Flow watermarks efficiently link packet flows in a network in order to thwart various attacks such as stepping stones. We study the problem of designing good flow watermarks. Earlier flow watermarking schemes mostly considered substitution errors, neglecting the effects of packet insertions and deletions that commonly happen within a network. More recent schemes consider packet deletions but often at the expense of the watermark visibility. We present an invisible flow watermarking scheme capable of enduring a large number of packet losses and insertions. To maintain invisibility, our scheme uses quantization index modulation (QIM) to embed the watermark into inter-packet delays, as opposed to time intervals including many packets. As the watermark is injected within individual packets, packet losses and insertions may lead to watermark desynchronization and substitution errors. To address this issue, we add a layer of error-correction coding to our scheme. Experimental results on both synthetic and real network traces demonstrate that our scheme is robust to network jitter, packet drops and splits, while remaining invisible to an attacker.
Earlier flow watermarks are of inter packet delay (IPD)-based type. @cite_23 , the authors propose an IPD-based scheme that modulates the mean of selected IPDs using the QIM framework. Watermark synchronization is lost if enough packets are dropped or split. Therefore the scheme is unreliable. Another IPD-based scheme is presented in @cite_25 , where watermarks are added by enlarging or shrinking the IPDs. This non-blind scheme achieves some watermark resynchronizations when packets are dropped or split, but is not scalable as the original packet flow is required during decoding.
@cite_25 @cite_23
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Network based intruders seldom attack directly from their own hosts, but rather stage their attacks through intermediate "stepping stones" to conceal their identity and origin. To identify attackers behind stepping stones, it is necessary to be able to correlate connections through stepping stones, even if those connections are encrypted or perturbed by the intruder to prevent traceability.The timing-based approach is the most capable and promising current method for correlating encrypted connections. However, previous timing-based approaches are vulnerable to packet timing perturbations introduced by the attacker at stepping stones. In this paper, we propose a novel watermark-based correlation scheme that is designed specifically to be robust against timing perturbations. The watermark is introduced by slightly adjusting the timing of selected packets of the flow. By utilizing redundancy techniques, we have developed a robust watermark correlation framework that reveals a rather surprising result on the inherent limits of independent and identically distributed (iid) random timing perturbations over sufficiently long flows. We also identify the tradeoffs between timing perturbation characteristics and achievable correlation effectiveness. Experiments show that the new method performs significantly better than existing, passive, timing-based correlation in the presence of random packet timing perturbations. In this paper, we present two watermarking approaches that are robust to geometric distortions. The first approach is based on image normalization, in which both watermark embedding and extraction are carried out with respect to an image normalized to meet a set of predefined moment criteria. We propose a new normalization procedure, which is invariant to affine transform attacks. The resulting watermarking scheme is suitable for public watermarking applications, where the original image is not available for watermark extraction. The second approach is based on a watermark resynchronization scheme aimed to alleviate the effects of random bending attacks. In this scheme, a deformable mesh is used to correct the distortion caused by the attack. The watermark is then extracted from the corrected image. In contrast to the first scheme, the latter is suitable for private watermarking applications, where the original image is necessary for watermark detection. In both schemes, we employ a direct-sequence code division multiple access approach to embed a multibit watermark in the discrete cosine transform domain of the image. Numerical experiments demonstrate that the proposed watermarking schemes are robust to a wide range of geometric attacks. Traditional watermarking schemes are sensitive to geometric distortions, in which synchronisation for recovering embedded information is a challenging task because of the disorder caused by rotation, scaling or translation (RST). The existing RST-resistant watermarking methods still have limitations with respect to robustness, capacity or fidelity. In this study, the authors address several major problems in RST-invariant watermarking. The first point is how to take advantage of the high RST resilience of scale-invariant feature transform (SIFT) features, which show good performance in terms of RST-resistant pattern recognition. Since many keypoint-based watermarking methods do not discuss cropping attacks, the second issue discussed in this study is how to resist cropping using a human visual system (HVS), which also helps us to eliminate computational complexity. The third issue is the investigation of an HVS-based watermarking strategy for extracting only feature points in the human attentive area. Lastly, a variable-length watermark synchronisation algorithm using dynamic programming is proposed. Experimental results show that the proposed algorithms are practical and show superior performance in comparison with many existing works in terms of watermark capacity, watermark transparency, and the resistance to RST attacks. A robust video watermarking scheme resilient to spatial desynchronization and photometric distortion is presented. The scheme is based on geometrically approximate invariant watermarking and adaptive watermarking, and it embeds watermark by modifying middle frequency component adaptively according to persistence of vision and Watson's DCT based visual model. Experimental results show that the proposed watermarking scheme is not only robust against spatial desynchronization and photometric distortion, but also robust against their combination. Furthermore, it can resist randomly frame inserting or frame dropping to some extent