The emergence of the Internet of Agents (IoA) introduces critical challenges for communication privacy in sensitive, high-stakes domains. While standard Agent-to-Agent (A2A) protocols secure message content, they are not designed to protect the act of communication itself, leaving agents vulnerable to surveillance and traffic analysis. We find that the rich, event-driven nature of agent dialogues provides a powerful, yet untapped, medium for covert communication. To harness this potential, we introduce and formalize the Covert Event Channel, the first unified model for agent covert communication driven by three interconnected dimensions, which consist of the Storage, Timing,and Behavioral channels. Based on this model, we design and engineer ΠCCAP, a novel protocol that operationalizes this event-driven paradigm. Our comprehensive evaluation demonstrates that ΠCCAP achieves high capacity and robustness while remaining imperceptible to powerful LLM-based wardens, establishing its practical viability. By systematically engineering this channel, our work provides the foundational understanding essential for developing the next generation of monitoring systems and defensive protocols for a secure and trustworthy IoA.

翻译：智能体互联网（IoA）的兴起为敏感、高风险领域的通信隐私带来了关键挑战。尽管标准的智能体间（A2A）协议能够保障消息内容的安全，但其设计并未保护通信行为本身，使得智能体容易受到监控和流量分析。我们发现，智能体对话丰富的事件驱动特性为隐蔽通信提供了一个强大但尚未被利用的媒介。为挖掘这一潜力，我们引入并形式化了隐蔽事件通道，这是首个由三个相互关联维度驱动的智能体隐蔽通信统一模型，这三个维度包括存储通道、时序通道和行为通道。基于此模型，我们设计并实现了ΠCCAP协议，这是一种将事件驱动范式操作化的新型协议。我们的综合评估表明，ΠCCAP在保持对基于大语言模型的强大监控者不可感知的同时，实现了高容量和高鲁棒性，证明了其实用可行性。通过对该通道的系统性工程化，我们的工作为开发下一代监控系统及防御协议、构建安全可信的智能体互联网提供了必不可少的基础性理解。