An untraceable RFID authentication scheme allows a legitimate reader to authenticate a tag, and at the same time it assures the privacy of the tag against unauthorized tracing. In this paper, we revisit three elliptic-curve based untraceable RFID authentication protocols recently published and show they are not secure against active attacks and do not support the untraceability for tags. We also provide a new construction to solve such problems using the elliptic-curved based Schnorr signature technique. Our construction satisfies all requirements for RFID security and privacy including replay protection, impersonation resistance, untraceability, and forward privacy. It requires only two point scalar multiplications and two hash operations with two messages exchanges. Compared to previous works, our construction has better security and efficiency.

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In 2009, Tsai et al. proposed reversible image hiding scheme using linear prediction coding and histogram shifting. Tsai et al.'s scheme improved the hiding capacity of Ni et al.'s scheme by using the prediction coding and two histograms. However, Tsai et al.'s scheme has problems. In the prediction coding, the basic pixel is not used from embedding procedure. Many additional communication data are generated because two peak and zero point pairs are generated by each block. To solve the problems, this paper proposes a novel reversible data hiding scheme based on modulo operation and histogram shifting. In experimental results, the hiding capacity was increased by 28% than Tsai et al.'s scheme. However, the additional communication data was decreased by 71%.

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Wang et al. proposed a histogram shifting imitationbased reversible data hiding scheme in 2013. They used the peak points of image intensity-based segments, instead of utilizing the peak point of an histogram. Their scheme has the limitation of the embedding capacity due to the embedding method. In this paper, we propose an improved data hiding scheme using median edge detection (MED) and hexadecimal exploiting modification direction (EMD). In embedding procedure, a predicted image is generated by using MED. The secret data is embedded into the peak points in segments by using hexadecimal EMD. In experimental results, the embedding capacity of the proposed scheme is superior to that of Wang et al.