How to set 600 permission on a .pem file in w10?

I got in. For posterity, here's what was happening. It was a two-part problem.

  1. I am using Git Bash. On an ls -al command, the permissions were shown as rw-r--r--. When viewed in Windows Properties, they were set correctly.

  2. The username on the remote box was not properly set up for ssh

To discover this, I logged in using tried from my Mac, setting the permissions in a linux-style. There I found that the username was not set up. Then I went back to windows and tried again, despite the permissions appearing wrong in Git bash... and it worked.