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I've started using SSH keys instead of passwords just recently (thanks to GitHub, of course), so please keep in mind that I'm pretty new to this whole concept. Currently my keys simply lay in ~/.ssh, but I'm not sure if this is a good practice. E.g. if I have multiple machines, I'd need to duplicate private keys, which I think is undesirable. Also, if my HDD go kaput, I'll lose my private key, which (I guess) is undesirable as well.

So, what are best practices on storing SSH keys securely, conveniently, and reliably?

Seems like using a smartcard is an option (see Smartcards for storing gpg/ssh keys (Linux) - what do I need?), is this the best one?

Update: The reason for the question was that many services (like GitHub, AWS EC2) provide guides how to set up SSH keys for using the service, but little or no background info (like, what to do if you already have some key generated by ssh-keygen [1], what are recommended security measures). And it's unclear whether that info is in fact unimportant, or you're expected to know it ‘by default’.

To sum up answers up to this point (but please read them, and if you have something to add—please do): seems like in this case it's fine if you just leave your private keys in ~/.ssh, as long as you keep them from other people; but make sure that you have another way to access the service to upload or generate a new key if you lose one (which is normally the case).

[1] GitHub, as it turned out, provides some help on how to manage multiple keys.

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4 Answers 4

up vote 13 down vote accepted

E.g. if I have multiple machines, I'd need to duplicate private keys, which I think is undesirable.

No, actually you don't. If you have multiple machines, you just create a separate private key on each one. For each private key, just upload the corresponding public key to GitHub using the same process.

Also, if my HDD go kaput, I'll lose my private key, which (I guess) is undesirable as well.

Not really; if you lose your private key, just generate a new one and upload the corresponding public key.

For what it's worth, you're right that duplicating a private key is highly undesirable. Ideally, a private key should be generated in one file (~/.ssh/id_rsa for example) and should never leave that file - that is, it should never be copied, moved, and especially not transferred over a network. (e.g. I exclude them from backups) Because of the nature of asymmetric authentication protocols, you only need to worry about keeping your private key out of the hands of others. If you go a bit overboard and you lose track of it yourself, it's generally not a big deal. (This is not to be confused with asymmetric encryption private keys, e.g. GPG keys, which you probably want to hold on to.)

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1  
This only works if you have some other method of accessing the servers that that private key provides access to. You can upload the new public key only if you have that backup access. –  TREE Aug 16 '11 at 20:08
    
@TREE: right, but in my experience it's exceptionally rare to find a server that doesn't provide some alternative method of access (or at least of adding an additional public key without going through SSH). –  David Z Aug 16 '11 at 20:11
    
Thanks, that clears things up a lot. Really, losing private SSH key doesn't look like an issue, since for all services I'm using there always seems to be another way to access a service to upload a new one. –  Anton Strogonoff Aug 16 '11 at 20:58

I would add that ~/.ssh/ is readable by your browser if you are using the same user account to run both.

Try it! Point your browser to your private key in your home directory. It's fun.

So I would recommend storing ssh-keys in the home directory of another user account.

a word on passphrase protecting keys

  • These days, cracking non-randomized passwords is super fast . Check out hash cat
    • ( Though random and long 12+ char passwords still take reasonably long to brute force)
    • So AES encrypted ssh keys are uncrackable for the foreseeable future as long as you use good long passphrases. See github recommendations
  • So some website can guess-grab your key w/o JavaScript . And then brute-force the key offline.
  • And browsers can look into your Clipboard w/ JS too. So copy-pasting very long passphrases also puts you at risk from the more sophisticated javascript attacks.

look_at_keys.html

 9 <HTML>
10 <HEAD>
11 <TITLE>look at keys</TITLE>
12 </HEAD>
13 <FRAMESET cols="20%, 80%">
14   <FRAMESET rows="100, 200">
15       <FRAME src="/Users/yourname/.ssh/stuff.pem">
16       <FRAME src="blah.html">
17   </FRAMESET>
18   <FRAME src="contents_of_frame3.html">
19 </FRAMESET>
20 </HTML>
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4  
To be clear, just because the browser can read your private key that doesn't mean a website running in the browser can. –  Ajedi32 Aug 27 '13 at 18:55
    
But, if you inject a process in browser's process. Then you can take control of browser as well. So this argument is perfectly valid. –  BigSack Apr 5 at 10:16

I have a tar file which has my user dir setup (.bashrc, .ssh/ and other config files) that I keep in a safe place. When I get a new shell account anywhere, I unzip the tar file into it.

You should only put your private keys onto servers you trust, otherwise you should create a new private key on the server just for that server, and allow it access to things you want it to have access to.

Personally, I'm comfortable just copying my .ssh/ stuff around everywhere (it also means by regular ssh key gets ssh access instantly, since it's already in the authorized_keys file).

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I guess, having encrypted ~/.ssh hanging around on a usb stick would save from the need to generate and upload new key in case of the hardware failure. However, since there're very few servers that I use SSH keys to access (and very few machines I connect from), generating new keys won't cause much overhead. –  Anton Strogonoff Aug 16 '11 at 21:35
    
It's horses for courses and depends on why you use the keys. I don't see a problem copying an ssh private key over an already encrypted SSH link. But if you don't trust the target machine and don't know who has root access, you shouldn't put anything on the server you can't afford to lose. –  EightBitTony Aug 16 '11 at 22:12

I would recommend storing private keys:

  • offline (not in the cloud)
  • in more than one place
  • apart from anything it's related to, e.g. a key for your encrypted data, store it in a separate place from the data

I'd say, the best place would be:

  • an external hard drive
  • a flash key
  • a computer not plugged into the internet

Even better, just print it out, and put it in a fire proof safe.

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