# Source Anonymity against Global Adversary in WSNs Using Dummy Packet Injections: A Survey
## 5 Global Adversary Models  
This section provides a detailed description of the used global adversary models in fake packet techniques, and how assumptions are made in each one of them. The _PeCo_ technique assumes that the adversary is able to deploy its own sensor network to monitor and analyze a _WSN_. Furthermore, the adversary network consists of a smaller number of nodes than the targeted network as the adversary only eavesdrops on the radio signals of legitimate nodes. Additionally, the adversary does not sense the environment, e.g., the authorized nodes. The adversary is also equipped with _GPS_ to detect the communication locations precisely [39]. The adversary is considered as _external_, _global_ and _passive_ in _ConstRat_, _ProbRate_ and _FitProbRate_ techniques. External means that the adversary cannot control or compromise a sensor node physically. Global means that the adversary has a full view of network communications as well as sufficient resources and unlimited power. Passive has three different aspects: First, an attacker cannot expose the content of a real event message that could lead to the source _ID_. Second, in the situation where messages are encrypted the same way during the forwarding process, the attacker has the capability to trace back the origin. Third, the adversary can apply complicated traffic analyses such as _Rate Monitoring_ and _Time Correlation_. In _Rate Monitoring_ attacks, the adversary focuses on the difference of the transmission rates between nodes, especially those nodes with higher rates. Nevertheless, the _Time Correlation_ attack works on the diversity of transmission times between transmitting packets. It is also assumed that the adversary has enough resources to apply all of these advanced attacks [32]. _Baseline, PFS, TFS_ and _OSAP_ techniques have the same assumptions for the adversary, which is _external_, _global_, and _passive_[33]. However, _OSAP_ provides more assumptions: First, the adversary knows the location of all nodes in the network. Second, it knows the distribution type of the _WSN_. Third, the adversary has the capability to compare its time interval observations with the known distribution type. Additionally, the adversary is assumed to be unable to disclose the content of packets or identify whether the packet type is real or fake [40]. In _RCM_, the adversary cannot decrypt the communications in the network. Therefore, packets appear completely random from the adversary perspective. Moreover, the adversary is aware of the sink location [41]. The _GFS_ technique builds its own technique based on the following adversary model assumptions. The adversary deploys its network to overhear the radio transmissions among legitimate nodes. Adversary nodes have unlimited processing power and battery life. The adversary can only eavesdrop  
Figure 8: The clustering mechanism. \(H\) is a cluster head. \(M\) is a cluster member. \(S\) is the sink. on the traffic, but it is unable to alter the traffic or compromise the sensor nodes. Data are encrypted and the adversary cannot gain any meaningful information about the packets' content. Further, real and fake packets are identical in size and structure making the adversary unable to distinguish the difference between them. Lastly, the adversary has knowledge about the sink location, the network topology, and the implemented routing protocol [42]. _NAA_, _GOA_, _HGA_ and _PBA_ techniques utilize a similar adversary model. This model assumes that the attacker knows the location of all sensor nodes in the targeted network. Moreover, the attacker has the ability to snoop on the traffic of the entire network. The adversary has enough resources to keep all collected data for further offline analyses. However, the attacker is unable to break the encrypted packets or compromise sensor nodes physically [43]. _DRAA_, _OFS_, _ASLP_ and _TESP_ techniques assume the popular _external_, _global_ and _passive_ adversary model [44; 45; 46; 48]. However, the adversary in _TCH-WSN_ can monitor the entire network traffic [47].