A Digital Signature Certificate is similar to an hand written signature to establish the identity of the sender sending or filing the documents through internet and sender can not revoke or deny. It is a digital equivalent of a hand written signature. It ensures that no alterations are made to the data once the document has been digitally signed. A valid digital signature gives a recipient reason to believe that the message was created by a known sender, and that it was not altered in transit. Usually it is valid for 1 or 2 years after obtaining from digital signature providers and needs to be renewed.
It is used more extensively due to computerization of records and documents. The Information Technology Act, 2000 has given legal sanctity to digital signature thus, legally it has the same value as handwritten or signed signatures affixed to a document for verification. It provides authentication and integrity but does not provide confidentiality, data is sent as normal but acts like a normal signature we use on a letter.
Digital signature working
It uses asymmetric cryptosystems. Public-private keys are used to pass sensitive information. A digital signature works by creating a message digest which ranges from between a 128-bit and a 256-bit number which is generated by running the entire message through a hash algorithm. This generated number is then encrypted with the senders private key and added to the end of the message.
When the recipient receives the message they run the message through the same hash algorithm and generate the message digest number. They then decrypt the signature using the senders public key and providing the two numbers match they know the message is from who it says its from AND that is has not been modified.
