A digital signature is one of the best methods in the security of message in digital data communication. Technically the digital signature is inherited from the public key cryptography.
The public key digital signature provides data integrity and authenticity. The numeric name was also able to offer nonrepudiation which means that the identity of the sender is well known, so s/he didn’t dot chance to claim that the information is not sent from his/her device or ID, this feature enable privacy much more enhanced.
The digital signature can perform the same purpose as handwritten hard copy Signature, but handwritten signature can be smooth to counterfeit, but digital signature is advance to handwritten signature it is nearly impossible to copy the same name more than one plus it is attested to the information along to identity of the signer.
In some sense, In older days digital signature is used as a medium of encryption and decryption. The message merely is signed with the private key and decrypt with public key if it matched then the signed document is genuine, but it has some demerits the document size is more the communication process is slow and many more now in new digital signature the concept of hash function and message digest arrive.
An improvement on the older schema the addition of hash function is applied. A hash function is a one-way function that takes a million bits of input and produces a fixed length of output; let’s say in 64 bit then if a bit change in original information then the entire different result is provided in production which secures the originality of the information
From The original data and the strong hash function, the message digest is generated. The message digest is the process of generation of a fixed length of data items. (Any significant change in data cause an entire shift in summary) The digest and private key are used to create a signature and transmitted the name along the information. As the hash function, there is no chance of taking someone’s signature form any document and applied for another. The slight change may cause failure in the verification process of the digital signature.
As long as the hash function is used, there is no way to take someone’s signature from one document and attach it to another or to alter a signed message in any way. A single change in a signed certificate will cause the digital signature verification process to fail.