic nonresiduosity. These are the first examples of zero-knowledge proofs for languages not known to be efficiently recognizable.

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The knowledge complexity of interactive proof-systems

/pdf/robust-sos-specifications-of-probabilistic-processes-157s6nh401.pdf

Robust SOS Specifications of Probabilistic Processes

With the prevalence and development of GNSS technologies, location-based vehicle services (LBVS) have experienced a rapid growth in recent years. However, location is a sensitive and private piece of information, so the design and development of such services just take the clients' privacy concerns into account. In this paper, we propose a new electronic toll pricing system based on group signatures, which provides a strong guarantee for the clients' anonymity within groups. Our system achieves a balance between privacy and the communication overhead imposed upon the users.

A Group Signature Based Electronic Toll Pricing System

This paper studies the boundedness and termination problems for vector addition systems equipped with one stack. We introduce an algorithm, inspired by the Karp & Miller algorithm, that solves both problems for the larger class of well-structured pushdown systems. We show that the worst-case running time of this algorithm is hyper-Ackermannian for pushdown vector addition systems. For the upper bound, we introduce the notion of bad nested words over a well-quasi-ordered set, and we provide a general scheme of induction for bounding their lengths. We derive from this scheme a hyper-Ackermannian upper bound for the length of bad nested words over vectors of natural numbers. For the lower bound, we exhibit a family of pushdown vector addition systems with finite but large reachability sets (hyper-Ackermannian).

/pdf/hyper-ackermannian-bounds-for-pushdown-vector-addition-2wmrkvmlva.pdf

Hyper-Ackermannian bounds for pushdown vector addition systems

Pushdown systems (PDSs) model single-thread recursive programs, and well-structured transition systems (WSTSs), such as vector addition systems, are useful to represent non-recursive multi-thread programs. Combining these two ideas, our goal is to investigate well-structured pushdown systems (WSPDSs), pushdown systems with well-quasi-ordered control states and stack alphabet.

This paper focuses on subclasses of WSPDSs, in which the coverability becomes decidable. We apply WSTS-like techniques on classical P-automata. A Post*-automata (resp. Pre*-automata) construction is combined with Karp-Miller acceleration (resp. ideal representation) to characterize the set of successors (resp. predecessors) of given configurations. As examples, we show that the coverability is decidable for recursive vector addition system with states, multi-set pushdown systems, and a WSPDS with finite control states and well-quasi-ordered stack alphabet.

/pdf/well-structured-pushdown-systems-1ge78wdzhx.pdf

Well-Structured pushdown systems

In this paper we propose a metric for finite processes in a probabilistic extension of CSP. The kernel of the metric corresponds to trace equivalence and most of the operators in the process algebra is shown to satisfy non-expansiveness property with respect to this metric. We also provide an algorithm to calculate the distance between two processes to a prescribed discount factor in polynomial time. The algorithm has been implemented in a tool that helps us to measure processes automatically.

/pdf/towards-automatic-measurement-of-probabilistic-processes-1k35acj8fx.pdf

Towards Automatic Measurement of Probabilistic Processes

Untraceabilityand unreuseabilityare essential security properties for electronic cash protocols. Many protocols have been proposed to meet these two properties. However, most of them have not been formally proved to be untraceable and unreuseable. In this paper we propose to use the applied pi calculus as a framework for describing and analyzing electronic cash protocols, and we analyze Ferguson's electronic cash protocol as a case study. We believe that this approach is suitable for many different electronic cash protocols.

/pdf/analyzing-an-electronic-cash-protocol-using-applied-pi-1qpiokx8g5.pdf

Analyzing an Electronic Cash Protocol Using Applied Pi Calculus

This paper proposes a new timed model named nested timed automata (NeTAs). A NeTA is a pushdown system whose stack symbols are timed automata (TAs). It either behaves as the top TA in the stack, or switches from one TA to another by pushing, popping, or changing the top TA of the stack. Different from existing component-based context-switch models such as recursive timed automata and timed recursive state machines, when time passage happens, all clocks of TAs in the stack elapse uniformly. We show that the safety property of NeTAs is decidable by encoding NeTAs to the dense timed pushdown automata. NeTAs provide a natural way to analyze the recursive behaviors of component-based timed systems with structure retained. We illustrate this advantage by the deadline analysis of nested interrupts.

/pdf/nested-timed-automata-1fpckevcdb.pdf

Nested timed automata

This paper investigates a general framework of a pushdown system with well-quasi-ordered states and stack alphabet to show decidability of reachability, which is an extension of our earlier work (Well-structured Pushdown Systems, CONCUR 2013). As an instance, an alternative proof of the decidability of the reachability for dense-timed pushdown system (in P.A. Abdulla, M.F. Atig, F. Stenman, Dense-Timed Pushdown Automata, IEEE LICS 2012) is presented. Our proof would be more robust for extensions, e.g., regular valuations with time.

http://www.jaist.ac.jp/~mizuhito/papers/conference/FLOPS14.pdf

Xiaojuan Cai

Papers

Well-Structured pushdown systems

Towards Automatic Measurement of Probabilistic Processes

Analyzing an Electronic Cash Protocol Using Applied Pi Calculus

Nested timed automata

Well-Structured Pushdown System: Case of Dense Timed Pushdown Automata