Z. Jane Wang

Group-oriented fingerprinting for multimedia forensics

Digital fingerprinting of multimedia data involves embedding information in the content signal and offers protection to the digital rights of the content by allowing illegitimate usage of the content to be identified by authorized parties. One potential threat to fingerprinting is collusion, whereby a group of adversaries combine their individual copies in an attempt to remove the underlying fingerprints. Former studies indicate that collusion attacks based on a few dozen independent copies can confound a fingerprinting system that employs orthogonal modulation. However, in practice an adversary is more likely to collude with some users than with other users due to geographic or social circumstances. To take advantage of prior knowledge of the collusion pattern, we propose a two-tier group-oriented fingerprinting scheme where users likely to collude with each other are assigned correlated fingerprints. Additionally, we extend our construction to represent the natural social and geographic hierarchical relationships between users by developing a more flexible tree-structure-based fingerprinting system. We also propose a multistage colluder identification scheme by taking advantage of the hierarchial nature of the fingerprints. We evaluate the performance of the proposed fingerprinting scheme by studying the collusion resistance of a fingerprinting system employing Gaussian-distributed fingerprints. Our results show that the group-oriented fingerprinting system provides the superior collusion resistance over a system employing orthogonal modulation when knowledge of the potential collusion pattern is available.

Block-Level Unitary Query: Enabling Orthogonal-Like Space-Time Code With Query Diversity for MIMO Backscatter RFID

Future backscatter RFID systems are required to be more reliable and data intensive for emerging fields such as Internet of Things (IoT). Motivated by this, orthogonal space-time block code (OSTBC), which is very successful in mobile communications for its low complexity and high performance, has already been investigated for MIMO backscatter RFID. Also a recently proposed scheme called unitary query was shown to be able to considerably improve the reliability of MIMO backscatter RFID by exploiting query diversity. Therefore, incorporating the classical OSTBC (at the tag end) with the unitary query (at the query end) seems promising. However, in this paper, we first show that simple direct employment of OSTBC together with unitary query incurs a linear decoding problem and eventually leads to severe performance degradation. As a redesign of the unitary query idea and the classical OSTBC specifically for MIMO backscatter RFID, we present a BUTQ-mOSTBC design pair idea by proposing the block-level unitary query (BUTQ) at the query end and the corresponding modified OSTBC (mOSTBC) at the tag end. The proposed BUTQ-mOSTBC can resolve the linear decoding problem, keep the simplicity and high performance properties of the classical OSTBC, and achieve the query diversity for the MIMO backscatter RFID.

Unitary Query for the

A multiple-input multiple-output backscatter radio frequency identification (RFID) system consists of three operational ends: the query end (with M reader transmitting antennas), the tag end (with L tag antennas), and the receiving end (with N reader receiving antennas). Such an M × L × N setting in RFID can bring spatial diversity and has been studied with the use of space-time code (STC) at the tag end. Current research generally has ignored query signaling as a means to improve performance. Here we propose a novel unitary query scheme, which creates time diversity within the channel coherent time and can yield significant performance improvements. To overcome the difficulty of evaluating the performance when unitary query is employed at the query end and STC is employed at the tag end, we derive a new measure based on the ranks of certain carefully constructed matrices to show that unitary query has superior performance. Simulations show that unitary query can bring 5-10 dB gain in mid signal-to-noise ratio regimes. In addition, different from the conventional uniform query case, unitary query can also improve the performance of single-antenna tags significantly, enabling single-antenna tags with low complexity and small size to be used for high performance.

M\times L\times N

Digital fingerprints are unique labels inserted in different copies of the same content before distribution. Each digital fingerprint is assigned to an inteded recipient, and can be used to trace the culprits who use their content for unintended purposes. Attacks mounted by multiple users, known as collusion attacks, provide a cost-effective method for attenuating the identifying fingerprint from each coluder, thus collusion poses a reeal challenge to protect the digital media data and enforce usage policies. This paper examines a few major design methodologies for collusion-resistant fingerprinting of multimedia, and presents a unified framework that helps highlight the common issues and the uniqueness of different fingerprinting techniques.