Key-Based SSH Logins With PuTTY - Page 2

4 Connect To The SSH Server

Now we can connect to our SSH server simply by clicking on Open.

If you connect to the server for the first time, a security warning pops up. This is because PuTTY doesn't know the server's host key yet, so it is safe to click on Yes. (If this happens again later on, this can mean that another server is now running under the same IP address, or that someone has broken in and changed the key.)

We have saved the username with which we connect in our profile settings, so we don't have to type it here again. We only have to specify that user's password:

Now this was the "normal" way of logging in, i.e., with a username and a password. If anyone else knows the username and password, he can log in, too. So if you have weak passwords and/or are the victim of a brute-fore attack, this can become a problem. Let's change that now.

 

5 Generate A Private/Public Key Pair

We can use PuTTYgen to create a private/public key pair. Start it by double-clicking its executable file. Make sure you select SSH-2 RSA under Type of key to generate and specify 1024 as the Number of bits in a generated key. Then click on Generate:

Please move the mouse pointer over the blank area during the key generation to generate some randomness:

Now a private/public key pair has been generated. Under Key comment, you can enter any comment; normally you use your email address here. Then specify a Key passphrase and repeat it under Confirm passphrase. You'll need that passphrase to log in to SSH with your new key. Then click on Save publick key and save it in some safe location on your computer. You are free to choose a filename and extension, but it should be one that lets you remember for which system it is.

Then click on Save private key. You can save it in the same location as the public key - it should be a location that only you can access and that you don't lose! (If you lose the keys and have disabled username/password logins, then you can't log in anymore!) Again, you're free to choose a filename, but this time the extension must be .ppk:

Then copy the public key from the PuTTYgen window:

 

6 Save The Public Key On The Server

Then log in to your SSH server (if you have closed the previous SSH session already), still with the username and password, and paste the public key into the file ~/.ssh/authorized_keys2 (in one line!) like this:

mkdir ~/.ssh
chmod 700 ~/.ssh

vi ~/.ssh/authorized_keys2

ssh-rsa AAAAB3NzaC1yc2EA[...]Lg5whU0zMuYE5IZu8ZudnP6ds= myname@example.com

That file must be write/readable only by that user, so we run

chmod 600 ~/.ssh/authorized_keys2

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From: FalconsMaze at: 2010-06-19 18:43:49

Thank you for the detailed screen shots and hand holding.  I was able to set this up in five minutes.  On other blogs there are a lot of steps omitted or :"your just suppose to know that setup."

Awesome job!

 

From: dcb at: 2012-08-16 09:13:49

This is well explained thank you. Putty does it's job well, but there are few instructions around that explain how to use it. The messages from failed login attempts rarely give any clues about how PuTTY should be set up. Many thanks for taking the time to document these settings and explain them so clearly. It is much appreciated.

David.

From: DizzyBum at: 2013-02-25 16:18:57

Thanks for this article!  I use Putty non-stop at work and this is going to cut out a lot of the time I spend copying and pasting long passwords.  Very clear and simple instructions.

From: Brian at: 2013-07-23 18:58:13

Thanks for explaining the whole process! I had stumbled through the key generation but couldn't figure out how to get the public key to the server in the right spot. I've bookmarked this page for future reference, because at my new job I've got a lot of servers to ssh to.

From: at: 2006-12-09 08:08:12

$HOME/.ssh/authorized_keys2 is deprecated and only still valid because of OpenSSH trying to be backward compatible, the actual file is $HOME/.ssh/authorized_keys, see the manual page of sshd.

From: at: 2006-12-12 16:42:03

There is no reason why '~/.ssh/authorized_keys(2)' cannot be globally readable, obviously you do not want it globally writable.

If someone was to take a copy of your public key the 'worst' they could do is give you access to an additional system.... :-/

No harm  in "chmod 0600"'ing but it does imply you have missed the meaning of 'public' in public key based authentication systems. I personally use 0644.

From: Gallomimia at: 2012-12-11 18:15:53

This is correct. It is the private key which must be made 600 on linux systems for them to be used as outgoing connections. In fact, 400 is a better permission mode.

 Speaking of outbound private keys, why can't I use my openSSH private key as is with putty?

From: Paulo at: 2008-12-13 00:44:46

Very nice how to, thanks!!! It worked for me.

