Digital signature requirement: higher assurance certificates required for electronic invoices, with prior notification and multi year record retention. Assessees must use Class 2 or Class 3 Digital Signature Certificates issued in India and notify jurisdictional officers of designated users and certificate details; maintain separate electronic records by factory or registration; produce electronically readable records and invoices on official request; provide verified printouts during enquiries or audits; and preserve backups with retention for a multi year period after the relevant financial year.