On Wed, Nov 5, 2014 at 7:21 AM, Michael Stapelberg <stapelberg+openssh@xxxxxxxxxx> wrote: > Hey, > > Recently, the FIDO alliance announced U2F [1], and Google announced > that it supports U2F tokens (“security keys”) for Google accounts [2]. > As the spec is not a very short read, I gave a presentation last week > about U2F which may be a good quick introduction to the details [3]. > For the rest of this mail, I’ll assume that you read either my > presentation or the spec, but feel free to post any questions about > U2F and I’ll try to answer them. (side note: I’m not working on U2F, > playing around with it and implementing it in OpenSSH is my private > fun project :)) > > I’ve spent some time (together with Christian and Thomas) hacking on > U2F support in OpenSSH, and I’m happy to provide a first patch — it’s > not complete, but it should be good enough to get the discussion going > :). Please see the two attached files for the patch. Due to their > size, I’ve not posted them in-line. > > The way it currently (!) works: > > 1) Use “AuthenticationMethods publickey,u2f” in sshd_config (or <whatever>,u2f) > 2) Recompile SSH with the patch and change userauth_u2f() to use > packet_put_int(0) (== registration) instead of packet_put_int(1) (== > authentication). Sorry about that. See my question below. > 3) You need to do this step only once: ssh into your server, touch > your security key when prompted, and you’ll see a ssh-u2f key line, > which you should copy&paste into the server’s ~/.ssh/authorized_keys > for the corresponding user. > 4) Recompile with packet_put_int(1). > 5) ssh into your server, touch your security key when prompted, enjoy > the additional security :). > > There are a couple of open questions: > > 1) Will you accept this patch (let’s ignore details for now) at all? > Everyone I’ve talked to in the last couple of days was pretty excited > about having U2F support in OpenSSH, so I think it’d be a great > feature. > > (the rest are detail questions about the implementation) > > 2) Could we make the server write to authorized_keys to avoid the > copy&paste step? Probably not a good idea, but I figured I’d ask > anyway. > > 3) What would be a good way to trigger the different U2F modes on the > client? Should we add a new flag to ssh(1)? Registration is very > rarely triggered, authentication should be the default. > > 4) What should we use as U2F appid? Currently I just set > “ssh://localhost” (it must be a URL), and we could use > “ssh://<hostname>”. Christian suggested using the host key > fingerprint, which would decouple the appid from the hostname (which > may be good if the hostname frequently changes, because U2F security > keys are registered for a specific appid). > > 5) What should we use as the origin (in the ssh client)? In the case > where U2F is used by a web browser, this is set to the canonical > representation of the domain (i.e. lowercased, after idn etc.). At the > moment, I’m using either the host alias or the hostname. Is that > acceptable or is there a better method? > > 6) Not a question, but a note: the patch does not yet handle multiple > registered U2F security keys. > > 7) I’d like to use SSL_load_error_strings() so that the human-readable > error messages actually contain some content and are not just NULL :). > It’ll require linking with -lssl. Is that okay or is there a reason > why we don’t do it so far? > > Thank you very much for any replies :). I haven’t seen any replies yet, and it’s been almost a week. It could just be that none of you care, or all who care are incredibly busy. Still, I’d appreciate a “don’t know about the details, but we’ll most likely merge your patch” so that I know any further work on this is not in vain :). Thank you! > > [1] https://fidoalliance.org/ > [2] http://googleonlinesecurity.blogspot.ch/2014/10/strengthening-2-step-verification-with.html > [3] https://www.noname-ev.de/w/File:C14h-u2f-how-security-keys-work.pdf _______________________________________________ openssh-unix-dev mailing list openssh-unix-dev@xxxxxxxxxxx https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
