Table 2.

The 6G technologies, security challenges, and related work basic contributions.

6G Physical Layer Technology	Related Work	Security and Privacy Challenges	Basic Contributions
THZ	Akyildiz et al. [81]	Authentication	They discuss the electromagnetic signatures of THz frequencies that may be employed in physical layer authentication procedures.
	Ma et al. [82]	Malicious behaviors	They claim that an eavesdropper can capture a THz signal by using narrow beams. Moreover, they talk about a means of resisting this type of attack.
VLC	Pathak et al. [91]	Malicious behaviors	They highlighted what the victim’s line of sight should be if the adversary intends to conduct an attack on the current VLC process.
	Ucar et al. [92]	Privacy of communication	They introduced a SecVLC protocol to protect the privacy of data transmissions over vehicular networks.
	Mostafa et al. [93]	Encryption	They proposed a precoding technology that guarantees the efficiency of the physical layer and could improve the security.
	Cho et al. [95]	Malicious behaviors and security of the physical layer	They have proven that there could be a potential degrade in VLC safety by collaborating with eavesdroppers.
Molecular communication	Farsad et al. [96]	Malicious behaviors and authentication problems	An extensive overview of current molecular communication developments.
	Lu et al. [97]	Molecular communication reliability and encryption	To improve the reliability of transferred data inside a molecular communication system, two different codes are used for the first time. Both codes are Euclidean-Geometry Parity-Check (EG-LDPC) and cyclic-Reed-Muller (C-RM) code.
	Loscri et al. [98]	Authentication challenges and different attacks	Offering some initial insights on the issues of MC system privacy and security. Explores numerous ways for attacking molecular medium at various levels.
AI and ML technology	Dang et al. [114]	Authentication	Claim that AI design might support in identifying network problems in the 6G security and provide prevention approaches and protection solutions.
	Zhou et al. [113]	Access control and authentication	Explores AI technologies as well, claimed to detect security risks in advanced computing in greater detail.
	Sattiraju et al. [110]	Authentication	They proposed an efficient learning approach to improve the security of the physical layer in the authentication process.
	Hong et al. [111]	Communication	Presented an antenna design for classification tasks that must be used in communication with the physical layers to prevent any information leakage.
	Nawaz et al. [112]	Encryption	The proposed protection for the communication links in 6G networks using machine learning techniques and quantum encryption solutions.
Quantum communication	Hu et al. [119]	Quantum secret sharing, key management, and security of direct communication	Ensure the proper security of quantum communication. The experiment showed clearly the possibility of direct quantum-safe communication during a noisy and lossy environment. They also reported the first experiment based on a DL04 protocol and the coding for the frequency of a single-photon, which has validated block transmission.
	Zhang et al. [120]	Encryption	They allow the transmission of encrypted messages through a direct channel without using a private key. Providing fundamental steps towards practical quantum secure direct communication (QSDC) for long-distance quantum communication using quantum memory.
	Nawaz et al. [112]	Encryption of secret key	Using machine learning techniques to support key security.
Distributed ledger technology	Ling et al. [130]	Authentication	They proposed a novel network radio access architecture based on blockchain (B-RAN) to develop a secure efficient decentralized mechanism to manage authentication procedures and network access among many network components.
	Kotobi et al. [131]	Access control	They presented a way to enhance media access protocol and cognitive radio safety by leveraging the blockchain to obtain access to the unused licensed spectrum.
	Ferraro et al. [133]	Access control	They provide a framework for the application of Distributed Ledger Technology (DLTs) as a social compliance control mechanism in smart city environments that can improve the security against double-spending attacks.