SSH login without password (authorized_keys)

http://diffract.me/2009/07/ssh-login-without-password-authorized_keys/

by nocivus • 17 years ago

17 24 17 years ago

Erwin• 17 years ago

1) You should definitely create a passphrase for your private key (you should only be asked to unlock it once due to ssh-agent). Otherwise if someone gets hold of your private key they can login to any machine you have set up an authorized_keys entry on.

2) use ssh-copy-id to install your public key on a remote (and fix up the permissions on ~/.ssh etc. which for me is the #1 case of key based login not working).

stuff4ben• 17 years ago

and fix up the permissions on ~/.ssh etc. which for me is the #1 case of key based login not working

DOH! I just spent the past 15 minutes trying to figure out why it wasn't working until I stumbled upon my .ssh directory having worldly permissions. Was just about to come here and post the same thing. chmod 700 is your friend!

jerf• 17 years ago

ssh -vv (with more or fewer vs) is also your friend. IIRC it tells you about the permission error either there or in the sshd log, and you can also find a lot more errors in the -vv output.

You should run ssh -vvv on a normal, working connection at least once to get a sense of what normal output is.

nocivus6• 17 years ago

Thanks for the cool explanation. I never really dug into ssh that much, just posting a helper to connect without password ;)

So basically ssh-agent should be always running and you add your key to it (via ssh-add) and you never enter your password again, but the key still is generated with a passphrase? Correct?

Thanks

tessro• 17 years ago

That's correct. And on OS X (at least on 10.5) you can put the key into your keychain and unlock it with your system password. Just make sure you lock your keychain when you don't need it.

nailer2• 17 years ago

This article is somewhat out of date. Modern OpenSSH distro's include 'ssh-copy-id', a single command to transfer, and append one's key to the remote list ofauthenores keys.

So:

Step 1:

    ssh-genkey

Step 2:

    ssh-copy-id user@host

Done.

yan• 17 years ago

Some operating systems, including OS X, don't provide that script, but it's easy enough to just download it: http://www.chiark.greenend.org.uk/ucgi/~cjwatson/cvsweb/~che...

jsonscripter• 17 years ago

ssh-copy-id is great, but the connection argument must be quoted, so if you need to use a different port you must use the form:

  ssh-copy-id 'user@host -p1337'

Took me far too long to figure this out :\

sant0sk1• 17 years ago

Actually, step 1 is:

    ssh-keygen

nailer2• 17 years ago

You're right. I'm used to verb-noun commands, which are more popular in Unix, and the only option in Powershell.

nocivus6• 17 years ago

Thanks for the tip :)

_pi• 17 years ago

Also ssh-copy-id will not work if you don't have password authentication enabled. The only way to get ssh keys on top a ssh box without password auth, is to download them with some other method.

tdavis• 17 years ago

Step 3:

Install Keychain (http://www.gentoo.org/proj/en/keychain/), so you can actually use a passphrase like a smart person and not have to deal with ssh-agent and ssh-add nonsense.

ovi256• 17 years ago

I connect to remote machines several times in a typical workday, and this helps to save a bit of time. Furthermore, it allows some non-obvious behaviour, like closing the connection as soon as I did what I wanted. This avoids leaving a ssh session open in which you may erroneusly type a command intended for your local machine. An "svn up" on the wrong machine car ruin your day.

Tichy• 17 years ago

Isn't that a bit of a security issue? One machine in the network hacked, they are all gone? Then again, hacker's could just install keyloggers if they get hold of one machine. But it would be a bit more effort.

dtf• 17 years ago

Speaking of which:

According to the MAN documentation for ssh-keygen, host keys must have an empty passphrase, so just leave it blank.

We're not making a host key here, are we? Shouldn't a passphrase be employed?

bcl• 17 years ago

He also flubbed using ssh-agent. Usually it is run from the login script once. You then do a ssh-add to add your identity to it. Once that is done you don't need to enter your password for that session anymore. You can even allow ssh on other systems to access your agent so you can ssh to another machine, ssh from that machine to a 3rd which will use your agent for the key info.

Never leave your key without a passphrase!

A good series of articles on ssh bt Brian Hatch can be found here - http://www.hackinglinuxexposed.com/articles/20021211.html

surki• 17 years ago

Some more SSH tips

1. Use SSH connection multiplexing

If you are connecting to same computer multiple times, this saves up quite a bit of time http://www.revsys.com/writings/quicktips/ssh-faster-connecti...

2. Use autossh

For a persistent ssh connection (ex. for reverse tunnels) http://www.debianadmin.com/autossh-automatically-restart-ssh...

antipax2• 17 years ago

Obscuring his public key tells me this guy doesn't quite understand what the point of public-private key encryption is.

nocivus6• 17 years ago

I know the public key is supposed to be public, hence no point in obscuring. I just got carried away ;)

antipax2• 17 years ago

My apologies if I offended you; I just wanted to point it out.

nocivus6• 17 years ago

Thanks for all the tips, everyone :D

SSH login without password (authorized_keys)

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