Noise: an enemy to be dealt with and a major factor limiting communication system performance. However, what if there is gold in that garbage? In conventional engineering, our focus is primarily on eliminating, suppressing, combating, or even ignoring noise and its detrimental impacts. Conversely, could we exploit it similarly to biology, which utilizes noise-alike carrier signals to convey information? In this context, the utilization of noise, or noise-alike signals in general, has been put forward as a means to realize unconditionally secure communication systems in the future. In this tutorial article, we begin by tracing the origins of thermal noise-based communication and highlighting one of its significant applications for ensuring unconditionally secure networks: the Kirchhoff-law-Johnson-noise (KLJN) secure key exchange scheme. We then delve into the inherent challenges tied to secure communication and discuss the imperative need for physics-based key distribution schemes in pursuit of unconditional security. Concurrently, we provide a concise overview of quantum key distribution (QKD) schemes and draw comparisons with their KLJN-based counterparts. Finally, extending beyond wired communication loops, we explore the transmission of noise signals over-the-air and evaluate their potential for stealth and secure wireless communication systems.

翻译：噪声：一个需要应对的敌人，也是限制通信系统性能的主要因素。然而，这些"垃圾"中是否蕴藏着黄金？在传统工程中，我们主要致力于消除、抑制、对抗甚至忽视噪声及其有害影响。反之，我们能否像生物学那样利用噪声——利用类似噪声的载波信号来传递信息？在此背景下，利用噪声或一般意义上的类噪声信号，已被提出作为未来实现无条件安全通信系统的一种手段。在本教程文章中，我们首先追溯基于热噪声通信的起源，并重点介绍其确保无条件安全网络的一项重要应用：基尔霍夫定律-约翰逊噪声（KLJN）安全密钥交换方案。随后，我们深入探讨安全通信固有的挑战，并讨论在追求无条件安全过程中基于物理的密钥分发方案的必要性。同时，我们简要概述量子密钥分发（QKD）方案，并将其与基于KLJN的方案进行比较。最后，在有线通信环路之外，我们探索噪声信号在空中的传输，并评估其在隐身和安全无线通信系统中的潜力。