Protection of image and measurement data in an open network for traffic enforcement

Abstract

Efficient traffic enforcement requires measuring systems using digital cameras instead of wet film technology. The digital file containing the image data and the measured speed and/or other values are transferred to a central office without personnel at place. A type approval for such a system – as necessary in most countries – has to ensure the authenticity and integrity of these data with the goal of being accepted as evidence at court. The company Robot has developed a speed-measuring instrument using a digital camera system that has been type approved by PTB and is used by the German police since 2003. This paper firstly presents the technique of this system as an example to protect these data. The second part describes the in-depth validation method performed at PTB in the framework of the type approval procedure with the focus on the analysis of securing means of the operating system and of the applied cryptographic algorithms. The basis is a detailed and structured set of specifications and requirements that has been drafted by a consortium within the project VERA 2 funded by the EC.

Introduction

Digital imaging and networking technology are increasingly used in many fields, particularly for measurements in locations that are inconvenient to reach or even inaccessible for personnel. Continuous traffic enforcement in tunnels is a striking example. The bodies in charge as well as the manufacturers who develop measuring systems for traffic enforcement were aware of the advantages of the new technology compared to the established isolated local systems. Fig. 1, Fig. 2illustrate a digital imaging system that utilises the advantages of a digital camera and a network solution.

A sensor measuring the speed of the passing vehicles triggers a digital camera. The image data and the measured speed and some other data are combined to an event file that is compressed if necessary and then transferred to a central office via a network (ISDN or Ethernet). This transfer is protected by a digital signature and encryption. In the office the correctness of the signature must be checked before using the file for enforcement purposes (see Fig. 3).

Various obstacles had to be overcome before such a system could be implemented. In particular certain constraints in legal metrology have to be observed. In Germany and many other countries measuring instruments and their auxiliary devices used for traffic enforcement run through a two-step legal procedure. Firstly a pattern of the measuring system is examined and approved by a Notified Body with the result of a homologation. Secondly each batch-produced instrument is legally verified before put into use. Legal verification is repeated in fixed intervals.

Bodies in charge and manufacturers had to clarify how digital images and data transferred via networks could be sufficiently secured for the purpose of serving as an evidence. From the manufacturer's point of view development of such complex system only would be economically attractive, if this technology was accepted in many countries. As there is no EC directive harmonising traffic enforcement, authorities responsible for type approval and manufacturers from several European countries joined in two EC funded projects (VERA 1 and 2) for solving these problems. The authors of this article were instrumental in contributing to the result of these projects in developing a measuring system conform to the requirements defined, and in examining this measuring system.