Asymmetric Cryptography uses the concept of Public Key and Private Key, known as Key Pair. They are mathematically related so that the Public Key would always verify the output of Private Key.

The process is something like, the owner has available to him both Public Key and Private Key. But his Public Key is available to anyone who needs it, but he keeps his private key to himself.

To put a digital signature on a document, the Hashing process is used which employs Hash Algorithm. The Hashing process crunches down the data into just few lines, which is called a Message Digest. The Hash algorithm consistently produces the same result, every time it is applied.

The owner with the help of his Private Key then encrypts this Message Digest. The result is the Digital Signature, which is appended to a document. The recipient in possession of Public Key can decrypt the resulting Digital Signature, changing back into the Message Digest.

If the decryption works, it proves the owner signed the document. It can further be verified that the document has not been tampered with, by hashing the document data into Message Digest. Which can be compared with the Message Digest created when the signature was decrypted.

So basically the steps involved in creation of Digital Signature can be summarized as follows:

• The hash algorithm is applied on the Document to generate Message Digest.
• The hash code is encrypted with the sender’s private key, producing the Digital Signature.
• Lastly, the Digital Signature is appended to the Document to be sent to the recipient.