<p>For the privacy aspect, see "De-anonymizing Users of French Political Forums" (<a href="http://archive.hack.lu/2013/dbongard_hacklu_2013.pdf">http://archive.hack.lu/2013/dbongard_hacklu_2013.pdf</a>) in which 70% of email addresses of contributors to a French forum were successfully brute-forced through the Gravatar hash. </p>
<p><a href="https://github.com/ppawel" class="user-mention">@ppawel</a>, you misunderstand when you write "I already opted in by registering with gravatar"; even for users who have never registered with gravatar, we publish their email hash in a Gravatar link (go to a random recent user's profile page on OSM, view source, and look at the Gravatar link in there).</p>
<p>In all privacy discussions we tell people that they are not forced to reveal their identity - "just choose a nickname and nobody gets to know who you are". It kind of defeats that argument if automatic Gravatar integration leads to easy decypherability - yes, people can switch it off, but we don't even make an attempt to explain anything to them so why should they.</p>
<p><a href="https://github.com/tomhughes" class="user-mention">@tomhughes</a> you are correct when you say that we are not "sharing email addresses" and therefore <a href="https://github.com/apmon" class="user-mention">@apmon</a> overstates the problem when he speaks of a "clear violation" of the privacy policy, but on the whole I think that shouting out the MD5 sums of the email addresses of our users is indeed a problem.</p>
<p>Even if someone doesn't apply a cluster of GPUs to guess email addresses, the question "does user SlickJoe123 use the email address <a href="mailto:freddy.krueger@gmail.com">freddy.krueger@gmail.com</a>, because his edits sure look like they could be Freddy's" is trivially answerable from SlickJoe123's email hash that we publish. </p>
<p>I for one would welcome <a href="https://github.com/apmon" class="user-mention">@apmon</a>'s patch.</p>
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