I have added an SSH credential to Jenkins.
Unfortunately, I have forgotten the SSH passphrase and would now like to obtain it from Jenkins\' credential archive, which is
Yes you can get it back. It is AES encrypted and you have to do some things before like searching for the passphrase. Have a look into the Secret class.
But you have look, there are already some scripts out there:
https://github.com/tweksteen/jenkins-decrypt
https://gist.github.com/menski/8f9980999ed43246b9b2
More information and a way to do it with java, can you find here:
What password encryption Jenkins is using?