## 1 Introduction  
The 5G-enabled ultra-low-latency networks aim to open the door to the era of Internet of Actions, where things will be getting connected and becoming even more intelligent to provide service in a fully automated environment [1]. This new era of smart connectivity means that cybersecurity is expanded to physical space, with life or death situations appearing in critical services such as autopilot hacking [1]. In this context, the end-to-end distributed security strategy has been manifested as one of the key technological blocks of the research roadmaps addressing the security threats in the 5G and Beyond-5G (B5G) era [2]. Approaching the age of Quantum Computing (QC), the definition of a quantum-resistant security framework becomes a top priority for the 5G-oriented infrastructure owners and operators. This strategy relies on the use of Post-Quantum Cryptography (PQC) through unbreakable cryptosystems [3], as well on the exploitation of Quantum Key Distribution (QKD) which is based on the laws of physics only [4]. The PQC offers compatibility with the existing cryptographic infrastructure, it is only secured against known quantum attacks though [5]. In contrast, the unconditional security of QKD has been ensured through several one-time-pad demonstrations encryption across quantum networks [6]. Since the QKD is a symmetric key algorithm which cannot replicate all the functionalities of public-key cryptography [5], a joint PQC/QKD encryption scheme where quantum-resistant algorithms can have access to the secure shared key material from QKD has been manifested as the quantum-safe infrastructure layer [7]. In this direction, the development of hybrid key exchange protocols being resilient to the advances in quantum computing has emerged as an initial deployment candidate [8]. In the context of PQC, a range of algorithms is being evaluated under the NIST program [9], leading to Draft Standards in two to four years. Besides the standardization process, ADVA was recently presented through field-trials, PQC-based 100G safe optical transport over long-haul fiber links utilizing a public-key encryption system based on the variant of the Niederreiter scheme [10]. On the other hand, the major advantage of QKD is that it solves the key distribution problem in symmetric cryptosystems. Therefore, the distilled secret key can be used to encrypt a message using a symmetric algorithm, such as the Advanced Encryption Standard (AES), which is known to be quantum-resistant [11]. QKD offers a key distribution whose security is based on the most fundamental laws of nature and specifically on the laws of quantum mechanics and promises in principle unconditional security. However, even though the unconditional security of QKD has been proved for several protocols, such as the well-known BB84 [12; 13; 14], there is a gap between the ideal and the practical implementations of QKD protocols, which may lead to security loopholes, since the security proofs are commonly based on idealized setups. These security loopholes have triggered the scientific community to invent and, on a second stage, to implement more resilient schemes [4; 15]. Additionally, the QKD exchange requires an initial authentication step, which requires a pre-shared secret. This initialization step can be performed by quantum-resistant algorithms. Once QKD has been performed, the security of these algorithms is no longer important, since the distilled secret key has no algorithmic link to the pre-shared key used to authenticate the QKD exchange [16]. Furthermore, the practical implementation of QKD also faces many technological challenges at the moment, such as the relatively low detection rate, the difficulty of fabricating low-noise and high-efficiency photon counters and the task of increasing the communication distance [4]. However, in the last decade, many encouraging steps have been made by quantum technology vendors and research community dealing with these limitations [17; 18].