1.3.public and private blockchain

                                     Public  and Private Blockchain

Public Blockchain 

A Public Blockchain, also known as a permissionless Blockchain, is open to all, and everyone can read as well as write over the data. In a public Blockchain, you don't need any authorization as you have open access to all the data. Moreover, if the Blockchain is public, the rules are very complicated, along with a complex consensus algorithm for better security. 

In this guide, we will discuss complex consensus algorithms in detail, along with Proof-of-Work and Proof Of-Stake. Miners use these algorithms to confirm transactions over the Blockchain. 

A public Blockchain has more complex consensus algorithms as compared to a private Blockchain because, in a private Blockchain, the permission is limited to a group of people who are accessing the network. So in a private Blockchain, you don't need miners to solve a complex problem wasting precious time because the data needs to be confirmed very quickly. 

In the case of a complex consensus algorithm, they are computationally more expensive to mine into a block. No one owns a public Blockchain; hence it has no central authority or a single person holding it. Even Satoshi, who started the white paper for bitcoin, transferred everything to the public in 2009. So all the public Blockchains are open, which means no one owns them, and you can read and write data over it. The Bitcoin Blockchain and Ethereum Blockchain are the best examples of public Blockchains. 

Private Blockchain 

Private Blockchain, as the name suggests, is for personal use. It can be used with your existing applications to make them even more secure. Such networks allow you to provide significant permissions like you can authorize the nodes connecting to the network. Nodes are nothing but different computers connected inside the peer-to-peer network running the Blockchain codes. 

In a private Blockchain, you can provide permissions as to who can read the data and who can transfer the data. You can even offer authorization in a way that only person A has the permission to transfer money, and person B can only view this data. 

Private Blockchain has less security as compared to a public Blockchain because, in a private Blockchain, we make it easily accessible to a certain trusted group of people and not millions. Also, if you are using a private Blockchain (like Hyperledger or Corda), then you can have the same kind of security as a public Blockchain or bitcoin, and one authorized node can be the arbitrator for any dispute. 

Now you know that the private Blockchain is for those who want to have more control over the Blockchain, who want to be the authority governing the Blockchain. A few good examples of a private Blockchain are RecordsKeeper Blockchain, Hyperledger, Corda, Quorum, etc.