The following submission constitutes a guide and an introduction to a collection of articles submitted as a Ph.D. dissertation at the University of Gda\'nsk. In the dissertation, we study the fundamental limitations within the selected quantum and supra-quantum cryptographic scenarios in the form of upper bounds on the achievable key rates. We investigate various security paradigms, bipartite and multipartite settings, as well as single-shot and asymptotic regimes. Our studies, however, extend beyond the derivations of the upper bounds on the secret key rates in the mentioned scenarios. In particular, we propose a novel type of rerouting attack on the quantum Internet for which we find a countermeasure and benchmark its efficiency. Furthermore, we propose several upper bounds on the performance of quantum (key) repeaters settings. We derive a lower bound on the secret key agreement capacity of a quantum network, which we tighten in an important case of a bidirectional quantum network. The squashed nonlocality derived here as an upper bound on the secret key rate is a novel non-faithful measure of nonlocality. Furthermore, the notion of the non-signaling complete extension arising from the complete extension postulate as a counterpart of purification of a quantum state allows us to study analogies between non-signaling and quantum key distribution scenarios.

翻译：以下内容构成了一份指南与导论，旨在介绍一组作为格但斯克大学博士论文提交的文章集合。在该博士论文中，我们以可达密钥率的上界形式，研究了选定量子与超量子密码学场景中的基本限制。我们探讨了多种安全范式、双方与多方设定，以及单次与渐近机制。然而，我们的研究不仅限于推导上述场景中密钥率的上界。特别地，我们提出了一种针对量子互联网的新型重路由攻击，为此我们找到了对策并对其效率进行了基准测试。此外，我们提出了关于量子（密钥）中继器性能的几个上界。我们推导出了量子网络秘密密钥协商容量的下界，并在双向量子网络这一重要情形中对其进行了收紧。此处推导出的压缩非定域性作为密钥率的上界，是一种新颖的非忠实非定域性度量。此外，由完全扩展假设导出的非信号完全扩展概念，作为量子态纯化的对应物，使我们能够研究非信号与量子密钥分发场景之间的类比关系。