Digital Signature in BlockChain

A digital signature is equivalent of a handwritten signature but it is much more secure a handwritten signature can be faked.

A digital signature provides the recipient the following information:
      - The message was created by a known sender ( authentication).
      - The message cannot deny having sent the message (non-repudiation).
      - The message was not altered in transit (integrity)

How the digital signature is created and verified:

Alice has a document and wants to create a digital signature proofing to anyone that she is the owner of the document.

Alice creates a digital signature:
      - First she hash the data (document, piece of text, movie file, audio file, etc)
      - Next she uses her private key to encrypt the hash.
      - The encrypted hash is called the digital signature.

Bob wants Alice document. Alice sends the document and the digital signature.

Bob verifies the digital signature:
        - Bob decrypts the digital signature using Alice public key.
          The result is the hash value of the document (hash A)
        
        - Bob applies the same hash algorithm on the received document.
           The result is the hash value of the received document (hash B)
  
        - Bob compares both hash values (hash A, hash B)

         - If the hash values match it proofs that the document was not altered during transit and that the document is owned by Alice.

To Create a Digital Signature

 To verify a digital signature

Alice creating a digital signature:
ENC (H(p), priv keyalice) = sign

Bob verifying a digital signature:
DEC (sign, pub keyalice ) = hash val
H(p) = hash val

Examples :-