RFC: More explicit ssh agent forwarding on SSH_ASKPASS confirmation

Daniel Kahn Gillmor dkg at fifthhorseman.net
Wed Apr 3 11:20:41 EST 2013

On 04/02/2013 06:13 PM, Ángel González wrote:

> It would be desirable to have instead a text like:
> Confirmation is required before allowing usage of key foobar
> Key fingerprint abcdf.
> to process 1234 (ssh example.com rsync --server --sender -logDtpre.iLsf)

this material itself could be presented to the user even without changes
to the protocol.

> allegedly for "connecting to example.com ("

this line would need some protocol extension.  The SSH_FORWARDING_NOTICE
protocol detail you've referenced does *not* seem to cover this case,
but as you noted, you could use it for inspiration.

It seems like the first step would be to implement the prompting you
describe without the protocol changes and get people using it and giving
feedback on whether they find it useful.  This would probably be just a
patch to ssh-agent, no need to change ssh or ssh-askpass or anything
else.  I'd be happy to review and test such a patch, if you post it
someplace publicly.

I'm less convinced of the usefulness of the advisory strings, and they
have a higher bar to meet in the first place since they require changes
to the protocol to get them through to the agent.  is there a way to do
version or feature negotiation on the channel so that clients can fall
back to not providing advisory strings to an agent that might reject or
crash on them?


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