  Anonymity services have seen high growth rates with increased usage in the
past few years. Among various services, Tor is one of the most popular
peer-to-peer anonymizing service. In this survey paper, we summarize, analyze,
classify and quantify 26 years of research on the Tor network. Our research
shows that `security' and `anonymity' are the most frequent keywords associated
with Tor research studies. Quantitative analysis shows that the majority of
research studies on Tor focus on `deanonymization' the design of a breaching
strategy. The second most frequent topic is analysis of path selection
algorithms to select more resilient paths. Analysis shows that the majority of
experimental studies derived their results by deploying private testbeds while
others performed simulations by developing custom simulators. No consistent
parameters have been used for Tor performance analysis. The majority of authors
performed throughput and latency analysis.
