Upload SSH Private Key to Upload Center

Hello,

I am have some difficulty uploading my SSH Private Key to the Upload Center under Administration. I had no problem generating the key using Putty, as I have done this before.

I am downloading the private key directly from the Putty Key Generator to my desktop. It is file type .ppk

When I attempt to Upload the SSH Private Key it gives me an error "The file is not a valid SSH Private Key file." So my question is what file types are valid for an SSH Private Key? I can't find any documentation in Oracle docs.

Thanks!