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The Sources of Randomness in Smartphones with Symbian OS

This paper is focused on the analysis of randomness sources available in current mobile phones. We discuss specifics of the mobile devices, identify potential sources of randomness, and define types of possible attackers. An analysis of a camera and a microphone input noise as a source of randomness has been performed and amount of available entropy estimated. We then also statistically tested the obtained data using NIST test battery. Preliminary version of entropy extraction function was implemented using cryptographic hash function and its performance tested on several mobile phones. This paper deals with issues related to the generation of truly random data (i.e., bits, numbers, and sequences) in mobile computing environments. We will describe the expected application requirements in terms of amount and speed of random data generation in such environments, and then we will focus on available sources of randomness in mobile devices with the Symbian OS. The main goal of this work is identification of such sources, evaluation of their acquisition speed, statistical testing of their quality, and estimation of the amount of available entropy in a given time period. Some issues described in this paper were partially discussed in Czech article (1). Our work will cover the possibilities of random data generation from both external and internal environmental characteristics. The examined external sources will be audio and video streams that can be captured using a mobile device. Additional external sources of location-based information like actual strength of the network signal or fluctuation in current GPS position will also be examined. With respect to the internal sources, we will investigate the information accessible through the application programming interfaces of the Symbian OS like the actual battery charge level and other accessible system statistics. All identified sources of randomness are tested on the Nokia N73 smartphone with respect to performance and statistical quality of the output. The performance tests should reveal a practical usability of particular sources of randomness for the concrete applications. Statistical testing of randomness should then reveal whether the output sequences does not suffer from known statistical defects and have appropriate statistical properties. We expect that entropy extraction or at least digital post-processing techniques will be necessary to gather a good quality (and unpredictable) truly random data, as some of the generators may produce a large amount of data with only a small amount of entropy.