Unfortunately, the migration system does not easily allow to migrate a model across application rename.
Instead, you must export data from your database and import it back in django-simplesshkey.
The procedure below has been tested to upgrade from django-sshkey 2.5.0 to django-simplesshkey 1.0.0, with Django 1.11.
Export your existing SSH keys:
./manage.py dumpdata django_sshkey.userkey --natural-foreign --natural-primary --indent 4 > sshkeys.json
Adapt the dump for the new model name:
sed -i -e 's/django_sshkey.userkey/simplesshkey.userkey/' sshkeys.json
Adapt your code to use django-simplesshkey. It should be as simple as replacing all occurrences of "django_sshkey" by "simplesshkey", but beware of other changes, for instance if you were using the "last_used" field.
Install version 0.0.0 of simplesshkey:
pip install django-simplesshkey==0.0.0
Remove "django_sshkey" from INSTALLED_APPS and add "simplesshkey" instead.
Run the initial migration for "simplesshkey":
./manage.py migrate simplesshkey
Import your data:
./manage.py loaddata sshkeys.json
Install the latest version of simplesshkey:
pip install --upgrade django-simplesshkey
Run the remaining migrations:
./manage.py migrate simplesshkey
This should be it!