Compare keys in ssh-agent with the pub keys

I like having one key per environment I connect to, including each forge I push code to. It's a good security measure.

So for instance, I have one key for Github, one for Gitlab, one for Azure Dev Ops and so on. To make effortlessly with ssh authentication, which is my preferred transport for git as well as logging onto servers, I have them all in my ssh-agent:

$ ssh-add -l
3072 SHA256:AEFWADFSFADSasdfasfdfasfasd+adsfafwwwwqasd torstein@bar (RSA)
256 SHA256:IrN6COBlIUXdQWDERWQQWOobU8hnkIj6s+asdfadfsd torstein@foo (ED25519)
256 SHA256:rmFWhSDQEFWRSAFDYHJSFSAasASDFFASDFQQWEWW/9s torstein@mithrandir (ED25519)

The problem is only, from which key in ~/.ssh does this come? The contents of a ~/.ssh/id_ed25519.pub is completely different:

$ cat ~/.ssh/id_ed25519.pub
ssh-ed25519 AAASDFASDFASDFAFSDqq/adsfadfs/adsfkjw torstein@some.other

Turns out, you easily see hte SHA256 fingerprint of your .pub file with:

$ ssh-keygen -lf 
$ ssh-keygen -lf ~/.ssh/id_ed25519.pub
256 SHA256:IrN6COBlIUXADUQSXkROobU8hnasdfQ+WQAS torstein@some.other (ED25519)

With that, it's easy to see which key pair in ~/.ssh have been added to ssh-agent:

$ ssh-add -l |
  awk '{print $2}' |
  while read sig; do
    find ~/.ssh -name "*.pub" |
      while read key; do
        echo -n $key ' ';
        ssh-keygen -lf ~/.ssh/$(basename "$key" .pub)
      done | grep $sig ;
  done

Happy hacking!

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