Covert channels are unforeseen and stealthy communication channels that enable manifold adversary scenarios. However, they can also allow the exchange of confidential information by journalists. All covert channels described until now therefore need to craft seemingly legitimate information flows for their information exchange, mimicking unsuspicious behavior. In this paper, we present DYST, which represents a new class of covert channels we call history covert channels jointly with the new paradigm of covert channel amplification. History covert channels can communicate almost exclusively by pointing to unaltered legitimate traffic created by regular network nodes. Only a negligible fraction of the covert communication process requires the transfer of actual covert channel information by the covert channel's sender. This allows, for the first time, an amplification of the covert channel's message size, i.e., minimizing the fraction of actually transferred secret data by a covert channel's sender in relation to the overall secret data being exchanged. We extend the current taxonomy for covert channels to show how history channels can be categorized. We describe multiple scenarios in which history covert channels can be realized, theoretically analyze the characteristics of these channels and show how their configuration can be optimized for different implementations. We further evaluate the robustness and detectability of history covert channels.

翻译：隐蔽信道是不被预见且隐秘的通信信道，可导致多种敌手场景，但也能被记者用于交换机密信息。迄今为止描述的所有隐蔽信道都需要构造看似合法的信息流以进行信息交换，模仿无嫌疑的行为。本文提出DYST，这是一种我们称为历史隐蔽信道的新类别隐蔽信道，同时提出隐蔽信道增强这一新范式。历史隐蔽信道几乎可以完全通过指向常规网络节点生成的未修改合法流量来进行通信。只有极小部分隐蔽通信过程需要由隐蔽信道发送方传输实际的隐蔽信道信息。这首次实现了隐蔽信道消息大小的增强，即最小化隐蔽信道发送方实际传输的秘密数据相对于所交换的总秘密数据的比例。我们扩展了当前隐蔽信道的分类体系，以展示历史信道如何被归类。我们描述了可实现历史隐蔽信道的多种场景，从理论上分析了这些信道的特征，并展示了如何针对不同实现优化其配置。我们进一步评估了历史隐蔽信道的鲁棒性和可检测性。