How to cite a site from the dark web? For my masters degree in computer science, I'm currently working on a paper on ransomware. Goal of this paper is to focus on academic writing and citing sources correctly.

Trustworthiness/Quality of sources

As I wanted to show what kind of business ransomware is and what amounts of money are dealt with, I had a look at the TOR onion network - a deep web only accessible by TOR browser. 

I found some interesting results. Despite the fact that the pages are completely anonymous and it's not sure if the authors can be trusted, would it be ok to cite those pages on ransomware-related questions, stating their poor trustworthiness immediately after the citation?

BibTeX

Other questions came up on how to cite these pages. My bibtex file now looks like this (I replaced some parts by * for obvious reasons):

@misc{Darknet:****,
    title={**** - The Better &amp; Cheapest FUD Ransomware + C&amp;C on Darknet},
    howpublished={\url{http://****.onion}},
    note={Abgerufen am 12.03.2017}
}


My question here is how to state that the *.onion url only works in TOR browser? Or should I better include a screenshot in case the page gets shut down?
Is it OK to cite? Yes.

But... While I recognize that some valuable information can only be obtained from the dark side, it is unfair to air a source’s opinion when the source’s identity and motives are shielded from scrutiny. 

So, describe the anonymous sources as clearly as you can. I totally agree with you: "stating their poor trustworthiness immediately after the citation". And note that not everybody knows that *.onion URLs only work in the Tor browser.

About the URL format, cite as any URL, as Anonymous Physicist recommends. I would also suggest you to create permanent records of the web page. Services like perma.cc might help you, it cannot resolve .onion domains, but you can upload your own archive. Another way can be find here.