<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><br class=""></div><div class="">I have little useful opinion to add to this right now, but there is already an existing draft for an "Alternate Service" header - which may be relevant or inspirational:</div><div class=""><br class=""></div><div class=""> <a href="https://tools.ietf.org/html/draft-ietf-httpbis-alt-svc-09" class="">https://tools.ietf.org/html/draft-ietf-httpbis-alt-svc-09</a></div><div class=""><br class=""></div><div class="">At scale it might be costly to issue a header to all browsers in order to advertise an alternate service to some small fraction of people whom are actually able to (or desire) to use it.</div><div class=""><br class=""></div><div class="">Perhaps only issuing the header to people who access from an exit node, might reduce that cost?</div><div class=""><br class=""></div><div class=""> -a</div><div class=""><br class=""></div><div class=""><br class=""></div><div><blockquote type="cite" class=""><div class="">On Feb 4, 2016, at 14:16, MacLemon <<a href="mailto:tor@maclemon.at" class="">tor@maclemon.at</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">Hi!<br class=""><br class="">Just an idea:<br class="">What about announcing that your site is also available via onion-service by sending an x-onion HTTP response header on your HTTPS website?<br class=""><br class="">For example:<br class="">The clearweb site <a href="https://www.torproject.org/" class="">https://www.torproject.org/</a> could send a header like this:<br class="">x-onion:http://examplefoobarbaz.onion/<br class=""><br class="">Or in case you can actually provide a valid TLS certificate for your Onion:<br class="">x-onion:https://examplefoobarbaz.onion/<br class=""><br class="">Another idea would be to also provide the fingerprint of the to-be-expected TLS certificate. This could look like so:<br class=""><br class="">x-onion:cert-sha256="1h89m/yelEy6l1poFiXZQbJ1s6BkrOquBl7Fd+0EOO0="; <a href="https://examplefoobarbaz.onion/" class="">https://examplefoobarbaz.onion/</a><br class="">Similar to what is done with HPKP headers, but without pinning.<br class=""><br class="">Follow up question:<br class="">How could this be done with non-HTTP services? (XMPP, SMTP, etc.)<br class=""><br class="">Best regards<br class="">@MacLemon<br class="">_______________________________________________<br class="">tor-onions mailing list<br class=""><a href="mailto:tor-onions@lists.torproject.org" class="">tor-onions@lists.torproject.org</a><br class="">https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-onions<br class=""></div></blockquote></div><br class=""></body></html>