A First Look at References From the Dark to the Surface Web World: A Case Study in Tor

Tor is the most well-known anonymity network that protects the identity of both content providers and their clients against any tracking on the Internet. The previous research on Tor investigated either the security and privacy concerns or the information and hyperlink structure. However, there is still a lack of knowledge about the information leakage attributed to the links from Tor hidden services to the surface Web. This work addresses this gap by a broad evaluation on: (a) the network of links from Tor to the surface Web, (b) the vulnerability of Tor hidden services against the information leakage, (c) the changes in the overall hyperlink structure of Tor hidden services caused by linking to surface websites, and (d) the type of information and services provided by the domains with significant impact on Tor\u27s network. The results recover the dark-to-surface network as a single massive, connected component where over 90% of identified Tor hidden services have at least one link to the surface world. We also identify that Tor directories significantly contribute to both communication and information dissemination through the network. Our study is the product of crawling approximately 2 million pages from 23,145 onion seed addresses, over a three-month period