Electromagnetic noise as entropy source for cryptographic system

Abstract

This paper presents a system for gathering electromagnetic noise to extract surrounding entropy at 430 MHz. The uniqueness of electromagnetic noise depends on geographical location, time, used technology, and a plethora of other variables. The proposed system consisting of telescopic whip antenna and software defined radio HackRF One takes advantage of the said fact to extract entropy and transform it into a random number which could be then used in cryptography. Said system is supposed to be low-cost and made from generally available equipment to ensure usability for the general population. Three experiments were devised to transform received noise into random numbers. The first experiment extracts entropy from the time domain by averaging the magnitude of the signal and comparing it to magnitude. The second experiment uses Fast Fourier Transformation to obtain the frequency composition of the received signal and extracts entropy out of magnitude of different frequencies. The last experiment combines the two through logical operation XOR to gain the random number. Obtained random numbers are then tested for randomness by checking entropy, monobit test from NIST standard, and proportion of logic ones and zeroes in the sequence.