A covert channel is a communication path that allows transferring information in a way that violates a system security policy. Because of their concealed nature, detecting and preventing covert channels are obligatory security practices. In this paper, we present an examination of network storage channels in the Internet Protocol version 6 (IPv6). We introduce and analyze 22 different covert channels. In the appendix, we define three types of active wardens, stateless, stateful, and network-aware, who differ in complexity and ability to block the analyzed covert channels.

Abstract. Protocol steganography allows users who wish to communicate secretly to embed information within other messages and network control protocols used by common applications. This form of unobservable communication can be used as means to enhance privacy and anonymity as well as for many other purposes, ranging from entertainment to protected business communication or national defense. In this paper, we describe our approach to application-layer protocol steganography, describing how we can embed messages into a commonly used TCP/IP protocol. We also introduce the notions of syntax and semantics preservation, which ensure that messages after embedding still conform to the host protocol. Based on those concepts, we attempt to produce reasonably secure and robust stegosystems. To demonstrate the efficacy of our approach, we have implemented protocol steganography within the Secure Shell (SSH) protocol. Findings indicate that protocol steganographic system is reasonably secure if the statistical profile of the covermessages and the statistical profile of its traffic match their counterparts after embedding.

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The Computational Resiliency library (CRLib) provides distributed systems with the ability to sustain operation and dynamically restore the level of assurance in system function during attacks or failures. In the presence of arbitrary faults, replicated threads need to agree on the values received in order t o achieve consistency, when doing group communication in CRLib. To guarantee data integrity and increase reliability, we have implemented a variant of the Lamport-Shostak-Pease oral message algorithm for the Byzantine Generals problem, which provides fuzzy agreement as well as a reduction of the expected communication overhead. Instead of agreeing on the original messages, which could be extremely large, agreement is performed over the 160-bit hashes of normalized messages computed using SHA-1. Performance measurements of applications using CRLib supporting both fail-stop and arbitrary failure models indicate that a reasonable overhead in execution time is worth paying in cases when Byzantine failures are expected.