Over the recent years, the protection of the so-called `soft-targets', i.e. locations easily accessible by the general public with relatively low, though, security measures, has emerged as a rather challenging and increasingly important issue. The complexity and seriousness of this security threat growths nowadays exponentially, due to the emergence of new advanced technologies (e.g. Artificial Intelligence (AI), Autonomous Vehicles (AVs), 3D printing, etc.); especially when it comes to large-scale, popular and diverse public spaces. In this paper, a novel Digital Twin-as-a-Security-Service (DTaaSS) architecture is introduced for holistically and significantly enhancing the protection of public spaces (e.g. metro stations, leisure sites, urban squares, etc.). The proposed framework combines a Digital Twin (DT) conceptualization with additional cutting-edge technologies, including Internet of Things (IoT), cloud computing, Big Data analytics and AI. In particular, DTaaSS comprises a holistic, real-time, large-scale, comprehensive and data-driven security solution for the efficient/robust protection of public spaces, supporting: a) data collection and analytics, b) area monitoring/control and proactive threat detection, c) incident/attack prediction, and d) quantitative and data-driven vulnerability assessment. Overall, the designed architecture exhibits increased potential in handling complex, hybrid and combined threats over large, critical and popular soft-targets. The applicability and robustness of DTaaSS is discussed in detail against representative and diverse real-world application scenarios, including complex attacks to: a) a metro station, b) a leisure site, and c) a cathedral square.

翻译：近年来，所谓"软目标"（即公众易于进入且安防措施相对薄弱的场所）的防护已成为一项极具挑战性且日益重要的议题。随着人工智能、自动驾驶车辆、3D打印等新兴先进技术的出现，针对大规模、高人气、多元化的公共空间的安全威胁，其复杂性与严重性正呈指数级增长。本文提出一种创新的数字孪生安全即服务架构，旨在系统性地显著提升地铁站、休闲场所、城市广场等公共空间的防护水平。该框架将数字孪生概念与物联网、云计算、大数据分析和人工智能等前沿技术相结合，构建出实时、大规模、综合性、数据驱动的安全解决方案，具备以下核心功能：a) 数据采集与分析，b) 区域监控与主动威胁检测，c) 事件/攻击预测，d) 量化数据驱动的脆弱性评估。总体而言，该架构在处理针对大型关键软目标的复杂混合型威胁方面展现出显著潜力。本文通过地铁站、休闲场所、教堂广场等典型现实场景下的复合攻击案例，详细论证了该架构的适用性与鲁棒性。