u2f seed

David Lang david at lang.hm
Sat Jan 4 06:44:11 AEDT 2020

On Fri, 3 Jan 2020, Christian Weisgerber wrote:

> David Lang:
>> not supporting authentication from multiple machines seems to defeat the
>> purpose of adding u2f support.
> It works just like other SSH key types.  You have a private SSH key
> and a public one, and you can copy the private key to multiple
> machines or load it into ssh-agent and use agent forwarding.
> The only difference is that the private SSH key on its own is
> insufficient and requires the cooperation of the FIDO/U2F authenticator.

part of the value of u2f is that there is not anything that you need to install 
on every system.

turning u2f into just a way to unlock ssh keys may be an easy way to use a u2f 
key, but it's missing out on the value of u2f.

As I said, Google has a modified sshd that they use with u2f keys that does not 
require anything be copied or stored on the client machine.

Yes, it modifies the protocol to pass a server/application name, but why is it 
bad to add a new authentication mechanism? There is provision for the ssh 
protocol to issue a prompt for a password, that could be (ab)used to pass the 
name needed for u2f to work properly.

David Lang

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