U2F support in OpenSSH HEAD

Jordan J jordandev678 at gmail.com
Sun Nov 3 09:04:58 AEDT 2019

I've had a patch on the bugzilla for a while related to U2F with
support for a few additional settings such as providing a path to a
specific key to use instead of the first one found and setting if user
presence is required when using the key. Is there any objection to
folding those parts in if appropriate?

Joseph, to offer comment on NIST P-256. There was originally quite a
limited subset of support in U2F, originally ES256 or RS256. There's
since been more added (Ed25519 appears to be one of them at a cursory
glance). If you take a look at param.h in the libfido2 repository
you'll see the list of supported algorithm constants (COSE_*). From
personal experience though I've had a few different brands of
pure-u2f-only tokens and never seen support for anything other than
P-256 in the wild. Yubicos U2F only keys for example are currently
listed on their site as only having P-256 support. I imagine
multi-purpose keys might have more expansive support though. RS256
also appears to be marked as deprecated.

On Sat, Nov 2, 2019 at 7:54 PM Joseph S. Testa II
<jtesta at positronsecurity.com> wrote:
> On 11/1/19 4:36 AM, Damien Miller wrote:
> >  new key type "sk-ecdsa-sha2-nistp256 at openssh.com"
> Was ECDSA with NIST P-256 strictly necessary, or would Ed25519 be
> possible as well?
>     Thanks,
>     - Joe
> --
> Joseph S. Testa II
> Founder & Principal Security Consultant
> Positron Security
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