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，如果这些“垃圾”中蕴藏着黄金呢？在传统工程中，我们的重点主要在于消除、抑制、对抗甚至忽略噪声及其有害影响。相反，我们能否像生物学那样利用它——生物学利用类噪声载波信号来传递信息？在此背景下，利用噪声或广义的类噪声信号，已被提出作为实现未来无条件安全通信系统的一种手段。在本篇综述文章中，我们首先追溯基于热噪声的通信起源，并强调其在确保无条件安全网络方面的一项重要应用：基尔霍夫定律-约翰逊噪声（KLJN）安全密钥交换方案。接着，我们深入探讨与安全通信相关的固有挑战，并讨论为实现无条件安全而对基于物理学的密钥分发方案的迫切需求。同时，我们简要概述量子密钥分发（QKD）方案，并与基于KLJN的方案进行比较。最后，我们将视野扩展到有线通信环路之外，探讨噪声信号的空中传输，并评估其在隐蔽和安全无线通信系统方面的潜力。