From: at: 2008-12-17 14:28:03

Really good and clear explanation. Properly step-by-step, with screenshots all the way. Even a total beginner can follow this. Great job. Thanks.

From: Hb at: 2009-01-09 21:26:12

After pasting the clipboard to vi you will see Insert as status mode at the bottom of the screen. Now press Esc to get in command mode and then :wq and Enter to leave (and survive) vi.

On most systems nano is installed. Nano is probably easier to use.

From: spice at: 2011-07-20 20:36:22

I tried saving the public key as a file (on Windows), and then copied this multi-line file to my Unix server.  This didn't work.  I suspect end-of-line issues.

When I simply copied the public key from the field in Putty, and then pasted this single line into  ~/.ssh/authorized_keys things worked.

 

From: Anonymous at: 2011-09-28 11:03:23

great help!

From: Scott D. at: 2012-02-27 20:13:20

Hi, thanks for a tutorial that talks about Loading existing private keys. I managed to get putty connecting through SSH, with keys, to my Ubuntu Virtual Private Server.

From: at: 2006-12-08 09:11:10

I've always wanted to do this, but have never known how. This tutorial told me exactly what I needed to know. Thanks! 

From: at: 2006-12-10 19:23:45

There is a version of PuTTY called PortaPuTTY that can be installed to USB drives, without any Registry modifications.

From: Damian at: 2009-12-14 15:17:59

Just been pulling my hair out trying to get Windows to talk nicely to Ubuntu and this nailed it. Cheers Damian

From: Anonymous at: 2009-11-07 05:01:36

Thanks for this.

 This is a great site with lots of useful stuff explained in a clear and concise manner.

From: Mikeomillian at: 2010-03-20 14:49:02

I was actually trying to admin my VPS without command line, because I had tried putty once and it didn't work. This got it working in about 10 minutes, thank you!

From: Neil at: 2010-07-21 07:37:00

Thank you so much. Easy, step by step, and it just works.

 Wonderful.

From: Thiago Cruz at: 2010-07-27 14:31:18

Excelent step-by-step. I used it with plink. Thanks

From: TeHZomB at: 2011-01-28 04:57:51

Thanks, this guide is great and really easy to follow! Even five years later, works like a charm.

From: Mike G. at: 2011-05-04 16:54:52

Excellent tutorial -- it was very clear and well written.

From: Angel S. Moreno at: 2011-05-18 03:23:07

I've been using putty for a while but never made use of the tools or settings described. Super helpful.

From: metazone at: 2011-06-07 15:48:10

This should be a model for tutorials -- succinctly states why we need to do something and then provides a very nice explanation --

From: Michael at: 2011-08-10 11:17:07

Very clear and simple, thanks.

From: uptoome at: 2011-09-13 16:31:23

This worked right out of the box. Thank you.

From: KB at: 2011-12-10 19:31:47

Very well done and easy to follow directions.

I had problems with the keys generated by putty for some unknown reason, possibly due to not adding the username, though I'm not sure.

Instead, I generated them on the server using ssh-keygen -t rsa then copied the .pub key over to authorized_keys2 and downloaded the private key to my local machine (being sure to remove the private key from the server for security purposes afterward). I then was able to import the private key into PuttyGen and save it out as a .ppk file and work with the rest of your instructions.

From: Anonymous at: 2012-02-22 16:15:28

Thanks for this great tutorial! 

From: DreadfullyDespized at: 2012-03-07 03:58:35

This is a great article, thanks for this.  It worked great on my WD My Book Live 2TB.

From: Anonymous at: 2012-07-03 17:11:49

Drove me nuts - Listening on the wrong port in sshd_config, changed it because work think it is a safer to use the known port...

From: Fredy10 at: 2013-01-03 16:46:35

Very good how to! its very easy and clear!

Thanks!

From: krumov at: 2013-01-23 15:05:03

This is really Good HowTo which is clear enough for everyone , even the newest people who are touching the mouse and the keyboard for the first time ever.

Great !

From: David Coll at: 2013-04-22 03:58:15

Doing this will result in most frequent Server resused your key.

 You must create your private key on linux using "ssh-keygen", then import the private key in putty, save it on window for putty-use.

On server you do "cat id_rsa.pub >> authorized_keys2  "

 ..and voila.