# Privacy-Aware Access Protocols for MEC Applications in 5G +
## 2 Review and Related Work
### Review  
We focus on three notions related to privacy: data confidentiality, identity confidentiality, and unlinkability.  
Confidentiality is \"_the act of preventing unauthorized entities from reading or accessing sensitive materials_\" [19]. In our paper, we focus on data and identity confidentiality. Data confidentiality means \"_protecting data against unintentional, unlawful, or unauthorized access, disclosure, or theft_\" [20]. Only the entities who require these data to provide services should have access to the data.  
Identity confidentiality can be defined as follows: \"_the permanent identity of a user to whom a service is delivered cannot be eavesdropped on the radio access link_\" [21]. The user might have various identifiers for MNO and MEC application. International Mobile Subscriber Identity (IMSI) is the permanent identifier of the subscriber in a mobile network. The IMSI is sent over the radio access link as rarely as possible in legacy mobile networks, and a randomly generated temporary identifier is sent instead. This randomly generated identifier is called the temporary mobile subscriber identity (TMSI) in 2G and 3G systems, and the globally unique temporary identifier (GUTI) in the 4G system. In the 5G system, the temporary user identity is called 5G-GUTI, and the permanent user identity is called the subscription permanent identifier (SUPI). For simplicity, we use the terms IMSI and TMSI to designate the permanent and the temporary identities of the mobile user throughout the rest of this paper, even when the discussion is about 5G. The identifiers should not be learned by parties who do not need them to provide services.  
The definition of unlinkability is given in [22]: \"_unlinkability of two or more items of interest from an attacker's perspective means that within the system, the attacker cannot sufficiently distinguish whether these items are related or not_\". We require the unlinkability of both messages and user identifiers.  
The following concepts are relevant to our work: virtual private network (VPN) and onion routing (OR). VPN helps to establish a secure private channel between two entities in a public network instead of building a private network by using the tunneling protocol [23]. The tunneling protocol enables a safe way of transport for network services that are not supported directly by the elemental network [24]. This way, data can be sent and received securely by cost-efficient and reliable methods in the public network. In addition to providing a secure connection, VPN helps to anonymize the traffic of the user on the internet. It also makes it harder for attackers to track the activities of the user over the internet [25].  
Onion routing constructs a layered object to direct an anonymous, bi-directional, real-time virtual circuit between two entities (sender and receiver) in the network [26]. In between the two communicating parties, there are several nodes, which are called onion routers. A default route exists of three routers: entry router (sender), intermediate router, and exit router (receiver) [27]. The number of intermediate routers can vary depending on the requirements of the route. The onion proxy knows the onion routers in the network and holds the information, such as IP addresses, public keys, and bandwidth, of these routers [27]. Then, the proxy determines the intermediate routers of the virtual path. The sender encrypts the messages layer by layer with the public keys of each router and sends the message. Each router decrypts its own layer and forwards the message to the next router. The receiver decrypts the last layer and reads the plaintext [28]. It should be noted that each router knows only the previous and next routers of the path, and the rest of the path stays anonymous [27; 28].