How can I encrypt the login process without using SSL?
So far, the only way that I've found to encrypt user login without SSL is the Encrypt Submissions Module (https://www.drupal.org/project/encrypt_submissions)

It uses the jCryption library (http://www.jcryption.org/) to encrypt the username and password that drupal offers up in clear text otherwise. Fairly straightforward to set up. The only server requirement is bcmath php module which most servers have anyway.

I use Encrypt Submissions whenever I can't use SSL, not as a replacement. You may want to consider switching hosts if they don't allow SSL certs, they sound pretty backwards.