The growth of data-driven technologies, 5G, and the Internet pose enormous pressure on underlying information infrastructure. There are numerous proposals on how to deal with the possible capacity crunch [1]. However, the security of both optical and wireless networks lags behind reliable and spectrally efficient transmission [2]. Significant achievements have been recently made in the arenas of quantum computing [3] and quantum communication [4, 5]. Because most conventional cryptography systems rely on computational security, which guarantees security against an efficient eavesdropper for a limited time, with advancements in quantum computing, this security can be compromised. To solve for these problems, various schemes providing the perfect/unconditional security have been proposed, including physical-layer security (PLS), quantum key distribution (QKD), and post-quantum cryptography. Unfortunately, it is still unclear how to integrate those different proposals with higher-level cryptography schemes. Thus, the purpose of this Special Issue was to integrate these various approaches and enable the next generation of cryptography systems whose security cannot be broken by quantum computers. The topics addressed in this Special Issue include physical-layer security [2], quantum key distribution (QKD) [2], post-quantum cryptography [6], quantum-enhanced cryptography [7], stealth communication [2], and covert communication [8]. There are 14 papers published in this Special Issue, distributed as follows: 1 review paper, 1 perspective paper, and 12 articles. In the review paper [9], authors apply the restricted Eve's concept to the satellite-to-satellite secret key distillation. In conventional QKD, it is assumed that [PERSON] is the omnipotent, limited only by the laws of physics. This represents an unreasonable assumption for certain applications, where the presence of [PERSON] is easy to detect, such as free-space optical communications, particularly satellite-to-satellite communications. By introducing geometrical optics within a restricted model, authors have shown that the secret key rate (SKR) can be significantly improved compared to the conventional QKD. Authors analyze SKRs from [PERSON]'s perspective through the exclusion zone approach and from [PERSON]'s perspective through dynamic positioning of the receiver aperture. In the perspective paper [10], the author discusses how to build a global quantum communication network (QCN) by interconnecting the disconnected terrestrial QCNs through LEO satellite QCN, based on the cluster state concept. This heterogenous global QCN will provide unprecedented security for future 5G+/6G wireless networks, Internet of Things (IoT), optical networks, and autonomous vehicles. In the first article paper [11], authors discuss the underwater QKD. Authors apply measurement-device-independent (MDI) QKD with the zero-photon catalysis (ZPC) performed at the emitter of one side to improve the SKR and extend the transmission distance. Numerical results indicate that the proposed ZPC-based scheme outperforms the corresponding single photon subtraction-based scheme in the extreme asymmetric case. In the second article paper [12], the author describes how to build the multipartite QCN based on the surface code (SC) concept. The key idea is to simultaneously entangle multiple nodes in an arbitrary topology based on the SC approach. The author also describes how to extend the transmission distance between nodes to beyond 1000 km using SCs. In the third article paper [13], authors introduce an open-destination MDI QKD network that provides security against untrusted relays and all detector side-channel attacks, in which all user users are capable of distributing keys with the help of other users. In the fourth article paper [14], authors introduce a QKD protocol which employs the mean multi-king problem in which a sender shares a bit sequence with receivers as a secret key.