I already created an ssh key for myself sometime in the past. I don't remember "how many bits" it is. How can I tell?

I'm wondering because I'm using hosting at nearlyfreespeech.net and their faq says:

Can I configure my ssh connection to use a public key?

... we will not install keys that have a length less than 1536 bits ... We prefer that you use a key at least 2048 bits in length, and if you are generating a new key, the recommended length is 4096 bits.

[palvarez@oizon ~]$ ssh-keygen -l -f ~/.ssh/id_rsa.pub
2048 2e:8c:fd:aa:9f:95:86:9e:b0:d2:a6:1a:7e:d3:3e:74 .ssh/id_rsa.pub (RSA)

2048 bits.


  -l          Show the fingerprint of the key file.
  -f filename Filename of the key file.
  • 1
    Like your 2nd half, maybe should have read both halfs before opening up the manpage :-) – Puggan Se Oct 11 '13 at 12:00
  • 7
    Why read the manpage when you have SO!? No… but really… sometimes the important bits are hidden in overly complex explanations for obscure flags, etc. Also I wouldn't have assumed ssh-keygen could be used to check an already generated file. – Benji Jun 21 '18 at 8:01
  • 2
    Just to add, it helps to remember for -l as "length of fingerprint/signature" or for both '-lf' as 'length of signature for file'. Hope that helps others as it helped me. – icasimpan Nov 27 '19 at 15:51

You can also see a visual ASCII art representation of the key.

ssh-keygen -l -v -f ~/.ssh/id_rsa.pub
3072 SHA256:3v8ZClFzsdN3ihY8U6TVWltcXheSz+DX40PLf2uSRwQ dobbs@snow (RSA)
+---[RSA 3072]----+
|             o*+*|
|           . E.=B|
|            X OoO|
|           . O.@+|
|        S . o B o|
|       . . o   * |
|        . o   + o|
|           o + =o|
|            o.*.o|

3072 bits.


     -l      Show fingerprint of specified public key file.
             If combined with -v, a visual ASCII art representation of the
             key is supplied with the fingerprint.

     -f filename
             Specifies the filename of the key file.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.