What is Digital Signature?
A digital signature is an example of using encryption techniques to provide authentication services in electronics commerce applications. Like a handwritten signature, a digital signature is a means of associating a mark unique to an individual with a body of text.
A digital signature consists of a string of symbols. If a person’s digital signature were always the same for each message, then one could easily counterfeit it by simply copying the string of symbols.
Thus, signatures must be different for each use. This can be achieved by making each digital signature a function of the message that it is signing, together with a time stamp. To be unique to each signer and counterfeit-proof, each digital signature must also depends on some secret number that is unique to the signer.
Thus, in general, a counterfeit-proof digital signature must depends on the message and a unique secret number of the signer.
The verifier of the signature, however, should not need to know any secret number. Public key techniques are the best means of creating digital signatures with these properties.