Access data of parent form when open a dialog using new Mscrm.CrmDialog

I am opening a web-resource using Mscrm.CrmDialog. When web-resource is opened i need values from different fields of entity form. 

I am unable to access the entity form.... How to access this entity form.

1 method is by passing values is query string. But the values are long, so query string breaks. Is this any other mwthod??? i.e. like access the entity form.

Thanks....

Waheed