Din -3

I want to obtain Digital signature certificate for filling DIR-3 form for applying DIN and incorporating a new company Now my ques is.. there are 7-8 certying authorities who issues DSC..and all of them are charging diff. charges..So I'm confuse which authority is best in terms of evrything...price,support,etc also if my purpose is to format a company, then which category i shud go for..i mean..to choose sign facility DSC or Sign & Encrypt facility DSC. What is the diffrence between the two and what are its uses..under wht cicumsatnces sign & encrypt is used. thxs...