An invisible flow watermarking QIM scheme based on linear errorcorrecting subcodes for channels with substitution and deletion errors is proposed in this paper. The evaluation of scheme demonstrates similar to known scheme performance but with lower complexity as soon as its implementation is mainly based on linear decoding operations. Recently, an active approach of traffic analysis called "flow watermarking" has been considered. This approach attempts to manipulate the statistical properties of packets flow to insert a watermark making it easier to detect the flow after passing through one or more relay hosts. To prevent an attacker to tolerate the packet delays and to eliminate embedded watermark, recent schemes have concentrated on making them "invisible". This technique has been the subject of increased interest in the past decade, because it requires low computational and communication cost while providing high accuracy in linking traffic flows. Flow watermarking is also classified as interval-based and inter-packet-delay (IPD)-based. The first type of watermarking technique is robust to packet losses but is vulnerable to the multi-flow attack [1] . The IPD-based flow watermarking, in which the watermarks are embedded into the time intervals between arrivals of packets, resists this attack [2] . The drawback of this scheme is that it can cause a lot of errors in decoding during the loss of packet synchronization in the watermark detection process. A novel IPD-based flow watermarking scheme that can withstand packet losses has been done in [2] . In this scheme the watermark embedding has been done with the use of quantization index modulation (QIM) [3] . In this approach the embedded marks are invisible. To withstand packet losses authors develop a Hidden-Markov Model (HMM) decoding scheme considering the communication channel with dependent deletion and substitution errors. However, the proposed watermark detector based on a maximum likelihood decoding algorithm paired with a forwardbackward is of high complexity and requires a lot of computational resources. In this paper we propose the alternative IPD-flow watermarking QIM scheme, based on the use of linear error-correcting codes and Varshamov-Tenengol'ts (VT) codes [4] to reduce the complexity of flow watermarking method [2] .
An alternative scheme using linear error-correcting codes and VarshamovTenengol'ts (VT) codes was then proposed to further reduce the complexity of watermarking decoding REF .
Use of Linear Error-Correcting Subcodes in Flow Watermarking for Channels with Substitution and Deletion Errors
Communications and Multimedia Security
Computer Science