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I'm trying to setup ssh authentication with key files in stead of username/password. The client is a Windows box running PuTTY and the server is a Ubuntu 12.04 LTS server.

I downloaded puttygen.exe and had it generate a key pair. In /etc/ssh/sshd_config I have this line:

AuthorizedKeysFile %h/.ssh/authorized_keys

and on my client's public key file it says this:

---- BEGIN SSH2 PUBLIC KEY ----
Comment: "my@email.address.com"
ssh-rsa AAAAB3NzaC1yc2EAAAABJQAAAIEAr3Qo6T5XU06ZigGOd3eKvfBhFLhg5kWv8lz6
qJ2G9XCbexlPQGanPhh+vcPkhor6+7OmB+WSdHeNO652kTofnauTKcTCbHjsT7cJ
GNrO8WVURRh4fabknUHPmauerWQZ6TgRPGaz0aucU+2C+DUo2SKVFDir1vb+4u83
AV1pKxs=my@email.address.com
---- END SSH2 PUBLIC KEY ----

I copied the part from "ssh-rsa AAA" to "my@email.address.com" and put that in the file ~/.ssh/authorized_keys on my server (in my own homefolder). In PuTTY under Connection > SSH > Auth I entered the path to the private key it generated on my client and saved the session settings.

I restarted the ssh server with

sudo service ssh restart

Now if I load the profile in PuTTY (I verified the private key is still in Connection > SSH > Auth and that the path is correct) and run the profile, it says

Server refused our key

I tried putting the public key in a file under the directory ./ssh/authorized_keys/ but that didn't help so I used ./ssh/authorized_keys as a file, pasting the key in it. I also tried generating a private/public key pair on the server, putting the public key in ./ssh/authorized_files and loading the private one in PuTTY on my client. Rebooting the server didn't help either.

I found that the error may be solved by putting the key in a place outside the user's home folder but that's only useful if the home folder is encrypted, which this one is not.

Also tried generating a 4096 bit key, thinking perhaps 1024 was too short.

How can I get this to work? Thanks!

EDIT:

Ok, /var/log/auth.log said:

sshd: Authentication refused: bad ownership or modes for directory /home/vorkbaard/.ssh

Google tells me ~/.ssh/ should be 700 and and ~/.ssh/authorized_keys should be 600, so I did that. Now /var/log/auth.log says:

sshd: error: key_read: uudecode AAAAB3N [etc etc etc until about 3/4 of my public key]
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6 Answers 6

up vote 10 down vote accepted

Ok, it is fixed however I don't see how this is different from what I tried already.

What I did:

  • generate a key pair with puttygen.exe (length: 1024 bits)
  • load the private key in the PuTTY profile
  • enter the public key in ~/.ssh/authorized_keys in one line
  • # chmod 700 ~/.ssh
  • # chmod 600 ~/.ssh/authorized_keys
  • change /etc/ssh/sshd_config so it contains AuthorizedKeysFile %h/.ssh/authorized_keys
  • # sudo service ssh restart

For troubleshooting do # tail -f /var/log/auth.log.

Thanks for your help!

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1  
Hmm, so what happened to that sshd: error: key_read: uudecode AAAAB3N error in auth.log? –  Alaa Ali Jun 11 '13 at 13:27
    
I haven't a clue, Alaa. Perhaps I made an error pasting the previous key string. Auth.log doesn't get any more entries now and key based authentication works flawlessly. My main problem was that I wasn't really sure about what needed to be done, making the how that much more difficult. So I don't know why but it works. Thanks again for your help :) –  Captain Forkbeard Jun 11 '13 at 18:23
    
Awesome!!! I have been scratching my head for 2 days. This answers saves the day!! –  naka 10 hours ago
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The ~/.ssh/authorized_keys file requires keys to be all on one line. If you added it across multiple lines as in your paste above, try joining the lines.

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Thanks, that makes sense and now I understand why it is a file, not a directory. However it didn't help. –  Captain Forkbeard Jun 11 '13 at 12:07
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I had to change the ~/.ssh directory permissions from 770 to 700 and the ~/.ssh/authorized_keys file permissions from 660 to 600.

For some reason removing group permissions fixed this issue for me.

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
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In addition to all the above answers, make sure you copy and paste the key from puttygen correctly!

If you just double-click on the bulk of the key string to select it, you may not get the entire string, because the text box splits lines on some characters, like +, such that you don't select the text after the + character (which you can't see because the text box is too small). Be sure to select the entire string manually, from the ssh-rsa to the very end of the text box.

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I had to change permissions to home directory

chmod 700 ~
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Sometimes it can be a problem associated with having the public key on one line, this approach seems to solve it

echo 'the content of the public key' > /root/.ssh/authorized_keys
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