The detection of covert timing channels is of increasing interest in light of recent practice on the exploitation of covert timing channels over the Internet. However, due to the high variation in legitimate network traffic, detecting covert timing channels is a challenging task. The existing detection schemes are ineffective to detect most of the covert timing channels known to the security community. In this paper, we introduce a new entropy-based approach to detecting various covert timing channels. Our new approach is based on the observation that the creation of a covert timing channel has certain effects on the entropy of the original process, and hence, a change in the entropy of a process provides a critical clue for covert timing channel detection. Exploiting this observation, we investigate the use of entropy and conditional entropy in detecting covert timing channels. Our experimental results show that our entropy-based approach is sensitive to the current covert timing channels, and is capable of detecting them in an accurate manner.

Many users face surveillance of their Internet communications and a significant fraction suffer from outright blocking of certain destinations. Anonymous communication systems allow users to conceal the destinations they communicate with, but do not hide the fact that the users are using them. The mere use of such systems may invite suspicion, or access to them may be blocked. We therefore propose Cirripede, a system that can be used for unobservable communication with Internet destinations. Cirripede is designed to be deployed by ISPs; it interceptsconnectionsfromclientstoinnocent-lookingdestinations and redirects them to the true destination requested by the client. The communication is encoded in a way that is indistinguishable from normal communications to anyone without the master secret key, while public-key cryptography is used to eliminate the need for any secret information that must be shared with Cirripede users. Cirripede is designed to work scalably with routers that handle large volumes of traffic while imposing minimal overhead on ISPs and not disrupting existing traffic. This allows Cirripede proxies to be strategically deployed at central locations, making access to Cirripede very difficult to block. Webuiltaproof-of-conceptimplementationofCirripedeand performed a testbed evaluation of its performance properties.

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Abstract: Covert channel attacks utilise shared resources to indirectly transmit sensitive information to unauthorised parties. Current operating systems (e.g. SELinux) rely on tagging the filesystem with security labels and enforcing security policies at the time of access to a file or resource. However, such mechanisms do not provide strong protection against information laundering via covert channels. Colored Linux, an extension to SELinux, utilises watermarking algorithms to ‘colour ’ the contents of each file with their respective security classification, or context, to enhance resistance to information laundering attacks. In this study, the authors propose a mobile agent-based approach to automate the process of detecting and colouring receptive hosts’ filesystems and monitoring the coloured filesystem for instances of potential information leakage. Implementation details and execution results are included to illustrate the merits of the proposed approach. The authors have also evaluated the performance of their agent-based system over a single host as well as a local network of machines. Finally, using formal method techniques, the authors have proved correctness properties about the agent-based approach and identified and corrected a flaw in their initial implementation. 1

This paper describes steganographic timing channels that use cryptographic primitives to hide the presence of covert channels in the timing of network traffic. We have identified two key properties for steganographic timing channels: (1) the parameters of the scheme should be cryptographically keyed, and (2) the distribution of input timings should be indistinguishable from output timings. These properties are necessary (although we make no claim they are sufficient) for the undetectability of a steganographic timing channel. Without them, the contents of the channel can be read and observed by unauthorized persons, and the presence of the channel is trivially exposed by noticing large changes in timing distributions – a previously proposed methodology for covert channel detection. Our steganographic timing scheme meets the secrecy requirement by employing cryptographic keys, and we achieve a restricted form of input/output distribution parity. Under certain distributions, our schemes conforms to a uniformness property; input timings that are uniformly distributed modulo a timing window are indistinguishable from output timings, measured under the same modulo. We also demonstrate that our scheme is practical under real network conditions, and finally present an empirical study of its covertness using the firstorder entropy metric, as suggested by Gianvecchio and Wang [8], which is currently the best published practical detection heuristic for timing channels. 1