Embedding information in physically generated random bit sequences while maintaining certified randomness

TL;DR

This paper investigates how information can be embedded into physically generated random bit sequences without compromising their certified randomness, proposing a cryptosystem and challenging current randomness definitions.

Contribution

It introduces a method to embed information in physical random sequences while maintaining their certified randomness and proposes a new cryptosystem based on this principle.

Findings

Embedded information ratio exceeds 0.01 in experiments

Proposed cryptosystem conceals communication content within random sequences

Results suggest a need to redefine practical classical and quantum randomness measures

Abstract

Ultrafast physical random bit generation at hundreds of Gb/s rates, with verified randomness, is a crucial ingredient in secure communication and have recently emerged using optics based physical systems. Here we examine the inverse problem and measure the ratio of information bits that can be systematically embedded in a random bit sequence without degrading its certified randomness. These ratios exceed 0.01 in experimentally obtained long random bit sequences. Based on these findings we propose a high-capacity private-key cryptosystem with a finite key length, where the existence as well as the content of the communication is concealed in the random sequence. Our results call for a rethinking of the current quantitative definition of practical classical randomness as well as the measure of randomness generated by quantum methods, which have to include bounds using the proposed inverse information embedding method.