[tor-dev] User perception of onion service discovery

[Philipp Winter]

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>