# Privacy-Aware Access Protocols for MEC Applications in 5G +
## 3 Statement of the Problem
### Adversary Model
#### 3.2.1 Justification of the Adversary Model  
The parties in the system model, MNO, MEC, and APPIFY, are assumed to be honest-but-curious and passive Dolev-Yao adversaries.  
We assume that these parties are honest because they conduct business and care about their reputation. If they abuse the authority they have, for example, by selling the customer data to third parties, then they can obtain a bad reputation and lose the trust of the customers; an example case can be found in [47]. In consequence, they would likely comply with the regulations.  
A malicious actor may succeed in infiltrating one of these parties, e.g., one of the MNO employees is malicious. This is called an insider attack. We assume that each party has separate mechanisms to detect such attacks and procedures to prevent them, or at least for recovering fast. Therefore, we do not include attacks by malicious insiders in our adversary model.  
The parties can be curious about the customers to whom they provide services while still being honest. It is possible to learn the habits of the customers by analyzing their messages, e.g., which services they prefer, how often and when they use these services, and what, in general, is vital to customers. This analysis provides companies with an understanding of what customers want based on their previous behaviors [48]. In the system model, MNO and MEC transfer messages between Alice and APPIFY. MNO and MEC can retrieve these messages for further analysis. In addition, APPIFY might try to learn more about [PERSON] than what she shares with the application.  
We also assume that MNO, MEC, and APPIFY are passive Dolev-Yao adversaries. Both MEC and APPIFY have an opportunity to see the messages of [PERSON] when they are sent between Alice and MNO because radio communication is used. It is not as easy to arrange for APPIFY to receive the messages between MNO and MEC or for MNO to receive the messages between MEC and APPIFY. Still, we do not want to rely on the technical difficulties of such passive eavesdropping. However, all three parties are honest, so they do not interfere with the communication by rerouting, deleting, editing, or replaying the messages. Therefore, they are passive, not active, Dolev-Yao adversaries.  
We have three different types of entities that are all called outsiders. The first type contains elements that are not even visible in our system model. However, such elements can observe and interfere with the messages sent between the parties. Therefore, these elements can be viewed as Dolev-Yao adversaries. The second type consists of MNO subscribers other than [PERSON]. They might have malicious intentions and possess Dolev-Yao capabilities. It is straightforward to obtain a subscription or buy a prepaid card from MNO, and generally, such fresh subscribers do not have any reputation to lose. These other subscribers have legitimate access to MEC applications, which helps them perform various active attacks, e.g., denial of service (DoS). The third type of outsiders contains MEC applications in the MEC host, other than APPIFY. These applications are in a similar position as APPIFY in the system model. For similar reasons as explained above for the case of APPIFY, it is natural to assume that they are honest-but-curious adversaries with passive Dolev-Yao capabilities.  
[PERSON] is not an adversary in our system model because the assets we try to protect are her identities and data.