HOWTO SSH without a password

From Gentoo Linux Wiki

The following instructions describe how to setup your SSH server to accept password free logins.

[edit] Client setup

As there exists two version of the SSH protocol, version 1 and 2, the identities are tied to the protocol version. Most SSH-servers use version 2 of the protocol due to the limitations of version 1.

List over protocols and their identity types:

After determining which identity type you want it is time to create your private and public ssh keys (in the article we use DSA encryption), on the client machine type:

$ ssh-keygen -t dsa
Generating public/private dsa key pair.
Enter file in which to save the key (/home/gerard/.ssh/id_dsa):

The default location is fine, so just press <enter>

Enter passphrase (empty for no passphrase):

Enter a passphrase or press <enter> again for an empty passphrase.

Enter same passphrase again:

Press <enter> again

key fingerprint is:
6f:c5:86:c7:67:69:02:1a:e4:a9:20:e6:16:13:5d:e5 username@host

That process created two files in ~/.ssh:

-rw-------   1 bob users   668 Jun 17 23:52 id_dsa
-rw-r--r--   1 bob users   602 Jun 17 23:52 id_dsa.pub

[edit] Server setup

The file named id_dsa.pub is your public key, which you should copy to the server (here referred to as remotebox). The file should be appended to a file named ~/.ssh/authorized_keys on the server.

Copy and install the id_dsa.pub file to the remote system:

$ ssh-copy-id -i ~/.ssh/id_dsa.pub username@remotebox

[edit] Client & Server Setup (Alternative with ssh-installkeys)

This part describes how to use the ssh-installkeys tool. It will do the steps explained above automatically. First install ssh-installkeys:

$ echo "net-misc/ssh-installkeys" >> /etc/portage/package.keywords
$ emerge -av net-misc/ssh-installkeys

And run it:

$ ssh-installkeys username@remotebox

ssh-installkeys will do all needed task to setup the local keyfiles and the remote login, which includes:

• creating a keypair on the local system (if there is none)
• logging into the remote system (the password is needed)
• adding the publickey to the remote system's ~/.ssh/authorized_keys
• checking and adjusting the security settings of the local and remote ssh files.

[edit] Alternative to keychains: Using ssh-agent

Using ssh-agent, your computer will store your private keys in memory for the duration of your session, or for a fixed time (if desired - see man ssh-add). It is intended for users who protect their keys with a passphrase, and allows the passphrase to be entered in once only: when the key is added to the agent. This setup is infinitely more secure than making a key with an empty passphrase (assuming you don't leave the session open for someone else to use, of course). To use ssh-agent, you commonly invoke it in one of two ways:

1. You can tell ssh-agent to create a child process (such as an X or Konsole session), and it will terminate automatically when the child process exits:

For example, in your .xinitrc:

exec /usr/bin/ssh-agent startkde

...or as an alias to konsole (or put this in the application line of the icon):

alias konsole="/usr/bin/ssh-agent /usr/kde/x.x/bin/konsole"

Gnome users are already running their session through ssh-agent if they use GDM.

2. You can invoke ssh-agent manually at the prompt:

$ eval `ssh-agent`

Once you have started ssh-agent or verified that it is running, add your keys with ssh-add:

$ ssh-add
Enter passphrase for /home/<you>/.ssh/id_rsa: 
Identity added: /home/<you>/.ssh/id_rsa (/home/<you>/.ssh/id_rsa)

Without arguments, ssh-add adds some default keys (if they exist): ~/.ssh/id_rsa, ~/.ssh/id_dsa, ~/.ssh/identity. If you have additional keys with other names, specify the files on the command line:

$ ssh-add ~/.ssh/gentoo_id_dsa

If you want ssh-agent to discard your key from memory after a time, specify the key's lifetime with the -t option:

$ ssh-add -t 2h ~/.ssh/sourceforge_id_rsa

See man sshd_config for time formats.

That's it. ssh-agent will supply your private keys to your SSH client processes whenever they are needed to authenticate with a server, without prompting for your passphrase each time. This is especially useful for scripting using SSH and running commands on multiple hosts.

[edit] Testing

$ ssh -l username remotebox
Last login: Thu Jun 17 23:55:36 2004 from 192.168.34.2
$

If the system did not query you for a password everything is working properly. If it did not work check your sshd_config file. The following options should be set:

# Allow Identity Auth for SSH1?
RSAAuthentication yes

# Allow Identity Auth for SSH2?
PubkeyAuthentication yes

Now repeat the Server-part for every server you want to be able to login into without specifying the password.

You can add the following line to your ~/.bashrc to be able to have root access to your box without having to give your root password.

alias root="ssh -l root 127.0.0.1"

Be carefull with this, cause anyone with access to your box will be able to issue this command!

[edit] Warning

[edit] Internal links

• TIP keychain
• Fast Copy Over SSH

[edit] External links

• ssh-keyinstall
• Keychain
• ssh-agent manpage