# Strong current-state and initial-state opacity of discrete-event systems

arXiv: https://arxiv.org/abs/2109.05475 · HTML: https://mlsanity.com/paper/2109.05475/

## Key facts

- Cited by 2 papers in the map (data through 14 Oct 2026).
- First posted on arXiv 12 Sep 2021.

## Built on by (most cited first, 2 of 2)

- [Information-Theoretic Opacity-Enforcement in Markov Decision Processes](https://mlsanity.com/paper/2405.00157/) (2024)
- [Policy Gradient Methods for Information-Theoretic Opacity in Markov Decision Processes](https://mlsanity.com/paper/2511.02704/) (2025)

## Abstract (arXiv)

Opacity, as an important property in information-flow security, characterizes the ability of a system to keep some secret information from an intruder. In discrete-event systems, based on a standard setting in which an intruder has the complete knowledge of the system's structure, the standard versions of current-state opacity and initial-state opacity cannot perfectly characterize high-level privacy requirements. To overcome such a limitation, in this paper we propose two stronger versions of opacity in partially-observed discrete-event systems, called strong current-state opacity and strong initial-state opacity. Strong current-state opacity describes that an intruder never makes for sure whether a system is in a secret state at the current time, that is, if a system satisfies this property, then for each run of the system ended by a secret state, there exists a non-secret run whose observation is the same as that of the previous run. Strong initial-state opacity captures that the visit of a secret state at the initial time cannot be inferred by an intruder at any instant. Specifically, a system is said to be strongly initial-state opaque if for each run starting from a secret state, there exists a non-secret run of the system that has the same observation as the previous run has. To verify these two properties, we propose two information structures using a novel concurrent-composition technique, which has exponential-time complexity O(|X|4|Sigmao||Sigmauo||Sigma|2|X|), where |X| (resp., |Sigma|, |Sigmao|, |Sigmauo|) is the number of states (resp., events, observable events, unobservable events) of a system.