TWC: Medium: Limits and Algorithms for Covert Communications

安全和隐私是现代通信中的突出问题。尽管人们已经广泛研究了加密方法来保护消息内容不被窃听者破译，但很多时候隐藏通信的存在是至关重要的。隐藏通信，称为隐蔽（私有）通信，在许多领域都很重要，例如秘密军事行动，以及消除用户在日常活动中被跟踪的能力。同样重要的是，研究如何限制这种秘密通信，例如在恐怖分子等组织活动以造成伤害的各方之间。这个项目的重点是了解秘密通信的潜力，即，有多少信息可以在不被检测的情况下进行通信，以及开发提供秘密通信的实用方案以及限制这种通信的技术。在历史上，秘密通信一直是从实践的角度来考虑的。例如，扩频通信是作为一种提供隐蔽通信的无线通信技术而发展起来的。开发诸如Tor之类的系统是为了在互联网上提供隐蔽性。该项目侧重于系统地研究在现代通信网络的物理层、网络层和应用层提供通信隐蔽性的基本限制。它将探索在无线信道中使用噪声和网络中的定时可变性来实现隐蔽通信。这包括在不被发现的情况下秘密传递的信息量方面制定基本限制，同时考虑到所有参与者之间的不确定性。该项目还将侧重于开发应用级秘密通信的基本限制，使用IP语音和社交网络上的图像发布。一个关键的考虑因素将是这些限制如何受到操作环境变化的影响，包括通信方的盟友有意加强秘密通信或通信方的对手有意限制此类通信的变化。第二个重点将是确保通信各方达到这些限制的算法的设计和评估，以及另一组算法，确保当这些各方试图超过限制时被检测到。

Security and privacy are prominent concerns in modern communications. Although cryptographic approaches have been widely studied to protect a message's content from deciphering by an eavesdropper, there are many times when hiding the very existence of the communication is critical. The hiding of communication, termed covert (private) communication, is important in many domains such as covert military operations, and removing the ability of users to be tracked in their everyday activities. It is also important to study how to limit such covert communications, for example between parties such as terrorists organizing activities to do harm. This project is focused on understanding what the potential is for covert communications, i.e., how much information can be communicated without detection, and the development of practical schemes for providing covert communications as well as techniques for limiting such communication. Covert communication has been historically considered from a practical perspective. For example spread spectrum communications was developed as a wireless communication technique to provide covert communications. Systems such as Tor were developed to provide covertness in the Internet. This project focuses on the systematic investigation of the fundamental limits in providing covertness in communications at the physical, the network, and the application layers of modern communication networks. It will explore the use of noise in wireless channels and timing variabilities in networks to implement covert communications. This includes the development of fundamental limits in terms of the amount of information that can be conveyed covertly without being detected, while accounting for uncertainties among all participants. The project will also focus on the development of fundamental limits for application-level covert communications using voice over IP and image posting on social networks. A key consideration will be how these limits can be impacted by changes in the operating environment, including those changes made intentionally by allies of the communicating parties to enhance covert communications or those made by adversaries of the communicating parties to limit such. A second focus will be on the design and evaluation of algorithms that ensure communicating parties achieve these limits and another set of algorithms that ensure these parties are detected when they attempt to exceed the limits.