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UBC Theses and Dissertations

Improved spread spectrum schemes for data hiding and their security analysis under known message attack Valizadeh, Amir


The massive production and easy use of digital media pose new challenges on protecting intellectual property of digital media. Digital data hiding, which can be defined as the procedure of embedding information into an original media host signal, is a promising technique for digital intellectual property protection. A data hiding system generally contains two major components: the encoder for embedding the hidden information and the decoder for extracting the hidden information. This thesis focuses on spread spectrum (SS) watermarking schemes for data hiding. Watermarking techniques for data hiding can be broadly categorized into two classes: quantization index modulation (QIM) based and spread spectrum based approaches. Being robust against distortions and having simple decoder structure make SS attractive for data hiding. First, we investigate the decoding performance of the traditional SS schemes in the DCT and DFT domains. To obtain more practical decoders, we propose using suboptimal decoders which do not need side information. Secondly, since the interference effect of the host signal causes decoding performance degradation in the additive SS scheme, to remove this host effect efficiently, we propose the correlation-and-bit-aware concept for data hiding by exploiting the side information at the encoder side and propose two improved SS-based schemes, the correlation-aware SS (CASS) and the correlation-aware improved SS (CAISS) embedding schemes. Thirdly, we analyze the decoding error probability and capacity of the multiplicative spread spectrum (MSS) embedding scheme, and show that the content-based MSS still suffers from the interference effect of the host signal. We then propose an improved MSS-based scheme by efficiently removing the host interference effect. Lastly, we present the security analysis of the SS-based data hiding schemes under the Known Message Attack (KMA) scenario. Each data hiding scheme has some secret parameters and here the security of a data hiding scheme represents the difficulty of estimating the secret parameters. We employ the mutual information between the observations and the secret parameters as a security measure. Also some practical estimators for estimating the signature code are introduced and their performances are reported to illustrate the security results.

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