Watermarking-Based Digital Audio Data Authentication

EURASIP Journal on Applied Signal Processing 2003:10, 1001–1015 c 2003 Hindawi Publishing Corporation
Watermarking-Based Digital Audio Data Authentication Martin Steinebach Fraunhofer Institute IPSI, MERIT, C4M Competence for Media Security, D-64293 Darmstadt, Germany Email: Jana Dittmann Platanista GmbH and Otto-von-Guericke University Magdeburg, 39106 Magdeburg, Germany Email: Received 11 July 2002 and in revised form 4 January 2003 Digital watermarking has become an accepted technology for enabling multimedia protection schemes. While most efforts concentrate on user authentication, recently interest in data authentication to ensure data integrity has been increasing. Existing concepts address mainly image data. Depending on the necessary security level and the sensitivity to detect changes in the media, we differentiate between fragile, semifragile, and content-fragile watermarking approaches for media authentication. Furthermore, invertible watermarking schemes exist while each bit change can be recognized by the watermark which can be extracted and the original data can be reproduced for high-security applications. Later approaches can be extended with cryptographic approaches like digital signatures. As we see from the literature, only few audio approaches exist and the audio domain requires additional strategies for time flow protection and resynchronization. To allow different security levels, we have to identify relevant audio features that can be used to determine content manipulations. Furthermore, in the field of invertible schemes, there are a bunch of publications for image and video data but no approaches for digital audio to ensure data authentication for high-security applications. In this paper, we introduce and evaluate two watermarking algorithms for digital audio data, addressing content integrity protection. In our first approach, we discuss possible features for a content-fragile watermarking scheme to allow several postproduction modifications. The second approach is designed for high-security applications to detect each bit change and reconstruct the original audio by introducing an invertible audio watermarking concept. Based on the invertible audio scheme, we combine digital signature schemes and digital watermarking to provide a public verifiable data authentication and a reproduction of the original, protected with a secret key. Keywords and phrases: multimedia security, manipulation recognition, content-fragile watermarking, invertible watermarking, digital signature, original protection. 1. INTRODUCTION Multimedia data manipulation has become more and more simple and undetectable by the human audible and visual system due to technology advances in recent years. While this enables numerous new applications and generally makes it convenient to work with image, audio, or video data, a certain loss of trust in media data can be observed. As we see in Figure 1, small changes in the audio stream can cause a different meaning of the whole sentence. Regarding security particularly in the field of multimedia, the requirements on security increase. The possibility and the way of applying security mechanisms to multimedia data and their applications need to be analyzed for each purpose separately. This is mainly due to the structure and complexity of multimedia, see, for example, [1]. The security requirements such as integrity (unauthorized modification of data) or data authentication (detection of origin and data alterations) can be met by the succeeding security measures using cryptographic mechanisms and digital watermarking techniques [1]. Digital watermarking techniques based on steganographic systems embed information directly into the media data. Besides cryptographic mechanisms, watermarking represents an efficient technology to ensure both data integrity and data origin authenticity. Copyright, customer, or integrity information can be embedded, using a secret key, into the media data as transparent patterns. Based on the application areas for digital watermarking known today, the following five watermarking classes are defined: authentication watermarks, fingerprint watermarks, copy control watermarks, annotation watermarks, and integrity watermarks. The most important 1002 EURASIP Journal on Applied Signal Processing I am not guilty I am guilty Figure 1: Digital audio data is easily manipulated. properties of digital watermarking techniques are robustness, security, imperceptibility/transparency, complexity, capacity, and possibility of verification and invertibility, see, for example, [2]. Robustness describes whether the watermark can be reliably detected after media operations. It is important to note that robustness does not include attacks on the embedding schemes that are based on the knowledge of the embedding algorithm or on the availability of the detector function. Robustness means resistance to “blind,” nontargeted modifications, or common media operations. For example, the Stirmark tool [3] attacks the robustness of watermarking algorithms with geometrical distortions. For manipulation recognition, the watermark has to be fragile to detect altered media. Security describes whether the embedded watermarking information cannot be removed beyond reliable detection by targeted attacks based on full knowledge of the embedding and detection algorithm and possession of at least one watermarked data. Only the applied secret key remains unknown to the attacker. The concept of security includes procedural attacks or attacks based on a partial knowledge of the carrier modifications due to message embedding. The security aspect also includes the false positive detection rates. Transparency relates to the properties of the human sensory system. A transparent watermark causes no perceptible artifacts or quality loss. Complexity describes the effort and time we need to embed and retrieve a watermark. This parameter is essential for real-time applications. Another aspect addresses whether the original data is required in the retrieval process or not. We distinguish between nonblind and blind watermarking schemes, the latter require no original copy for detection. Capacity describes how many information bits can be embedded into the cover data. It also addresses the possibil- ity of embedding multiple watermarks in one document in parallel. The verification procedure distinguishes between private verification similar to symmetric cryptography and public verification like in asymmetric cryptography. Furthermore, during verification, we differ between invertible and noninvertible techniques, where the first one allows the reproduction of the original and the last one provides no possibility to extract the watermark without alterations of the original. The optimization of the parameters is mutually competitive and cannot be clearly done at the same time. If we want to embed a large message, we cannot require strong robustness sim (...truncated)