George MacKerron: code blog

I’ve been unhappy for a while having the SSH daemon on my web server VPSs with password authentication enabled. Of course, it’s on a non-standard port, blocks root logins, and takes a strong-ish password… but the risk of a successful dictionary attack has still felt too non-zero for comfort.

Equally, though, I’ve not wanted to give up the ability to log in to the servers from anywhere to fix things in an emergency, so I didn’t want to turn password authentication off and rely on public keys alone.

Until now, that is. I realised yesterday that, since I have iSSH on the iPhone, which does public key authentication, I can log into my servers from anywhere, even with password authentication turned off. Granted, doing anything serious on a tiny screen and slow connection is difficult. But all I actually need to be able to do from there is temporarily turn password authentication back on.

And to make this easy, I’ve put two ultra-simple scripts in ~/bin:

pwd_login_on.sh

#!/bin/bash
sudo sed -r -e 's/^PasswordAuthentication no$/PasswordAuthentication yes/' \
  -i.previous /etc/ssh/sshd_config
sudo /etc/init.d/ssh restart

pwd_login_off.sh

#!/bin/bash
sudo sed -r -e 's/^PasswordAuthentication yes$/PasswordAuthentication no/' \
  -i.previous /etc/ssh/sshd_config
sudo /etc/init.d/ssh restart

(These paths are suitable for Ubuntu 8.04).

Lovely.