Force SSL for encryption

I found this code in the guide I’m using:
define ('FORCE_SSL_LOGIN' true);
Apperently it’s dropped into wp-config to force SSL to encrypt usernames and passwords. I don’t know if matters were confused but my host says it will do nothing for me unless I obtain a cert.
The guide however mentions nothing about the cert.

Can anyone confirm whether the code will
1) do what it promises
2) break something
3) and whether an additional cert becomes mandatory

The reason for this inquiry is that I don’t want to encrypt login credential with a plugin. And I don’t believe a cert is necessary.