A Zero-knowledge proof (a.k.a. zero-knowledge protocol) in the field of cryptography is a method by which one person (or side) proves the other person(or side) that he (or it) has a particular piece of information, without revealing any other part of the same information he(or it) is carrying.
Suppose Romeo and Juliet want to check the authenticity using secret number "9". After taking the deck of cards, Romeo puts his hands (with cards in hand) inside the handbag and starts to remove cards one by one until he reaches the 9th card. He takes this 9th card out of the handbag and shows it to himself and Juliet.
Without making any change in the the original sequence of cards, Romeo then keeps the cards on the deck back again.
It is the turn of Juliet now. She keeps a track of counting of cards holding the deck of cards and puts her hands in the handbag hidden from Romeo. If she knows that the secret number is '9' then she should keep removing the cards out until the 9th card is reached and show the exact same card which Romeo did.
Now the authenticity verification says that If Romeo and Juliet had drawn different cards assuming that they both knew the secret number '9', then the exact same number of cards have not been drawn by them.
To even a single transaction in business, TRUST is elementary . For making any deal online or offline in the real world, knowing the party with who the business is done and if that party will do the job or not is of vital importance. The major problem is in the process, privacy may be compromised. So, for the purpose of decision-making about trusting the other party, having knowledge about the category(good or bad) of persons they belong to is necessary. In short, their personal information has to be gained.
