@erobinson When you get a chance, please introduce yourself here. I'd also encourage you to add a real picture as your avatar because it helps build community!
https://github.com/getodk/central/tree/master/files/dkim doesn't have a rsa.private
directory and when I run openssl genrsa -out rsa.private 1024
it creates a file, not a directory.
Are you running a recent copy of Central? From your central directory, run git describe --tags
and report back what it says.