Hi Lance,
Yes that will be the case, actually you can even store them in both keystore and truststore but it is bad practice.
I bit confused if an outside entity has shared they’re private keys they could be compromising they’re system. If you mean that you have been provided with a private key to enable SSH connections to IS from outside place them in a keystore with java keytool then import it to the IS.
You should be able to see it in the IS next step is to enable a HTTPS port in the IS that will use that private key to establish the SSH connection.
By the way if this revorse invoke server you should be getting CA certificates to avoid man in the middle attacks, anyone who gets access to you’re certificate/key will be able to trick the client by impersionating you’re server the Certificate Authority makes sure that the CA certificate is linked to you’re machine network address or IP.
On the other hand if you will be the client then you (might) need the public certificate of the server you are comunicating and that is deployed on Certificates at the IS admin.
Can you open the certificate on the notepad does it contains KEY or CERTIFICA with begin end tags? What is the extension?
rmg highly appreciate a compliment from a wM guru 
Regards and hope it helps.
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