EEeeZi·Jun 5, 2017
But YubiKeys are built on a hardened hardware security module instead of a general purpose phone operating system with full network connectivity and a huge attack surface.
Having a UI does not increase security in a meaningful way. The attacker is just going to wait until the victim connects to an interesting target server and then hijack that connection. The ControlMaster feature makes that trivially easy, but it's not hard to do real injection [1].
If the workstation is compromised, it's over.
At that point, all you can do is to prevent an attacker from copying the key or using it without user interaction. A YubiKey does both - you can optionally set it to a mode where you have to approve each signature.
With a bank transaction, the whole transaction is part of the approval process and can be verified out-of-band. With a SSH login, this
Read the rest
is not possible since you're still going to trust the workstation as soon as the session is established.
I'm not saying this project is useless - IF your phone is actually more secure than your workstation - which may or may not be the case - AND you've been previously been storing your keys on your workstation, then it's definitely a step up. But really, at that point, just buy a YubiKey (and properly secure your workstation!).
Otherwise, you now have TWO single points of failure instead of one. If either your phone or your laptop is compromised, it's over.
If you want login approvals that show the server name, do it as a second factor and use something like Duo Security with push approvals. This actually increases your security - instead of having, an attacker would now have to compromise both of your devices.
[1]: https://github.com/seastorm/PuttyRider