# An Untraceable Data Sharing Scheme in Wireless Sensor Networks
## 2 Related Studies  
[PERSON] et al. [12] proposed an efficient and secure framework for authenticated broadcast/multicast by sensor nodes as well as for outside user authentication. Moreover, many secure data transmission schemes [13; 14; 15] were designed for cluster-based networks. To solve the orphan node problem, [PERSON] et al. [13] proposed a secure and efficient data transmission scheme based on identity-related digital signatures. Though these encryption-based data delivery schemes can properly hide the information in each package, they cannot prevent the adversary from locating the monitored targets by analyzing the transmission paths of the packages. Based on secure data transmission techniques, many source-location privacy protection schemes have been proposed.  
To defend against the global adversary, each source node in the network and all the nodes on the routing paths of the packages need to periodically send the real packages. Meanwhile, the other nodes need to send dummy packages in the same rhythm. Considering that all the nodes in the network have the same radio pattern, the adversary cannot accurately locate the source node but can monitor all the radio actions of all the nodes in the whole network. It is a tradeoff between the time delay of package delivery and the amount of data transmission. [PERSON] et al. [6] decrease the time delay by making the sensor nodes send the real package as soon as possible while keeping them indistinguishable from the dummy packages. In this way, though the time delay greatly decreases, the data transmission amount does not increase. To decrease the number of dummy packages, each cluster head can filter the dummy packages in [16] and, similarly, the scheme in [17] selects a set of sensor nodes as proxy nodes to filter the dummy packages.  
Except for global adversary, some other schemes were designed for local adversary. In phantom routing algorithm [8], the message generated by the source node first randomly walks for \(k\) steps before being transmitted to the sink node to defend against the local adversary. Considering that the fake source nodes are variable with a random location, it is difficult for the adversary to locate the real source node. In some cases, the walk steps conceal with each other and the message is close to the source node. To make each step effective, the authors provide two variants namely sector-based directed random walk and hop-based directed random walk. In this way, the packages can be far from the source node and this increases the security of the source node. The performance of some routing algorithms in defending against jamming attack can be found in [18]. Recently, [PERSON] et al. [4] proposed a cloud-based source-location-privacy protection scheme. Before sending the package to the sink node, the source node first constructs a cloud with irregular shape and all the nodes send the packages with the similar pattern to conceal the source node. Simulation results illustrate that these schemes can protect the source node to some extent and, meanwhile, the data transmission amount increases. However, all the above schemes provide an opportunity for the adversary to sketch the outline of the suspicious region and this is a huge threat to the security of the source node.