Security, information, and structure characterization of Tor: a survey

Content on the World Wide Web that is not indexable by standard search engines defines a category called the deep Web. Dark networks are a subset of the deep Web. They provide services of great interest to users who seek online anonymity during their search on the Internet. Tor is the most widely used dark network around the world. It requires unique application layer protocols and authorization schemes to access. The present evidence reveals that in spite of great efforts to investigate Tor, our understanding is limited to the work on either the information or structure of this network. Also, interplay between information and structure that plays an important role in evaluating socio-technical systems including Tor has not been given the attention it deserves. In this article, we review and classify the present work on Tor to improve our understanding of this network and shed light on the new directions to evaluate Tor. The related work can be categorized into proposals that (1) study the security and privacy on Tor, (2) characterize Tor’s structure, (3) evaluate the information hosted on Tor, and (4) review the related work on Tor from 2014 to the present.