Darko Kirovski

Spread-spectrum watermarking of audio signals

Watermarking has become a technology of choice for a broad range of multimedia copyright protection applications. Watermarks have also been used to embed format-independent metadata in audio/video signals in a way that is robust to common editing. In this paper, we present several novel mechanisms for effective encoding and detection of direct-sequence spread-spectrum watermarks in audio signals. The developed techniques aim at (i) improving detection convergence and robustness, (ii) improving watermark imperceptiveness, (iii) preventing desynchronization attacks, (iv) alleviating estimation/removal attacks, and finally, (v) establishing covert communication over a public audio channel. We explore the security implications of the developed mechanisms and review watermark robustness on a benchmark suite that includes a combination of audio processing primitives including: time- and frequency-scaling with wow-and-flutter, additive and multiplicative noise, resampling, requantization, noise reduction, and filtering.

Real-time classification of dance gestures from skeleton animation

We present a real-time gesture classification system for skeletal wireframe motion. Its key components include an angular representation of the skeleton designed for recognition robustness under noisy input, a cascaded correlation-based classifier for multivariate time-series data, and a distance metric based on dynamic time-warping to evaluate the difference in motion between an acquired gesture and an oracle for the matching gesture. While the first and last tools are generic in nature and could be applied to any gesture-matching scenario, the classifier is conceived based on the assumption that the input motion adheres to a known, canonical time-base: a musical beat. On a benchmark comprising 28 gesture classes, hundreds of gesture instances recorded using the XBOX Kinect platform and performed by dozens of subjects for each gesture class, our classifier has an average accuracy of 96:9%, for approximately 4-second skeletal motion recordings. This accuracy is remarkable given the input noise from the real-time depth sensor.

Robust spread-spectrum audio watermarking

We present several mechanisms that enable effective spread-spectrum audio watermarking systems: prevention against detection desynchronization, cepstrum filtering, and chess watermarks. We have incorporated these techniques into a system capable of reliably detecting a watermark in an audio clip that has been modified using a composition of attacks that degrade the original audio characteristics well beyond the limit of acceptable quality. Such attacks include: fluctuating scaling in the time and frequency domain, compression, addition and multiplication of noise, resampling, requantization, normalization, filtering, and random cutting and pasting of signal samples.

Power optimization of variable-voltage core-based systems

The growing class of portable systems, such as personal computing and communication devices, has resulted in a new set of system design requirements, mainly characterized by dominant importance of power minimization and design reuse. The energy efficiency of systems-on-a-chip (SOC) could be much improved if one were to vary the supply voltage dynamically at run time. We developed the design methodology for the low-power core-based real-time SOC based on dynamically variable voltage hardware. The key challenge is to develop effective scheduling techniques that treat voltage as a variable to be determined, in addition to the conventional task scheduling and allocation. Our synthesis technique also addresses the selection of the processor core and the determination of the instruction and data cache size and configuration so as to fully exploit dynamically variable voltage hardware, which results in significantly lower power consumption for a set of target applications than existing techniques. The highlight of the proposed approach is the nonpreemptive scheduling heuristic, which results in solutions very close to optimal ones for many test cases. The effectiveness of the approach is demonstrated on a variety of modern industrial strength multimedia and communication applications.

Enabling trusted software integrity

Preventing execution of unauthorized software on a given computer plays a pivotal role in system security. The key problem is that although a program at the beginning of its execution can be verified as authentic, while running, its execution flow can be redirected to externally injected malicious code using, for example, a buffer overflow exploit. Existing techniques address this problem by trying to detect the intrusion at run-time or by formally verifying that the software is not prone to a particular attack.We take a radically different approach to this problem. We aim at intrusion prevention as the core technology for enabling secure computing systems. Intrusion prevention systems force an adversary to solve a computationally hard task in order to create a binary that can be executed on a given machine. In this paper, we present an exemplary system--SPEF--a combination of architectural and compilation techniques that ensure software integrity at run-time. SPEF embeds encrypted, processor-specific constraints into each block of instructions at software installation time and then verifies their existence at run-time. Thus, the processor can execute only properly installed programs, which makes installation the only system gate that needs to be protected. We have designed a SPEF prototype based on the ARM instruction set and validated its impact on security and performance using the MediaBench suite of applications.

