Information hiding for spatial and geographical data

Abstract

A geographical information system (GIS) represents geographical and spatial data through digital maps that are built according to a specific representation model. A digital map represents a set of features that are stored as couples < attribute, value > for each position in the map. These features may be organized into different layers in the map. Each layer logically represents a set of elementary features that can be used in a specific working activity, or they can be used in addition to other features belonging to other layers. Figure 11.1 illustrates the abstract representation of a GIS as a collection of different layers. In this example, the digital map is composed of four layers: a spatial coordinate system layer, a regions layer, a rivers layer, and a towns layer. All of them may be visualized together or separately. Also, features that belong to different layers may be selected by the user and some operations can be performed over them in order to obtain a new digital map. This is a distinguishing property of GIS. Thus, digital maps can be visualized according to GIS users' preferences, that is, GIS users may select some features to proceed with their working activity, or they can compose new layers starting from the ones that they have. For example, if a user is interested in visualizing the rivers, which go through the eastern towns, first, the user should select the features from the towns and rivers layers properly, and then the user should be able to create a new map that visualizes a new layer containing the rivers features that correspond to the user query. In recent years the development of communications in terms of technology and applications has influenced several domains in the public sector, including finance, marketing, arts, and administrative services. The main relevant events include the spreading of satellite and mobile communications. Consequently, Web-based applications are emerging to make information available to public and private clients. The technology evolution improves the cooperation between the public agencies and the efficiency of public and private services. However, while the technological advances help people to access public information and public services more easily, on the other hand, new problems about privacy and security arise. For example, a typical risk concerns the fact that the data could be captured by unauthorized users. Thus, 236 Maria Calagna and Luigi V. Mancini Fig. 11.1. A digital map is built upon a set of layers. Each layer logically represents a kind of information that can be used as it is or in conjunction with information belonging to other layers we need to make additional efforts in order to achieve the security and the protection requirements for the new emergent applications. Digital watermarking is a common solution that is used in order to realize the above requirements. It is classified as an information hiding technique, since it embeds a secret message, the watermark, in some valuable data in order to protect the intellectual property. In the GIS field, it is employed in order to address the problem of intellectual property protection, including copyright protection and fingerprinting of digital maps. The former concerns the protection of the owner digital rights on maps, while the latter can actually identify who is authorized to receive a digital map in a distributed GIS. Then, if the receivers try to circumvent the system policies, by re-distributing illegal digital maps to unauthorized entities, it is possible to identify who is the traitor. Section 11.3 describes the GIS application scenarios that can benefit from watermarking. A related information hiding technique is steganography that is used in order to conceal the secret message's very existence.We observe that steganography may be used with the aim to communicate secretly among authorized users. The authorized users may retrieve the hidden content, while unauthorized users are unable to detect that any hidden content is exchanged between the authorized entities. The addition of steganography to digital maps is more powerful than its application to other kind of representation, including, simple images, for example. In fact, according to the GIS description that was given above,many GIS operations are available to the users who are able to combine geographical and spatial data in several ways. Section 11.5 illustrates a possible application that integrates steganography with digital mapping. The chapter is structured as follows. Section 11.2 introduces the fundamentals of security and protection mechanisms, particularly concerning information hiding techniques. Further details on watermarking and steganography are given in Sects. 11.2.1 and 11.2.2, while Sect. 11.2.3 introduces the main properties of information hiding systems. The structure of the chapter continues with Sects. 11.3-11.4 and 11.5-11.6 introducing the watermarking and steganography techniques for spatial and geographical data, respectively. In particular, Sect. 11.4 illustrates a proposal for 11 Information Hiding for Spatial and Geographical Data 237 a watermarking scheme, developed within the SPADA@WEB project [27], that is based on the use of the SVD (singular value decomposition) transform by blocks, while Sect. 11.6 illustrates a proposal for a steganography GIS model that is based on the use of public keys with the aim to transmit sensitive content inside digital maps, making the hidden content available only to authorized users. © Springer-Verlag Berlin Heidelberg 2007. All rights are reserved.