I can't connect to server instance using SSH key from Cygwin. I found, that I can't change ssh key file permission.
WARNING: UNPROTECTED PRIVATE KEY FILE!
To resolve this copy your SSH key to /tmp/mysshkey:
mkdir /tmp/fermin cp ~/.ssh/id_rsa /tmp/fermin chmod 600 /tmp/fermin/id_rsa ssh -l fermin -i /tmp/fermin/id_rsa localhost