This paper proposes a new privacy-enhancing, context-aware user authentication system, ConSec, which uses a transformation of general location-sensitive data, such as GPS location, barometric altitude and noise levels, collected from the user's device, into a representation based on locality-sensitive hashing (LSH). The resulting hashes provide a dimensionality reduction of the underlying data, which we leverage to model users' behaviour for authentication using machine learning. We present how ConSec supports learning from categorical and numerical data, while addressing a number of on-device and network-based threats. ConSec is implemented subsequently for the Android platform and evaluated using data collected from 35 users, which is followed by a security and privacy analysis. We demonstrate that LSH presents a useful approach for context authentication from location-sensitive data without directly utilising plain measurements.

Billions of dollars allegedly lost to piracy of multimedia have recently triggered the industry to rethink the way music and movies are distributed. As encryption is vulnerable to rerecording, currently all copyright protection mechanisms tend to rely on watermarking. A watermark is an imperceptive secret hidden in a host signal. In this paper, 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 replacement attack relies upon the observation that multimedia content is often highly repetitive. Thus, the attack procedure replaces each signal block with another, perceptually similar block computed as a combination of other similar blocks found either within the same media clip or within a library of media clips. Assuming the blocks used to compute the replacement are marked with distinct secrets, we show that if the computed replacement block is at some minimal distance from the original marked block, a large portion of the embedded watermark is removed. We describe the logistics of the attack and an exemplary implementation against a spread-spectrum data hiding technology for audio signals.

Billions of dollars allegedly lost to piracy of multimedia content have recently triggered the industry to rethink the way how music and movies are distributed on the Internet. As encryption is vulnerable to digital or analog re-recording, currently almost all copyright protection mechanisms rely to certain extent on watermarking, i.e. hiding of imperceptive secrets into a host signal. In this paper, we propose a new breed of attacks on generic watermarking systems, which recognizes that multimedia content is often highly repetitive, identifies subsets of signal blocks that are similar, and finally permutes these blocks. Assuming the permuted blocks have been 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. In this paper, we describe the logistics of the attack and a recipe for its implementation against an audio watermarking technology.

Information-hiding techniques have recently become important in a number of application areas. Digital audio, video, and pictures are increasingly furnished with distinguishing but imperceptible marks, which may contain a hidden copyright notice or serial number or even help to prevent unauthorized copying directly. Military communications systems make increasing use of traffic security techniques which, rather than merely concealing the content of a message using encryption, seek to conceal its sender, its receiver, or its very existence. Similar techniques are used in some mobile phone systems and schemes proposed for digital elections. Criminals try to use whatever traffic security properties are provided intentionally or otherwise in the available communications systems, and police forces try to restrict their use. However, many of the techniques proposed in this young and rapidly evolving field can trace their history back to antiquity, and many of them are surprisingly easy to circumvent. In this article, we try to give an overview of the field, of what we know, what works, what does not, and what are the interesting topics for research.

In this paper, we clarify what steganography is and what it can do. We contrast it with the related disciplines of cryptography and traffic security, present a unified terminology agreed at the first international workshop on the subject, and outline a number of approaches-many of them developed to hide encrypted copyright marks or serial numbers in digital audio or video. We then present a number of attacks, some new, on such information hiding schemes. This leads to a discussion of the formidable obstacles that lie in the way of a general theory of information hiding systems (in the sense that Shannon gave us a general theory of secrecy systems). However, theoretical considerations lead to ideas of practical value, such as the use of parity checks to amplify covertness and provide public key steganography. Finally, we show that public key information hiding systems exist, and are not necessarily constrained to the case where the warden is passive.