Form 61A :registration & uploading problem

Under My account>Reporting Portal(Beta version)> New registration,
the portal asks to upload DSC in "cer" format. However, the DSC Management utility creates it in ".signature" format.
How is dsc to be created in that format?

Please provide a step by step guide to register in the portal (alongwith screenshot if possible).

Also, want to know how the information is to be filled & uploaded in Form 61A (i.e will it be done offline in a utility or online).