You can now enable official SSL certificate with your custom domain. This future is currently in beta, but every blogger can use it via draft.blogger.com.
- First go to draft.blogger.com
- Go to setting, then basic and choose yes in HTTPS availability.
- Now go back to your main blogger dashboard(blogger.com).
- Now wait for few minutes, and you can see same option there as well, so choose yes in both option. I enable it in just 2 minute, but it may take long time for your blog, because they register your SSL certificate automatically for your custom domain.