4 ms·

Seeing a key with substring of "Tyr" as the username and that substring of my key matching scared me a bit. If you want to check how many bits your key is, use

• timdorr 11y ago
  Most people will want to run this verbatim: ssh-keygen -l -f ~/.ssh/id_rsa.pub You'll get an output like so: ⚡~ $ ssh-keygen -l -f ~/.ssh/id_rsa.pub 2048 f6:2d:94:54:c0:96:18:64:24:fb:c2:ad:ed:6a:1d:68 timdorr@Pixelicious.local (RSA)
  • tyrel 11y ago
    True, this will be default if you don't namespace your keys and use ssh config files like I do, I should have just said that.
  • Killswitch 11y ago
    4096 63:f2:23:00:c9:0d:07:3b:6d:ad:4d:a9:98:32:f5:25 ***@*** (RSA) Am I good?
    • wwwhizz 11y ago
      Your key is 4096 bits, you're good.
  • _lce0 11y ago
    how much safe are we, with a 2048 bits key? is this something we should be upgrading (like to 4096) in the near future?
    • mbesto 11y ago
      I don't have a qualified answer but given he says it would take 24 minutes to crack a 256bit key and 3 days to do a 512bit, I would extrapolate (given exponentially difficulty as you add more bits) to roughly: - 180x per doubling bit size would be - 512 doubled twice, would mean 3 days * 180 * 180 = 97,200 days I think you're safe.
      • knappe 11y ago
        On his/her admittedly subpar machine. Keep in mind that this will vary wildly for different hardware.
      • agwa 11y ago
        That's not how the math works. First, 2048 bits is not 512 bits doubled twice, but rather doubled 1536 times (512 doubled twice would be 514). If this were a symmetric cipher, you could stop here and conclude that a 2048 bit key was 2^1536 times stronger than a 512 bit key. However, RSA has diminishing returns on security as you increase the key length. The strength is determined by the complexity of the GNFS, the fastest known way of breaking RSA[1]. That tells us that breaking 256-bit RSA takes ~2^46 operations, 512-bit RSA takes ~2^63, 2048-bit RSA takes ~2^116, and 4096-bit RSA takes ~2^156. 2^116 is a lot of operations - they say the amount of energy required to break that would be nearly enough to boil all the water on earth. [1] http://crypto.stackexchange.com/questions/8687/security-strength-of-rsa-in-relation-with-the-modulus-size/8692#8692 http://crypto.stackexchange.com/questions/8687/security-stre...
        • therealmarv 11y ago
          great answer!
        • mikekchar 11y ago
          > they say the amount of energy required to break that would be nearly enough to boil all the water on earth. Not wanting to be alarmist, but what you're saying is that someone breaking my ssh key (which is 2048 bits) is the end of the world...
    • duskwuff 11y ago
      2048 is fine for the foreseeable future; it's the same key length used for most SSL certificates (including CAs!). Your next key upgrade should probably be to another key type entirely, most likely ED25519.
    • agwa 11y ago
      Not much point in upgrading from 2048 bit RSA to 4096 bit RSA. Instead, you should plan to upgrade to ed25519 keys when your client and servers support them - faster and better security than RSA.
      • therealmarv 11y ago
        Does anybody have a good (and easy!) guide how to do that on my Mac or Linux machine (client and server) ?
        • agwa 11y ago
          If you have experience with RSA key pairs, using ed25519 key pairs is easy. To generate a key pair just run: ssh-keygen -t ed25519 As with RSA, this command generates a public and private key file. Put the public key in the authorized_keys file on the server side. You'll need OpenSSH 6.4 on both the server and the client side. If you have an older version, I would not recommend upgrading outside of your operating system's normal upgrade channel because then you'll be responsible for security updates. Instead I would wait until your operating system has it.
        • toothbrush 11y ago
          It amounts to doing this: $ ssh-keygen -t ed25519 As usual, on the server, you do something like $ cat generated-key.pub >> ~you/.ssh/authorized_keys EDIT: sibling post was quicker off the bat. Oh well, that'll teach me to not refresh a tab :p
      • BlackFingolfin 11y ago
        Of course that is an "if" one should carefully think about -- e.g. it is OK if all you are using is OpenSSH at version 6.5 or later. (That can be a problem with many older boxes). But other than that, last I checked only SSH.NET and tinyssh supported ed25519 keys. Shameless plug for some more data on this: http://ssh-comparison.quendi.de/comparison.html http://ssh-comparison.quendi.de/comparison.html (yeah, that page could be a lot better -- pull requests are welcome)
  • philo23 11y ago
    There's probably a better way of doing it, but this should check all your public keys if you use more than one, assuming they're in ~/.ssh for file in $(ls ~/.ssh/*.pub); do ssh-keygen -lf $file; done
    • morganm 11y ago
      Not better, but could also be written as: find ~/.ssh -name '*.pub' | xargs ssh-keygen -lf Here's a simple bash function to check all your GitHub keys: function check_github_keys { username=$1 i=0 curl -sw "\n" "https://github.com/${username}.keys" | while IFS="\n" read -r line ; do tmp=`mktemp -t githubkey`; echo "$line" > $tmp res=$(ssh-keygen -lf $tmp) rm $tmp ((i=i+1)) echo "${username}.keys:${i} ${res/ $tmp/}" done } Invoke as: check_github_keys <username> I'm sure there's a better way to write that one though!
      • bobbyi_settv 11y ago
        Your initial "find" version would be better if it used print0 because it would avoid failing on files with spaces in their names: find ~/.ssh -name '*.pub' -print0 | xargs -0 ssh-keygen -lf
        • motoboi 11y ago
          This of course can be rewritten as find ~/.ssh -name \*.pub -exec ssh-keygen -lf {} \;
  • lobster_johnson 11y ago
    If you use ssh-agent, you can do: ssh-add -l to list all your registered keys.
• finicky 11y ago
  i had the same moment of panic and ended up removing old keys and regenerating my keys that are in use. i wish i'd seen this comment beforehand -_-