Digital Watermarking for Verification of Perception-based Integrity of Audio Data

In certain application fields digital audio recordings contain sensitive content. Examples are historical archival material in public archives that preserve our cultural heritage, or digital evidence in the context of law enforcement and civil proceedings. Because of the powerful capabilities of modern editing tools for multimedia such material is vulnerable to doctoring of the content and forgery of its origin with malicious intent. Also inadvertent data modification and mistaken origin can be caused by human error. Hence, the credibility and provenience in terms of an unadulterated and genuine state of such audio content and the confidence about its origin are critical factors. To address this issue, this PhD thesis proposes a mechanism for verifying the integrity and authenticity of digital sound recordings. It is designed and implemented to be insensitive to common post-processing operations of the audio data that influence the subjective acoustic perception only marginally (if at all). Examples of such operations include lossy compression that maintains a high sound quality of the audio media, or lossless format conversions. It is the objective to avoid de facto false alarms that would be expectedly observable in standard crypto-based authentication protocols in the presence of these legitimate post-processing. For achieving this, a feasible combination of the techniques of digital watermarking and audio-specific hashing is investigated. At first, a suitable secret-key dependent audio hashing algorithm is developed. It incorporates and enhances so-called audio fingerprinting technology from the state of the art in contentbased audio identification. The presented algorithm (denoted as ”rMAC” message authentication code) allows ”perception-based” verification of integrity. This means classifying integrity breaches as such not before they become audible. As another objective, this rMAC is embedded and stored silently inside the audio media by means of audio watermarking technology. This approach allows maintaining the authentication code across the above-mentioned admissible post-processing operations and making it available for integrity verification at a later date. For this, an existent secret-key ependent audio watermarking algorithm is used and enhanced in this thesis work. To some extent, the dependency of the rMAC and of the watermarking processing from a secret key also allows authenticating the origin of a protected audio. To elaborate on this security aspect, this work also estimates the brute-force efforts of an adversary attacking this combined rMAC-watermarking approach. The experimental results show that the proposed method provides a good distinction and classification performance of authentic versus doctored audio content. It also allows the temporal localization of audible data modification within a protected audio file. The experimental evaluation finally provides recommendations about technical configuration settings of the combined watermarking-hashing approach. Beyond the main topic of perception-based data integrity and data authenticity for audio, this PhD work provides new general findings in the fields of audio fingerprinting and digital watermarking. The main contributions of this PhD were published and presented mainly at conferences about multimedia security. These publications were cited by a number of other authors and hence had some impact on their works

Watermark-Based Authentication and Key Exchange in Teleconferencing Systems

Abstract. In this paper we propose an architecture which combines watermarking with traditional cryptographic key agreement protocols to establish an authenticated or encrypted channel in teleconferencing systems. Technically the proposed method embeds messages of the key agreement protocol within an audio or video stream and is based on the assumption that the human communication partners can recognize each other easily; the watermark establishes a close coupling between the cryptographic key exchange messages and the media stream. We argue that the security of the scheme is based on a yet unexplored security property of digital watermarks; furthermore we present preliminary research results that suggest that this property holds in standard watermarking schemes

Perception-based Audio Authentication Watermarking in the Time-Frequency Domain

Current systems and protocols based on cryptographic methods for integrity and authenticity verification of media data do not distinguish between legitimate signal transformation and malicious tampering that manipulates the content. Furthermore, they usually provide no localization or assessment of the relevance of such manipulations with respect to human perception or semantics. We present air algorithm for a authentication audio watermarking that uses a perception-based robust hash function in combination with robust watermarking to verify the integrity of audio recordings. Experimental results show that the proposed system provides both a high level of distinction between perceptually different audio data and a high robustness against signal transformations that do not change the perceived information

Data-Leakage-Tracking durch digitale Wasserzeichen

Datenlecks sind immer noch eine der größten Herausforderungen für Unternehmen, Behörden und sonstige Organisationen. Der vorliegende Beitrag präsentiert ein alternatives Lösungskonzept, um mittels digitaler Wasserzeichen im Fall des Falles Sicherheits- oder Datenschutzbrüche nachvollziehen und aufklären zu können