Mehmet Utku Celik

Lossless generalized-LSB data embedding

We present a novel lossless (reversible) data-embedding technique, which enables the exact recovery of the original host signal upon extraction of the embedded information. A generalization of the well-known least significant bit (LSB) modification is proposed as the data-embedding method, which introduces additional operating points on the capacity-distortion curve. Lossless recovery of the original is achieved by compressing portions of the signal that are susceptible to embedding distortion and transmitting these compressed descriptions as a part of the embedded payload. A prediction-based conditional entropy coder which utilizes unaltered portions of the host signal as side-information improves the compression efficiency and, thus, the lossless data-embedding capacity.

Reversible data hiding

We present a novel reversible (lossless) data hiding (embedding) technique, which enables the exact recovery of the original host signal upon extraction of the embedded information. A generalization of the well-known LSB (least significant bit) modification is proposed as the data embedding method, which introduces additional operating points on the capacity-distortion curve. Lossless recovery of the original is achieved by compressing portions of the signal that are susceptible to embedding distortion, and transmitting these compressed descriptions as a part of the embedded payload. A prediction-based conditional entropy coder which utilizes static portions of the host as side-information improves the compression efficiency, and thus the lossless data embedding capacity.

Lossless watermarking for image authentication: a new framework and an implementation

We present a novel framework for lossless (invertible) authentication watermarking, which enables zero-distortion reconstruction of the un-watermarked images upon verification. As opposed to earlier lossless authentication methods that required reconstruction of the original image prior to validation, the new framework allows validation of the watermarked images before recovery of the original image. This reduces computational requirements in situations when either the verification step fails or the zero-distortion reconstruction is not needed. For verified images, integrity of the reconstructed image is ensured by the uniqueness of the reconstruction procedure. The framework also enables public(-key) authentication without granting access to the perfect original and allows for efficient tamper localization. Effectiveness of the framework is demonstrated by implementing the framework using hierarchical image authentication along with lossless generalized-least significant bit data embedding.

Privacy preserving error resilient dna searching through oblivious automata

Human Desoxyribo-Nucleic Acid (DNA) sequences offer a wealth of information that reveal, among others, predisposition to various diseases and paternity relations. The breadth and personalized nature of this information highlights the need for privacy-preserving protocols. In this paper, we present a new error-resilient privacy-preserving string searching protocol that is suitable for running private DNA queries. This protocol checks if a short template (e.g., a string that describes a mutation leading to a disease), known to one party, is present inside a DNA sequence owned by another party, accounting for possible errors and without disclosing to each party the other partys input. Each query is formulated as a regular expression over a finite alphabet and implemented as an automaton. As the main technical contribution, we provide a protocol that allows to execute any finite state machine in an oblivious manner, requiring a communication complexity which is linear both in the number of states and the length of the input string.

Digital watermarking of low bit-rate advanced simple profile MPEG-4 compressed video

A novel MPEG-4 compressed domain video watermarking method is proposed and its performance is studied at video bit rates ranging from 128 to 768 kb/s. The spatial spread-spectrum watermark is embedded directly into compressed MPEG-4 bitstreams by modifying DCT coefficients. A synchronization template combats geometric attacks, such as cropping, scaling, and rotation. The method also features a gain control algorithm that adjusts the embedding strength of the watermark depending on local image characteristics, increasing watermark robustness or, equivalently, reducing the watermarks impact on visual quality. A drift compensator prevents the accumulation of watermark distortion and reduces watermark self-interference due to temporal prediction in inter-coded frames and AC/DC prediction in intra-coded frames. A bit-rate controller maintains the bit rate of the watermarked video within an acceptable limit. The watermark was evaluated and found to be robust against a variety of attacks, including transcoding, scaling, rotation, and noise reduction.

Secure watermark embedding through partial encryption

Secure watermark embedding allows to securely embed a watermark into a piece of content at an untrusted user device without compromising the security of the watermark key, the watermark or the original. In this paper, we show how secure embedding can be achieved by using traditional watermarking schemes in conjunction with partial encryption techniques, which were primarily developed to facilitate fast encryption of media content. Based on this concept, we develop two new efficient secure embedding mechanisms, one for the MASK watermarking scheme operating on baseband audio and one for a spread spectrum watermarking scheme operating on MPEG-2 encoded video streams.

A Buyer–Seller Watermarking Protocol Based on Secure Embedding

In a forensic watermarking architecture, a buyer-seller protocol protects the watermark secrets from the buyer and prevents false infringement accusations by the seller. Existing protocols encrypt the watermark and the content with a homomorphic public-key cipher and perform embedding under encryption. When used for multimedia data, these protocols create a large computation and bandwidth overhead. In this correspondence, we show that the same functionality can be achieved efficiently using recently proposed secure watermark embedding algorithms.

Lookup-Table-Based Secure Client-Side Embedding for Spread-Spectrum Watermarks

Today, mass-scale electronic content distribution systems embed forensic tracking watermarks primarily at the distribution server. For limiting the bandwidth usage and server complexity and enhancing scalability, it is preferable to embed the watermark at the client. Embedding in these untrusted clients requires secure embedding methods that do not leak unmarked content or the watermarking secrets. In this work, we propose a secure watermark embedding scheme based on lookup tables for spread-spectrum watermarks, which are robust to noise and can be detected without comparison to the original content. We also develop fast detection mechanisms that make the watermark detection feasible for tracking systems with a large number of clients. Our fast detection algorithm improves detection speed of existing methods by six orders of magnitude in a typical system with millions of clients.

Localized Lossless Authentication Watermark (LAW)

A novel framework is proposed for lossless authentication watermarking of images which allows authentication and recovery of original images without any distortions. This overcomes a significant limitation of traditional authentication watermarks that irreversibly alter image data in the process of watermarking and authenticate the watermarked image rather than the original. In particular, authenticity is verified before full reconstruction of the original image, whose integrity is inferred from the reversibility of the watermarking procedure. This reduces computational requirements in situations when either the verification step fails or the zero-distortion reconstruction is not required. A particular instantiation of the framework is implemented using a hierarchical authentication scheme and the lossless generalized-LSB data embedding mechanism. The resulting algorithm, called localized lossless authentication watermark (LAW), can localize tampered regions of the image; has a low embedding distortion, which can be removed entirely if necessary; and supports public/private key authentication and recovery options. The effectiveness of the framework and the instantiation is demonstrated through examples.

A secure multidimensional point inclusion protocol

Signal processing in the encrypted domain combines typical signal processing operations and cryptographic primitives to ensure security in applications involving mutually distrusting participants. Several such applications reduce to a multidimensional point inclusion problem where two participants decide whether a point known to the first lies inside a region specified by the second. In a secure solution, neither party gains knowledge about the others input. For instance, in biometric authentication the client can prove his identity without disclosing his biometric. In this paper, we present a new primitive for securely solving the multidimensional point inclusion problem. Using this primitive, we first propose an efficient and provably secure protocol that solves the problem for an N-dimensional convex region bounded with hyperplanes. We subsequently extend the protocol to inclusion in multiple hyperellipsoidal regions. Considering possible reduction strategies such as input packing, we analyze the complexity of both protocols.