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diff --git a/_posts/2008-02-10-ssh-key-passphrases.textile b/_posts/2008-02-10-ssh-key-passphrases.textile new file mode 100644 index 0000000..c673220 --- /dev/null +++ b/_posts/2008-02-10-ssh-key-passphrases.textile @@ -0,0 +1,125 @@ +--- +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> |