restoring an OpenStack ssh public key

When a ssh private key is obtained from OpenStack via

openstack keypair create foobar > foobar.pem

the matching public key is stored in the OpenStack tenant. If it is later deleted with

openstack keypair delete foobar

it can be restored with

ssh-keygen -y  -f foobar.pem > foobar.pub
openstack keypair create --public-key foobar.pub foobar