What is A Digital Signature?

What is a digital signature?

Digital signature is a process of guarantees the content of the message  have not been altered (Changed) in transit.

The digital signature serves 3 purposes

• Authentication 
• Digital signature gives the receiver, reason to believe the message was created and send by the claimed sender


• Non-repudiation
• With a digital signature, the sender cannot deny having sent the message later on


• Integrity
• A digital signature ensures that message was not altered in transit

With digital Signature, you are trying to prove that a document signed by you came from you. To do that you need to something that only you have. It is your private key

Simply a digital signature is a hash of data that is subsequently encrypted with signers private key.

Signer

• First signer generate key pair and keep private key safe(everyone knows the public key)
• And then get the data and use a hashing algorithm and get the hash of the data
• Then get the hash of data and encrypt using signers private key
• Finally, send the encrypted documented and normal document (digitally signed document)to the receiver

Verifier

• Verifier receives two files encrypted document and normal document
• First, get the encrypted document and decrypt it using Signers public key
• we can get the hash of the document after decrypting it.
• Then get the normal document and use the same hash algorithm and get the hash of the normal document
• Compare the two hash values 

If the two hash values matched the signature is considered as valid.