Semantic communication (SemCom) has emerged as a promising paradigm for future wireless networks by prioritizing task-relevant meaning over raw data delivery, thereby reducing communication overhead and improving efficiency. However, shifting from bit-accurate transmission to task-oriented delivery introduces new security and privacy risks. These include semantic leakage, semantic manipulation, knowledge base vulnerabilities, model-related attacks, and threats to authenticity and availability. Most existing secure SemCom studies focus on analog SemCom, where semantic features are mapped to continuous channel inputs. In contrast, digital SemCom transmits semantic information through discrete bits or symbols within practical transceiver pipelines, offering stronger compatibility with real-world systems while exposing a distinct and underexplored attack surface. In particular, digital SemCom typically represents semantic information over a finite alphabet through explicit digital modulation, following two main routes: probabilistic modulation and deterministic modulation. These discrete mechanisms and practical transmission procedures introduce additional vulnerabilities affecting bit- or symbol-level semantic information, the modulation stage, and packet-based delivery and protocol operations. Motivated by these challenges and the lack of a systematic analysis of secure digital SemCom, this paper provides a structured review of the area. Specifically, we review SemCom fundamentals and clarify the architectural differences between analog and digital SemCom. We then summarize threats shared by both paradigms and organize the threat landscape specific to digital SemCom, followed by a discussion of potential defenses. Finally, we outline open research directions toward secure and deployable digital SemCom systems.

翻译：语义通信作为一种面向未来无线网络的新型范式，通过优先传输任务相关的语义信息而非原始数据，有效降低了通信开销并提升了传输效率。然而，从比特精确传输转向任务导向的语义传递也引入了新的安全与隐私风险，包括语义泄露、语义篡改、知识库漏洞、模型相关攻击以及对真实性与可用性的威胁。现有大多数安全语义通信研究集中于模拟语义通信，即将语义特征映射为连续信道输入。相比之下，数字语义通信在实际收发器链路中通过离散比特或符号传输语义信息，在提升与现有系统兼容性的同时，也暴露出独特且尚未被充分探索的攻击面。具体而言，数字语义通信通常通过显式数字调制在有限字符集上表示语义信息，主要遵循两条技术路线：概率调制与确定性调制。这些离散化机制及实际传输流程引入了额外的脆弱环节，可能影响比特/符号级语义信息、调制阶段以及基于分组的传输与协议操作。基于上述挑战及当前缺乏对安全数字语义通信的系统性分析，本文对该领域进行了结构化综述。具体而言，我们回顾语义通信的基础原理，阐明模拟与数字语义通信在架构上的差异；总结两类范式共同面临的安全威胁，并系统梳理数字语义通信特有的威胁图景；进而探讨潜在的防御机制。最后，我们展望了构建安全可部署数字语义通信系统的开放研究方向。