In this paper, we study an information flow security property for systems specified as terms of a quantitative Markovian process algebra, namely the Performance Evaluation Process Algebra (PEPA). We propose a quantitative extension of the Non-Interference property used to secure systems from the functional point view by assuming that the observers are able to measure also the timing properties of the system, e.g., the response time of certain actions or its throughput. We introduce the notion of Persistent Stochastic Non-Interference (PSNI) based on the idea that every state reachable by a process satisfies a basic Stochastic Non-Interference (SNI) property. The structural operational semantics of PEPA allows us to give two characterizations of PSNI: one based on a bisimulation-like equivalence relation inducing a lumping on the underlying Markov chain, and another one based on unwinding conditions which demand properties of individual actions. These two different characterizations naturally lead to efficient methods for the verification and construction of secure systems. A decision algorithm for PSNI is presented and an application of PSNI to a queueing system is discussed.

中文翻译：

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持续随机不干涉

在本文中，我们研究了指定为定量马尔可夫过程代数，即性能评估过程代数 (PEPA) 项的系统的信息流安全属性。我们通过假设观察者也能够测量系统的时间属性，例如某些动作的响应时间或其吞吐量，从功能的角度提出用于保护系统的非干扰属性的定量扩展。我们基于进程可到达的每个状态都满足基本的随机不干扰 (SNI) 属性的想法引入了持久随机不干扰 (PSNI) 的概念。PEPA 的结构操作语义允许我们给出 PSNI 的两个特征：一种基于类似互模拟的等价关系，导致底层马尔可夫链上的集总，另一种基于需要单个动作属性的展开条件。这两种不同的特征自然会导致验证和构建安全系统的有效方法。提出了 PSNI 的决策算法，并讨论了 PSNI 在排队系统中的应用。