View Full Version : [ubuntu] Checking passphrases on ssh keys

July 3rd, 2008, 01:52 PM

I'm digging around and trying to figure out if there is a way to enforce passphrases on ssh keys. As you know, if there isn't a passphrase on the key and somebody grabs it, they can login to the system as you.

What I'm trying to do is configure sshd to not accept a connection from a ssh key that isn't password protected. If that isn't possible, is there a way to check the public key stored on the server to ensure the private key has a passphrase?


July 3rd, 2008, 08:17 PM
There is no way for a remote server to figure out if the private key being used for a connection has a passphrase or not. The only way you can test for this condition is to be on the machine where the private key is stored and examine the key file directly.

July 4th, 2008, 11:28 PM
you should definitely add pass phrases to all your keys. you can use puttygen to add a pass phrase to private key (your key pair will still be valid). or ssh-keygen of course.
ssh-keygen -p [-P old_passphrase] [-N new_passphrase][-f keyfile]

July 5th, 2008, 03:08 AM
This is just an idea, I have no clue how to do it, but maybe there is a way to configure sshd to ask for an rsa key and a passphrase. That way if one or the other is compromised there is a second safety net. Beside, that way you always have the control on the password policy (length and such) on the server.