SSH Public Key - No supported authentication methods available (server sent public key)

Problem solved:

Looks like there was a problem with my public key file. PuttyGen will create a public key file that looks like:

---- BEGIN SSH2 PUBLIC KEY ----
Comment: "rsa-key-20121022"
AAAAB3NzaC1yc2EAAAABJQAAAIEAhGF6GIuMY8FJ1+CNApnSY1N2YSlkYz72Yvwu
a6N1nFpBklz1+dsIMg4rcTLcF34M/tW5Yz+NUDAw2AEbxQ32FPgw7sAOIXktkYOH
tr7mmimiTjkoSCrJh1kqalPSpi8rglT/Bp67Ql2SZwvUFfMzHISryR0EZC4rXP/u
vObrJe8=
---- END SSH2 PUBLIC KEY ----

However, this will not work, so what you need to do is to open the key in PuttyGen, and then copy it from there (this results in the key being in the right format and in 1 line):

ssh-rsa AAAAB3NzaC1yc2EAAAABJQAAAIEAhGF6GIuMY8FJ1+CNApnSY1N2YSlkYz72Yvwua6N1nFpBklz1+dsIMg4rcTLcF34M/tW5Yz+NUDAw2AEbxQ32FPgw7sAOIXktkYOHtr7mmimiTjkoSCrJh1kqalPSpi8rglT/Bp67Ql2SZwvUFfMzHISryR0EZC4rXP/uvObrJe8= rsa-key-20121022

Paste this into authorized_keys then it should work.

1. Edit the /etc/ssh/sshd_config file.
2. Change PasswordAuthentication and ChallengeResponseAuthentication to yes.

3a. Restart ssh /etc/init.d/ssh restart.
OR
3b. better you use service sshd restart

Just a tip I hope may help someone else with the headaches I had. F21 is right that you need to copy the key out of the PuTTYGen window instead of saving the file, but after copying, the way you paste may have significant impact on whether your key will work or not. Some editors will alter the text as you paste, or do something with newlines or something that makes the authorized_keys file invalid.

What I have found to be the least likely to break is to echo the full string and redirect the output to the file. Right-clicking in PuTTY to paste the key string to the commandline, it works out like this (with the example given above):

echo [right-click-to-paste-here] > /etc/ssh/username/authorized_keys

You'll end up with this:

echo ssh-rsa AAAAB3NzaC1yc2EAAAABJQAAAIEAhGF6GIuMY8FJ1+CNApnSY1N2YSlkYz72Yvwua6N1nFpBklz1+dsIMg4rcTLcF34M/tW5Yz+NUDAw2AEbxQ32FPgw7sAOIXktkYOHtr7mmimiTjkoSCrJh1kqalPSpi8rglT/Bp67Ql2SZwvUFfMzHISryR0EZC4rXP/uvObrJe8= rsa-key-20121022 > /etc/ssh/username/authorized_keys

Another advantage of this method is that you can add multiple keys this way by using >> to append instead of > to overwrite, eg:

echo ssh-rsa AAAAB3<...snip...>rJe8= rsa-key-20121022 >> /etc/ssh/username

Hope that helps someone.