In this paper, we introduce a randomized bit encoding scheme that can strengthen the privacy protection on RFID tags. This scheme is used together with the backward channel protection method proposed by Choi and Roh in [1], which serves to protect the unique identifier of an RFID tag from disclosure to close-range eavesdroppers. Choi and Roh's method faces the 'same-bit' problem, in which some bits of the unique identifier could be disclosed, thereby revealing critical information. Our proposed scheme alleviates the 'same-bit' problem to a negligible level. Furthermore, we propose an enhanced system model that can protect the unique tag identifier from disclosure not only against eavesdroppers, but against unauthorized interrogators as well. A metric based on entropy was defined and used to measure the amount of protection offered by the scheme. A method to construct an optimal randomized n-bit encoding scheme was also described. In addition, theoretical analysis and simulations were conducted, which show that the proposed encoding scheme provides significant improvement (achieving almost twice the entropy) over no encoding.
This paper investigates previous blind SS schemes which do not employ the host objects in the detection process, espe cially the Improved Spread Spectrum (ISS) scheme. It shows that these schemes result in a high false positive probability even in the absence of any attack. Furthermore, we present an Obscure SS (OSS) scheme which balances the detector blind ness and detector performance by exploiting some auxiliary data which are not harmful to the copyright. The main ad vantages of OSS over the previous blind SS schemes are: (1) it does not make any statistical assumption on the host ob ject, and (2) It achieves low false probabilities (positive and negative) just as in non-blind SS schemes.keywords: Non-blind watermarking; Obscure water marking; Blind watermarking.
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