How to list keys added to ssh-agent with ssh-add?

How and where can I check what keys have been added with ssh-add to my ssh-agent?

Asked By: Patryk

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Use ssh-add -l to list them by fingerprint.

$ ssh-add -l
2048 72:...:eb /home/gert/.ssh/mykey (RSA)

Or ssh-add -L to get the full key in OpenSSH format.

$ ssh-add -L
ssh-rsa AAAAB3NzaC1yc[...]B63SQ== /home/gert/.ssh/id_rsa

The latter format is the same as you would put them in a ~/.ssh/authorized_keys file.

Answered By: gertvdijk

Surprisingly the MacOS version of ssh-add at some point stopped showing the filename’s as with the Linux variant. I wrote this script which does the same for fingerprints that have a corresponding file in ~/.ssh/.

I call the function ssh-add_wf, wf = with file. The details on the function are below:

$ type ssh-add_wf
ssh-add_wf is a function
ssh-add_wf ()
{
    while read -r line; do
        for file in ~/.ssh/*.pub;
        do
            printf "%s %sn" "$(ssh-keygen -lf "$file" | awk '{$1=""}1')" "$file";
        done | column -t | grep --color=auto "$line" || echo "$line";
    done < <(ssh-add -l | awk '{print $2}')
}

Example

$  ssh-add_wf
 SHA256:mwvSCr2CXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX  myuser@mydom.lan  (RSA)  /Users/myuser/.ssh/ssh_myuser@mydom.lan_id_rsa.pub
 SHA256:qInIrnKcXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX  myuser@mydom.com  (RSA)  /Users/myuser/.ssh/github_myuser@mydom.com_id_rsa.pub
 SHA256:tX+AAJA0XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 SHA256:EyNkhTLQXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX  myuser@mydom.com  (RSA)  /Users/myuser/.ssh/ssh_myuser@mydom.com_id_rsa.pub
 SHA256:KKKVwtvFXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 SHA256:tr0hZP52XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Above, any keys within ssh-add‘s output that match to a file in ~/.ssh/ directory will include the file’s name in the output in the 4th column. Any keys that do not will have that column empty. In this output we have 3 keys which have files that match.

Mechanics of function

The script uses 2 loops. The outside loop is a while which takes the output of ssh-add. This output is all the fingerprints of SSH keys loaded into ssh-agent.

The interior loop is a for loop which goes thru the contents of all the files matching this pattern, ~/.ssh/*.pub. For each file we interrogate it with ssh-keygen -lf <file> and then drop the first column of this output:

…before…

4096 SHA256:mwvSCr2CXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX myuser@mydom.lan

…after…

SHA256:mwvSCr2CXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX myuser@mydom.lan

This string is then printed along with the name of the file:

printf “%s %sn” “$(ssh-keygen -lf “$file” | awk ‘{$1=””}1’)” “$file”

At the end of the execution of this loop is the following:

| column -t | grep “$line” || echo “$line”

This formats the output so that it’s column formatted (column -t).

At this point we look at this output for the fingerprint from ssh-add via the grep "$line". If a match is found we print our printf output, otherwise we fall back to just printing the original fingerprint from ssh-add, $line.

References

Answered By: slm
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