82,512 research outputs found
Liveness of Randomised Parameterised Systems under Arbitrary Schedulers (Technical Report)
We consider the problem of verifying liveness for systems with a finite, but
unbounded, number of processes, commonly known as parameterised systems.
Typical examples of such systems include distributed protocols (e.g. for the
dining philosopher problem). Unlike the case of verifying safety, proving
liveness is still considered extremely challenging, especially in the presence
of randomness in the system. In this paper we consider liveness under arbitrary
(including unfair) schedulers, which is often considered a desirable property
in the literature of self-stabilising systems. We introduce an automatic method
of proving liveness for randomised parameterised systems under arbitrary
schedulers. Viewing liveness as a two-player reachability game (between
Scheduler and Process), our method is a CEGAR approach that synthesises a
progress relation for Process that can be symbolically represented as a
finite-state automaton. The method is incremental and exploits both
Angluin-style L*-learning and SAT-solvers. Our experiments show that our
algorithm is able to prove liveness automatically for well-known randomised
distributed protocols, including Lehmann-Rabin Randomised Dining Philosopher
Protocol and randomised self-stabilising protocols (such as the Israeli-Jalfon
Protocol). To the best of our knowledge, this is the first fully-automatic
method that can prove liveness for randomised protocols.Comment: Full version of CAV'16 pape
ROYALE: A Framework for Universally Composable Card Games with Financial Rewards and Penalties Enforcement
While many tailor made card game protocols are known, the vast majority of those suffer from three main issues: lack of mechanisms for distributing financial rewards and punishing cheaters, lack of composability guarantees and little flexibility, focusing on the specific game of poker. Even though folklore holds that poker protocols can be used to play any card game, this conjecture remains unproven and, in fact, does not hold for a number of protocols (including recent results). We both tackle the problem of constructing protocols for general card games and initiate a treatment of such protocols in the Universal Composability (UC) framework, introducing an ideal functionality that captures general card games constructed from a set of core card operations. Based on this formalism, we introduce Royale, the first UC-secure general card games which supports financial rewards/penalties enforcement. We remark that Royale also yields the first UC-secure poker protocol. Interestingly, Royale performs better than most previous works (that do not have composability guarantees), which we highlight through a detailed concrete complexity analysis and benchmarks from a prototype implementation
Effects of two different small-sided games protocols on physiological parameters of professional soccer players
The aim of the present study was to evaluate the effect of two different small-sided game protocols on the internal and external training parameters of professional soccer players. Twenty-two (N = 22) Greek Superleague 2 team players (age: 28.69 ± 3.4yr.; stature: 179.0 ± 25 cm; body mass: 76.0 ± 5.6 kg; body fat: 7.68 ± 1.5 %) participated in this study. The small-sided games (SSGs) included two research protocols+: A) 6+6 vs 6+6+2GK (45x40 m; 150m2 per player) with a duration of 4x4 min and B) 10 vs 10+2GK (75x65 m; 244 m2 per player) with a duration of 4x8min. The heart rate of the players, the covered distances, the amount of sprints and the number of accelerations/decelerations were recorded during the above protocols via short-range radio telemetry (Polar Team Sports System). The t-test (paired samples) was used to compare the differences between the two SSGs protocols. The results showed that the 6+6 vs 6+6+2GK SSGs induced significantly higher heart rate in relation to the 10 vs 10+2GK SSGs (p < .05). Furthermore, during the 10 vs 10+2GK SSGs the players covered more distances with high speed, while during the 6+6 vs 6+6+2GK SSGs a great number of accelerations and decelerations were recorded. Summarizing, the studied SSGs protocols resulted in different physical adaptations regarding the intensity, endurance and strength of the professional players. Thus, the trainers should carefully select the appropriate program focusing on the orientation of their training and the expected results
Single-qubit loss-tolerant quantum position verification protocol secure against entangled attackers
Protocols for quantum position verification (QPV) which combine classical and
quantum information are insecure in the presence of loss. We study the exact
loss-tolerance of the most popular protocol for QPV, which is based on BB84
states, and generalizations of this protocol. By bounding the winning
probabilities of a variant of the monogamy-of-entanglement game using
semidefinite programming (SDP), we find tight bounds for the relation between
loss and error for these extended non-local games.
These new bounds enable the usage of QPV protocols using more-realistic
experimental parameters. We show how these results transfer to the variant
protocol which combines bits of classical information with a single qubit,
thereby exhibiting a protocol secure against a linear amount of entanglement
(in the classical information ) even in the presence of a moderate amount of
photon loss. Moreover, this protocol stays secure even if the photon encoding
the qubit travels arbitrarily slow in an optical fiber. We also extend this
analysis to the case of more than two bases, showing even stronger
loss-tolerance for that case.
Finally, since our semi-definite program bounds a monogamy-of-entanglement
game, we describe how they can also be applied to improve the analysis of
one-sided device-independent QKD protocols
Processes, Roles and Their Interactions
Taking an interaction network oriented perspective in informatics raises the
challenge to describe deterministic finite systems which take part in networks
of nondeterministic interactions. The traditional approach to describe
processes as stepwise executable activities which are not based on the
ordinarily nondeterministic interaction shows strong centralization tendencies.
As suggested in this article, viewing processes and their interactions as
complementary can circumvent these centralization tendencies.
The description of both, processes and their interactions is based on the
same building blocks, namely finite input output automata (or transducers).
Processes are viewed as finite systems that take part in multiple, ordinarily
nondeterministic interactions. The interactions between processes are described
as protocols.
The effects of communication between processes as well as the necessary
coordination of different interactions within a processes are both based on the
restriction of the transition relation of product automata. The channel based
outer coupling represents the causal relation between the output and the input
of different systems. The coordination condition based inner coupling
represents the causal relation between the input and output of a single system.
All steps are illustrated with the example of a network of resource
administration processes which is supposed to provide requesting user processes
exclusive access to a single resource.Comment: In Proceedings IWIGP 2012, arXiv:1202.422
Designing Network Protocols for Good Equilibria
Designing and deploying a network protocol determines the rules by which end users interact with each other and with the network. We consider the problem of designing a protocol to optimize the equilibrium behavior of a network with selfish users. We consider network cost-sharing games, where the set of Nash equilibria depends fundamentally on the choice of an edge cost-sharing protocol. Previous research focused on the Shapley protocol, in which the cost of each edge is shared equally among its users. We systematically study the design of optimal cost-sharing protocols for undirected and directed graphs, single-sink and multicommodity networks, and different measures of the inefficiency of equilibria. Our primary technical tool is a precise characterization of the cost-sharing protocols that induce only network games with pure-strategy Nash equilibria. We use this characterization to prove, among other results, that the Shapley protocol is optimal in directed graphs and that simple priority protocols are essentially optimal in undirected graphs
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