# A Systematic Survey on 5G and 6G Security Considerations, Challenges, Trends, and Research Areas
## 3 5G Security Architecture: A Systematic Approach
### User Equipment
#### 3.3.2 D2D, V2X  
5G opens the possibilities for non-traditional communication methods, such as device-to-device (D2D) and vehicle-to-everything (V2X) methods. These two communication methods stem from the promises of 5G, allowing for even lower latency communication, larger device densities, and smarter transportation infrastructure. However, this brings with it new security considerations and challenges. The discussions in this section will focus on the considerations of D2D with V2X operations sharing many of these same requirements and concerns.  
The correct authentication of connections of IoT and D2D communications is of high importance for maintaining private and secure operations. The authors of [97] present a lightweight crypto algorithm to securely connect 5G IoT devices to each other over D2D all while not being vulnerable to security exploits or attacks. They also present four major factors when considering security for D2D, which are summarized in the list below:  
1. Authentication: Securing D2D communication requires authentication as one of the main aspects when connecting to the 5G IoT network. All networks need to have mechanisms in place to identify and verify users.
2. Data Confidentiality and Integrity: The use of hash functions and message authentication algorithms along with encrypted messages are vital to the confidentiality and integrity of the network. Prevalent concerns over these aspects stem from the number of eavesdropping, replay, and modification attacks that can occur if data are not secured.
3. Anonymity: The aspect of anonymity in a network is necessary so the identity of users is concealed and unknown to attackers. Anonymity prevents attackers from targeting specific users on the network. In the case of V2X, anonymity is paramount because when this principle is violated, an attacker could pinpoint a specific car, track its movement, and cause harm to an individual or a group of people.
4. Efficiency: As IoT devices have limited resources, it is important that they can request and obtain information on demand and without delay, as they are resource-constrained. The economical and efficient operation of communication systems is vital to the swift operations necessary in an IoT environment.  
Further discussions in [4] present potential privacy concerns of D2D communications. In [98], the authors propose Cross-Physical-Application-Layer Security for D2D links, which introduces channel conditions alongside cryptographic keys to authenticate connections between devices. This approach utilizes physical security methods, such as channel-based key agreements and channel-based entity authentication, and applies them to public key cryptography and symmetric encryption at the application layer. Other surveys and studies of D2D 5G networks are presented in [99; 100; 101]. In [99], the challenges and research opportunities in D2D cellular interference and physical security are outlined. [PERSON] et al. [100] propose a robust and efficient mutual authentication and key exchange method. The authors of [101] propose the use of biometric keys for stronger D2D link security.