Fwd: sk-api suggestions

Damien Miller djm at mindrot.org
Fri May 1 13:29:58 AEST 2020

On Fri, 6 Mar 2020, Damien Miller wrote:

> On Thu, 5 Mar 2020, Reza Tavakoli wrote:
> > Hello,
> > 
> > I'm helping the Git for windows team and contributing in git-for-windows
> > repository to help expand the OpenSSH support for fido2 devices on Windows.
> > Currently we are using your internal implementation(sk-usbhic.c) however
> > since Windows 10 version 1903 this requires administrator privileges.
> > 
> > I'm trying to create a module for OpenSSH to use webauthn.dll instead of
> > direct calling to libfido2 to eliminate the need for administrator
> > privileges
> > I noticed that in ssh-sk.c in function sshsk_sign you hash the input data
> > before passing it to external module sk_sign function. The problem is,
> > Windows API automatically hash the input before sending it to fido device,
> > so I need to receive the data without hashing to be able to use this or
> > else the data will be hashed two times and verification will fail.
> > 
> > May I suggest that you do this part inside sk_sign command so the module
> > using your sk-api.h interface can do this if it's needed?
> That sounds reasonable - do you have a patch you can share? We'd need to
> increase the SSH_SK_VERSION_MAJOR, but we'll probably do that before the
> next release anyway.


I committed a change to move the hashing from ssh-sk.c to the middleware,
bumping the expected middleware version along the way. Please take a look
(commit 59d2de956e).


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