Zero-Knowledge Proofs (zk-Proofs) were known long before blockchain technology emerged, but with distributed ledgers, a whole new set of possible use-cases came around.
A protocol is a standard composed of a set of rules and conventions used for a given purpose. Let us take a look at what some of the conventions and rules for a blockchain look like.
Directed Acyclic Graphs
The term DAG stands for Directed Acyclic Graph. The structure on the far left of the image below is a simple graph made up of nodes and edges connecting the nodes. In a directed graph each connection has a direction, indicated by the arrows. A directed acyclic graph (DAG) does not allow cyclic relationships of nodes like the one you can see in the bottom part of the directed graph in the middle.
A hash function is a mathematical function with a few special properties, but like any other function, it does one job. The hash function takes an input and produces an output (also called hash value, hash digest or a hash).
The UTXO Model
When you think about how your bank does the accounting for your bank account, it is pretty intuitive. You hold a certain amount of funds in your account, which has an account number. If you receive an incoming transaction, the amount is added to your balance. If you spend money, then the amount you spend gets subtracted from your balance. With cryptocurrencies, the accounting works a little different.
According to Wikipedia, “The nothing to hide argument states that government surveillance programs do not threaten privacy unless they uncover illegal activities and that if they do uncover illegal activities, the person committing these activities does not have the right to keep them private. Hence, a person who favours this argument may state “I’ve got nothing to hide” and therefore does not express opposition to government surveillance. An individual using this argument may say that a person should not worry about government or surveillance if he/she has “nothing to hide.”