Ability to auth in the SSH backdoor using a private key

[unixfox]

I've seen some openssh backdoor that rely on private key to authenticate, maybe it could be great to add an option to use a public key instead of password in vlany? It would be more secure as passwords can be bruteforce while keys it's impossible.

[mempodippy]

I've seen this before too actually, but I'm not sure about with LD_PRELOAD hooking - however, it would be a neat feature. It's not incredibly important though. Only in some kind of weird case would someone be able to even begin bruteforcing the password.