DIGITAL SIGNATURE ALGORITHM 

Digital Signature

A digital signature is a mathematical technique which validates the authenticity and integrity of a message, software or digital documents.
 

It allows us to verify the author name, date and time of signatures, and authenticate the message contents. 

The digital signature offers far more inherent security and is intended to solve the problem of tampering and impersonation (Intentionally copying another person's characteristics) in digital communications.

The important reason to implement digital signature to communication is:

• Authentication
• Non-repudiation
• Integrity

Authentication

Authentication is a process which verifies the identity of a user who wants to access the system. In the digital signature, authentication helps to authenticate the sources of messages.

Non-repudiation

Non-repudiation means assurance of something that cannot be denied. It ensures that someone to a contract or communication cannot later deny the authenticity of their signature on a document or in a file or the sending of a message that they originated.

Integrity

Integrity ensures that the message is real, accurate and safeguards from unauthorized user modification during the transmission.

Algorithms in Digital Signature

A digital signature consists of three algorithms:

1. Key generation algorithm

The key generation algorithm selects a private key randomly from a set of possible private keys. This algorithm provides the private key and its corresponding public key.

2. Signing algorithm

A signing algorithm produces a signature for the document.

3. Signature verifying algorithm

A signature verifying algorithm either accepts or rejects the document's authenticity.

How digital signatures work

Digital signatures are created and verified by using public key cryptography, also known as asymmetric cryptography. 

By the use of a public key algorithm, such as RSA, one can generate two keys that are mathematically linked- one is a private key, and another is a public key.

The user who is creating the digital signature uses their own private key to encrypt the signature-related document. 

There is only one way to decrypt that document is with the use of the signer's public key.

This technology requires all the parties to trust that the individual who creates the signature has been able to keep their private key secret. 

If someone has access to the signer's private key, there is a possibility that they could create fraudulent signatures in the name of the private key holder.