# Covert Secret Key Generation with an Active Warden

## TL;DR

This paper introduces an adaptive protocol for covert and secret key generation over state-dependent channels, ensuring communication remains undetectable from an active warden and partially characterizes the covert secret key capacity.

## Contribution

It proposes a novel adaptive protocol for covert secret key generation that works against active wardens and provides capacity characterization for passive adversaries.

## Key findings

- Protocol achieves covert secret key exchange with active wardens.
- Capacity equals covert capacity in some cases, enabling secret keys without additional cost.
- Partial characterization of covert secret key capacity for passive adversaries.

## Abstract

We investigate the problem of covert and secret key generation over a state-dependent discrete memoryless channel with one-way public discussion in which an adversary, the warden, may arbitrarily choose the channel state. We develop an adaptive protocol that, under conditions that we explicitly specify, not only allows the transmitter and the legitimate receiver to exchange a secret key but also conceals from the active warden whether the protocol is being run. When specialized to passive adversaries that do not control the channel state, we partially characterize the covert secret key capacity. In particular, the covert secret key capacity is sometimes equal to the covert capacity of the channel, so that secrecy comes "for free."