# Satellite quantum communications when man-in-the-middle attacks are excluded

## TL;DR

This paper proposes simplified satellite quantum communication protocols called PKD, which, assuming man-in-the-middle attacks are detectable, achieve higher key rates than standard QKD by relaxing security assumptions.

## Contribution

It introduces photon key distribution (PKD) protocols for satellite quantum communications that improve key rates by simplifying hardware and security assumptions.

## Key findings

- PKD protocols have roughly twice the key rate of QKD.
- PKD can operate effectively at very high losses.
- Relaxed security assumptions enable higher efficiency.

## Abstract

An application of quantum communications is the transmission of qubits to create shared symmetric encryption keys in a process called Quantum Key Distribution (QKD). Contrary to public-private key encryption, symmetric encryption is safe from (quantum) computing attacks, i.e. it provides forward security and is thus attractive for secure communications. In this paper we argue that for free-space quantum communications, especially with satellites, if one assumes that man-in-the-middle attacks can be detected by classical channel monitoring techniques, simplified quantum communications protocols and hardware systems can be implemented that offer improved key rates. We term these protocols photon key distribution (PKD) to differentiate them from the standard QKD protocols. We identify three types of photon sources and calculate asymptotic secret key rates for PKD protocols and compare them to their QKD counterparts. Results show that PKD protocols have roughly a factor of two higher rates as only one measurement basis is used and due to the relaxed security assumptions can establish keys at very high losses whereas in QKD the privacy amplification process becomes prohibitive.