Multimedia content screening using a dual watermarking and fingerprinting system

We present a new dual watermarking and fingerprinting system, where initially all copies of a protected object are identically watermarked using a secret key, but individual detection keys are distinct. By knowing a detection key, an adversary cannot recreate the original content from the watermarked content. However, knowledge of any one detection key is sufficient for modifying the object so that a detector using that key would fail to detect the marks. Detectors using other detection keys would not be fooled, and such a modified object necessarily contains enough information about the broken detector key - the fingerprint. Our dual system limits the scope of possible attacks, when compared to classic fingerprinting systems. Under optimal attacks, the size of the collusion necessary to remove the marks without leaving a detectable fingerprint is superlinear in object size, whereas classic fingerprinting has a lower bound on collusion resistance that is approximately fourth root in object size. By using our scheme one can achieve collusion resistance of up to 900,000 users for a two hour high-definition video.

Blind pattern matching attack on watermarking systems

Billions of dollars allegedly lost to piracy of multimedia content have triggered the industry to rethink the way music and films are distributed on the Internet. As encryption is vulnerable to digital or analog re-recording, currently almost all copyright protection mechanisms rely to a certain extent on watermarking. A watermark is an imperceptive secret hidden into a host signal. We analyze the security of multimedia copyright protection systems that use watermarks by proposing a new breed of attacks on generic watermarking systems. A typical blind pattern matching attack relies on the observation that multimedia content is often highly repetitive. Thus, the attack procedure identifies subsets of signal blocks that are similar and permutes these blocks. Assuming the permuted blocks are marked with distinct secrets, it can be shown that any watermark detector is facing a task of exponential complexity to reverse the permutations as a preprocessing step for watermark detection. We describe the logistics of the attack and an implementation against a spread-spectrum and a quantization index modulation data hiding technology for audio signals.

Detecting and tolerating asymmetric races

This paper introduces ToleRace, a runtime system that allows programs to detect and even tolerate asymmetric data races. Asymmetric races are race conditions where one thread correctly acquires and releases a lock for a shared variable while another thread improperly accesses the same variable. ToleRace provides approximate isolation in the critical sections of lock-based parallel programs by creating a local copy of each shared variable when entering a critical section, operating on the local copies, and propagating the appropriate copies upon leaving the critical section. We start by characterizing all possible interleavings that can cause races and precisely describe the effect of ToleRace in each case. Then, we study the theoretical aspects of an oracle that knows exactly what type of interleaving has occurred. Finally, we present two software implementations of ToleRace and evaluate them on multithreaded applications from the SPLASH2 and PARSEC suites. Our implementation on top of a dynamic instrumentation tool, which works directly on executables and requires no source code modifications, incurs an overhead of a factor of two on average. Manually adding ToleRace to the source code of these applications results in an average overhead of 6.4 percent.

On the feasibility of completely wireless datacenters

Conventional datacenters, based on wired networks, entail high wiring costs, suffer from performance bottlenecks, and have low resilience to network failures. In this paper, we investigate a radically new methodology for building wire-free datacenters based on emerging 60GHz RF technology. We propose a novel rack design and a resulting network topology inspired by Cayley graphs that provide a dense interconnect. Our exploration of the resulting design space shows that wireless datacenters built with this methodology can potentially attain higher aggregate bandwidth, lower latency, and substantially higher fault tolerance than a conventional wired datacenter while improving ease of construction and maintenance.

Digital rights management for digital cinema

There is a wide consensus among the feature film production studios that the Internet era brings a new paradigm for film distribution to cinemas worldwide. The benefits of digital cinema to both producers and cinemas are numerous: significantly lower distribution and maintenance costs, immediate access to film libraries, higher presentation quality, and strong potential for developing new business models. Despite these advantages, the studios are still reluctant to jump into the digital age. The main showstopper for digital cinema is the danger of widespread piracy. Piracy already costs Hollywood an estimated two billion dollars annually and digital cinema without proper copyright enforcement could increase this number. In this paper, we present a copyright management system that aims at providing the set of necessary security tools: standard cryptographic primitives and copyright protection mechanisms that enable a reliable and secure feature film delivery system.