Recently I tried setting up Workflow Manager 1.0 on a new Server 2012 R2 server. The problems were inconsistent and unspecific in the error message--I tried several URIs that all matched the server, but when using http:// I would get a 404 error and with https I would get a "the root certificate authority is not trusted" even after using a domain CA and spending a lot of time to try to match up the correct URIs in the certificate and to manually register the domain CA with Sharepoint's internal list of trusted roots.
The trick is to install updates to Workflow Manager that are not part of the web platform installer, as I learned from Rob Hardy's blog. After installing CU 2 for Service Bus and Workflow Manager, I was able to register the Sharepoint Workflow Service with no problems using HTTP.
I am not going to try HTTPS again right now, after getting things to finally work.