# On-The-Fly Secure Key Generation with Deterministic Models

## TL;DR

This paper introduces an analytical framework for on-the-fly wireless secret key generation using unknown pilots and deterministic models, addressing limitations of traditional methods in low-mobility environments.

## Contribution

It develops a novel approximation model inspired by deterministic models to analyze and derive achievable key rates for on-the-fly key generation schemes.

## Key findings

- Derived achievable key rates in Alice-Bob-Eve setting.
- Introduced a new approximation model for analysis.
- Provided insights into performance bounds of the scheme.

## Abstract

It is well-known that wireless channel reciprocity together with fading can be exploited to generate a common secret key between two legitimate communication partners. This can be achieved by exchanging known deterministic pilot signals between both partners from which the random fading gains can be estimated and processed. However, the entropy and thus quality of the generated key depends on the channel coherence time. This can result in poor key generation rates in a low mobility environment, where the fading gains are nearly constant. Therefore, wide-spread deployment of wireless channel-based secret key generation is limited. To overcome these issues, we follow up on a recent idea which uses unknown random pilots and enables "on-the-fly" key generation. In addition, the scheme is able to incorporate local sources of randomness but performance bounds are hard to obtain with standard methods. In this paper, we analyse such a scheme analytically and derive achievable key rates in the Alice-Bob-Eve setting. For this purpose, we develop a novel approximation model which is inspired by the linear deterministic and the lower triangular deterministic model. Using this model, we can derive key rates for specific scenarios. We claim that our novel approach provides an intuitive and clear framework to analyse similar key generation problems.