Radium Box provides seamless service as RA (Registration Authority) to buy Digital Signatur Certificates for MCA ROC filing, e tendering, e-procurement, Income Tax efiling, Foreign Trade, EPFO, Trademark, etc. Buy Digital Signature online from Radium Box. 3 Simple steps to get Digital Signature Certificates. Find out how to create and how it works. Digital Signature is a process that guarantees that the contents of a message have not been altered in transit. When you, the server, digitally sign a document, you add a one-way hash (encryption) of the message content using your public and private key pair.