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---
layout: default
title: SSH key passphrases
description: SSH key passphrases, why you should use them, and how to avoid re-entering them
categories: intermediate
---
<p class="intro">This guide will step you through the process of securing your ssh keys while avoiding re-entry of your passphrase every time you use the key.</p>
h2. Why do I need a passphrase?
Passwords aren't very secure, you already know this. If you use one that's easy to remember, it's easier to guess or brute-force. If you use one that's random it's hard to remember, and thus you're more inclined to write the password down. Both of these are Very Bad Things™. This is why you're using ssh keys.
But using a key without a passphrase is basically the same as writing down that random password in a file on your computer. Anyone who gains access to your drive has gained access to every system you use that key with. This is also a Very Bad Thing™. The solution is obvious, add a passphrase.
h3. But I don't want to enter a long passphrase every time I use the key!
Neither do I! Thankfully, there's a nifty little tool called @ssh-agent@ that can save your passphrase securely so you don't have to re-enter it. If you're on OSX Leopard or later your keys can be saved in the system's keychain to make your life even easier. Most linux installations will automatically start @ssh-agent@ for you when you log in.
h2. Adding or changing a passphrase
Passphrases can be added to an existing key or changed without regenerating the keypair very easily:
<pre class="terminal">$ ssh-keygen -p
Enter file in which the key is (/Users/tekkub/.ssh/id_rsa):
Key has comment '/Users/tekkub/.ssh/id_rsa'
Enter new passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved with the new passphrase.</pre>
If your key already has a passphrase, you will be prompted to enter it before you can change to a new passphrase.
h2. Auto-launching ssh-agent on msysgit
You can run @ssh-agent@ automatically when you open bash by adding the following to your @~/.profile@ or @~/.bashrc@ file:
{% highlight bash %}
SSH_ENV="$HOME/.ssh/environment"
# start the ssh-agent
function start_agent {
echo "Initializing new SSH agent..."
# spawn ssh-agent
ssh-agent | sed 's/^echo/#echo/' > "$SSH_ENV"
echo succeeded
chmod 600 "$SSH_ENV"
. "$SSH_ENV" > /dev/null
ssh-add
}
# test for identities
function test_identities {
# test whether standard identities have been added to the agent already
ssh-add -l | grep "The agent has no identities" > /dev/null
if [ $? -eq 0 ]; then
ssh-add
# $SSH_AUTH_SOCK broken so we start a new proper agent
if [ $? -eq 2 ];then
start_agent
fi
fi
}
# check for running ssh-agent with proper $SSH_AGENT_PID
if [ -n "$SSH_AGENT_PID" ]; then
ps -ef | grep "$SSH_AGENT_PID" | grep ssh-agent > /dev/null
if [ $? -eq 0 ]; then
test_identities
fi
# if $SSH_AGENT_PID is not properly set, we might be able to load one from
# $SSH_ENV
else
if [ -f "$SSH_ENV" ]; then
. "$SSH_ENV" > /dev/null
fi
ps -ef | grep "$SSH_AGENT_PID" | grep ssh-agent > /dev/null
if [ $? -eq 0 ]; then
test_identities
else
start_agent
fi
fi
{% endhighlight %}
p(. *Note:* If you don't use the default key names, or store your keys in a different path, you will need to add the path to the @/usr/bin/ssh-add@ line so that ssh knows where to find your key.
Now when you first run git bash, you will be prompted for your passphrase:
<pre class="terminal">Initializing new SSH agent...
succeeded
Enter passphrase for /c/Users/Tekkub/.ssh/id_rsa:
Identity added: /c/Users/Tekkub/.ssh/id_rsa (/c/Users/Tekkub/.ssh/id_rsa)
Welcome to Git (version 1.6.0.2-preview20080923)
Run 'git help git' to display the help index.
Run 'git help <command>' to display help for specific commands.
[Tekkub@KAKU: ~ master]$</pre>
The process will continue to run until you log out, shutdown or kill ssh-agent. To kill the process, find its PID with @ps@ then call @kill <PID>@:
<pre class="terminal">[Tekkub@KAKU: ~ master]$ ps
PID PPID PGID WINPID TTY UID STIME COMMAND
3796 1 3796 3796 ? 500 18:07:43 /bin/ssh-agent
2780 1 2780 2780 con 500 18:10:50 /bin/bash
3400 2780 3400 784 con 500 18:13:31 /bin/ps
[Tekkub@KAKU: ~ master]$ kill 3796</pre>
p(. <em>This section was written with help from "this post":http://www.cygwin.com/ml/cygwin/2001-06/msg00537.html.</em>
h2. Mac OSX Keychain
If you are on OSX Leopard or later, ssh-agent is run automatically for you. It will also integrate with the keychain, so you can unlock your keys with it. This has some major advantages over a command-line based setup like protecting your input from being copied or spied upon by universal access or low-level keyboard routines.
The default key files (@.ssh/id_rsa@, @.ssh/id_dsa@ and @.ssh/identity@) should be handled automatically. If you have a key with a different name, you can add it with @ssh-add path/to/my_key@
<p class="attention">Make sure that you're using the default OS X ssh-add command and not one installed by macports or some other external source.</p>
When you first try to use the key you will be prompted to enter your passphrase:
!/images/SecurityAgent.jpg(Keychain prompt)!
If you choose to save the passphrase with your keychain, you won't have to enter it again. Instead you'll simply need to unlock your keychain.
<p class="attention">This section was written with help from "this guide":http://www.dribin.org/dave/blog/archives/2007/11/28/ssh_agent_leopard/. If you would like to use more paranoid keychain settings like locking after sleep, check out "this guide":http://www.dribin.org/dave/blog/archives/2007/11/28/securing_ssh_agent/.</p>
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