Digital Signature

Digital signature:-

The most important development from the work on public-key cryptography is the digital signature. Message authentication protects two parties who exchange messages from any third party. However, it does not protect the two parties against each other. A digital signature is analogous to the handwritten signature, and provides a set of security capabilities that would be difficult to implement in any other way. It must have the following properties:

• It must verify the author and the date and time of the signature
• It must to authenticate the contents at the time of the signature 
• It must be verifiable by third parties, to resolve disputes

Thus, the digital signature function includes the authentication function. A variety of approaches has been proposed for the digital signature function. 

These approaches fall into two categories: direct and arbitrated.

• Operation is similar to that of the MAC.
• The hash value of a message is encrypted with a user’s private key.
• Anyone who knows the user’s public key can verify the integrity of the message.
• An attacker who wishes to alter the message would need to know the user’s private key.
• Implications of digital signatures go beyond  just message authentication.