This is the second part of our preliminary analysis of how Tor users interact with onion services [0]. In this part, we analyse the issue of onion service discovery. Onion services are private by default, so it's the operator's responsibility to disseminate their domain if they want it to be public. Question 3.6 in our survey asked:

How do you discover new onion sites?

The breakdown looks as follows. Respondents could select multiple answers, so the percentages are based on the total number of respondents. Method Percentage -----------------------------------------------------------------------

From social networking sites such as Reddit or Twitter 50.67 I browse the list of onion site search engines such as ahmia.fi 50.50 I randomly encounter them while browsing the web 47.65 Recommendations from friends and family 19.46 Other (see below for common themes) 18.12 I am not interested in learning about new onion sites 4.19

The data shows that social networking sites, search engines, and "random encounters" are rather popular. Respondents who selected "Other" mostly brought up onion service lists and aggregators. Following up, question 3.7 then asked:

Are you satisfied with the way you discover new onion sites?

61% selected "Yes" while the remaining 39% selected "No." Some respondents who selected "Yes" brought up that they have no interest in learning about new onion services; in part because they only use Facebook's (or some other) onion service. Among the respondents who selected "No," there are a bunch of reoccurring themes, in no particular order: - The most prominent complaint was about broken links on onion site lists. There is non-trivial churn among onion sites and our respondents were frustrated that existing lists are typically not curated and contain many dead links. - Many respondents were not aware of search engines such as ahmia.fi. Among those that were, many were not satisfied with both the search results and the number of indexed onion sites. Unsurprisingly, a "Google for onion sites" was a frequent wish. - Several respondents were unhappy with existing aggregators. In addition to broken links, some distrust lists because they occasionally contain scam and phishing sites. The difficulty of telling apart two given onion domain names exacerbates this issue. - Some respondents would like aggregators to be more verbose in their description of onion sites. In particular, these respondents were trying to avoid illegal and pornographic content, which is often difficult if the description is vague and the onion domain reveals nothing about its content. - Many respondents expressed frustration about the difficulty of finding out if site X also provides a corresponding onion service. A common wish was to have site X list its onion service prominently in a footer. Ironically, some respondents were surprised that torproject.org has a corresponding onion site -- they couldn't find it on the web site. - Two respondents compared the current state of onion services with the web of the 90s: Few sites existed, they linked to each other only sparsely, and search engines were experimental at best. - Interestingly, some respondents voiced frustration about various usability issues, but mentioned in the same sentence that this is an inherent trade-off of privacy technology, suggesting that there is nothing that can be done about it. There are two potential solutions that would address some of the above issues: - Have next-gen onion services opt-in to a broadcast mechanism that automatically propagates them. Naturally, we would like such a mechanism to be censorship-resistant and built in a way that only the owner of an onion service is authorised to broadcast their service. - Websites could use an HTTP header to announce the existence of a corresponding onion site. This issue was discussed in Feb 2017 over at tor-onions. Someone brought up the Alt-Svc header as a potential solution [1]. In a subsequent survey question we asked if our respondents would appreciate an automatic redirect from a web site to its corresponding onion site. The overall tendency leaned towards "Yes," provided that the implementation is sound and users can override the redirect. Again, it's important to take these results with a grain of salt. Our data has some survivor bias: Presumably, we mostly heard from people who are Tor users despite usability issues. We likely didn't hear from many people who once experimented with Tor or onion services, decided it's not usable enough, and gave up. The above was joint work with my colleagues Marshini Chetty, Annie Edmundson, Nick Feamster, and Laura M. Roberts. [0] <https://nymity.ch/onion-services/> [1] <https://lists.torproject.org/pipermail/tor-onions/2016-February/000045.html>