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I have a 12.10 server setup in a virtual machine with its network set to bridged (essentially will be seen as a computer connected to my switch).

I installed opensshd via apt-get and was able to connect to the server using putty with my username and password.

I then set about trying to get it to use public/private key authentication. I did the following:

  1. Generated the keys using PuttyGen.
  2. Moved the public key to /etc/ssh/myusername/authorized_keys (I am using encrypted home directories).
  3. Set up sshd_config like so:

    PubkeyAuthentication yes
    AuthorizedKeysFile /etc/ssh/%u/authorized_keys
    StrictModes no
    PasswordAuthentication no
    UsePAM yes

When I connect using putty or WinSCP, I get an error saying No supported authentication methods available (server sent public key).

If I run sshd in debug mode, I see:

PAM: initializing for "username"
PAM: setting PAM_RHOST to "192.168.1.7"
PAM: setting PAM_TTY to "ssh"
userauth-request for user username service ssh-connection method publickey [preauth]
attempt 1 failures 0 [preauth]
test whether pkalg/pkblob are acceptable [preauth[
Checking blacklist file /usr/share/ssh/blacklist.RSA-1023
Checking blacklist file /etc/ssh/blacklist.RSA-1023
temporarily_use_uid: 1000/1000 (e=0/0)
trying public key file /etc/ssh/username/authorized_keys
fd4 clearing O_NONBLOCK
restore_uid: 0/0
Failed publickey for username from 192.168.1.7 port 14343 ssh2
Received disconnect from 192.168.1.7: 14: No supported authentication methods available [preauth]
do_cleanup [preauth]
monitor_read_log: child log fd closed
do_cleanup
PAM: cleanup

Why is this happening and how can I fix this?

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4 Answers 4

up vote 9 down vote accepted

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.

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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.

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SOLVED:

  1. You need to download the puttyGEN and generate a public and a private key.
  2. I've assigned a password to my private key.
  3. then configure the private key in putty. Putty->SSH->Auth->Browse to your private.
  4. Ensure you have the same path for private and public key.
  5. You need to configure the public key on the server. (In my case I've talked with the server guy and asked if he could add my public key to the server). You need the public key in the other side (server) the connection.
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In my case the reason was that private key file (.ppk) had been removed in Putty authentication agent i.e. Pageant. I just updated it again to Pageant there and connection worked perfectly after that.

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