Random number generation & distribution out of thin (or thick) air

TL;DR

This paper introduces a simple free-space scheme for generating and securely distributing random numbers using atmospheric turbulence, demonstrating practical implementation and potential security benefits against eavesdropping.

Contribution

A novel hybrid free-space link scheme utilizing atmospheric turbulence for both random number generation and secure distribution, with experimental validation and security analysis.

Findings

Achieved 84% fidelity in shared random bits between parties.

Eavesdropper's key fidelity is only 54%, close to the theoretical minimum.

Experimental results align well with turbulence statistics literature.

Abstract

Much scientific work has focused on the generation of random numbers as well as the distribution of said random numbers for use as a cryptographic key. However, emphasis is often placed on one of the two to the exclusion of the other, but both are often simultaneously important. Here we present a simple hybrid free-space link scheme for both the generation and secure distribution of (pseudo-)random numbers between two remote parties, drawing the randomness from the stochastic nature of atmospheric turbulence. The atmosphere is simulated using digital micro-mirror devices for efficient, all-digital control. After outlining one potential algorithm for extracting random numbers based on finding the centre-of-mass (COM) of turbulent beam intensity profiles, the statistics of our experimental COM measurements is studied and found to agree well with the literature. After implementing the scheme in the laboratory, Alice and Bob are able to establish a string of correlated random bits with an 84% fidelity. Finally, we make a simple modification to the original setup in an attempt to thwart the hacking attempts of an eavesdropper, Eve, who has access to the free-space portion of the link. We find that the fidelity between Eve's key and that of Alice/Bob is 54%, only slightly above the theoretical minimum. Atmospheric turbulence could hence be leveraged as an added security measure, rather than being seen as a drawback.