# Secret Key Capacity For Multipleaccess Channel With Public Feedback

## TL;DR

This paper investigates the maximum secret key rates achievable over a multipleaccess channel with public feedback, deriving bounds and proposing schemes that improve known rates, including for symmetric and adder MACs.

## Contribution

It establishes upper bounds on secret key capacity under different public communication restrictions and introduces a scheme that surpasses previous rates for symmetric MACs.

## Key findings

- Upper bounds on SK rates with feedback and no-feedback protocols.
- A new scheme achieving the maximum symmetric rate in symmetric MACs.
- Exact SK capacity for adder MAC without protocol restrictions.

## Abstract

We consider the generation of a secret key (SK) by the inputs and the output of a secure multipleaccess channel (MAC) that additionally have access to a noiseless public communication channel. Under specific restrictions on the protocols, we derive various upper bounds on the rate of such SKs. Specifically, if the public communication consists of only the feedback from the output terminal, then the rate of SKs that can be generated is bounded above by the maximum symmetric rate $R_f^\ast$ in the capacity region of the MAC with feedback. On the other hand, if the public communication is allowed only before and after the transmission over the MAC, then the rate of SKs is bounded above by the maximum symmetric rate $R^\ast$ in the capacity region of the MAC without feedback. Furthermore, for a symmetric MAC, we present a scheme that generates an SK of rate $R_f^\ast$, improving the best previously known achievable rate $R^\ast$. An application of our results establishes the SK capacity for adder MAC, without any restriction on the protocols.