What are the essential points of distinction between three separate classes of the same blockchain technology -- public, private, and consortium?
Bitcoin is the original ‘blockchain.’ Though the word itself never appears in the whitepaper, the vision was for a truly peer-to-peer cash system for the internet age. The ‘blockchain’ results from the pursuit of that end goal.
Bitcoin brings together several technologies, allowing scarce PoW (proof of work) network tokens to become a type of digital cash.
It is often forgotten that the blockchain is not the end in itself. It serves the system. The intention was never to create a ‘blockchain;’ the intention was to create a type of digital cash.
In any case, and for whatever reason, the dialogue has shifted focus. The blockchain is the thing. It is a technology gaining increasing attention. Experimentation is accelerating, and the vernacular is expanding.
Now we have different types of blockchains.
What Is a Blockchain Generally?
This is contentious. It is a new field and opinions differ greatly. In very general terms, it is a tamper-resistant database, distributed over a network, that achieves consensus without a single point of control.
This definition is kept deliberately broad to satisfy all sides of the debate.
Bitcoin is both the original blockchain and the original public blockchain.
Public blockchains are best understood according to their key characteristics. The most important characteristic is that the database, representing the list of all transactions since the inception of the database, is publicly available and viewable by anyone, anywhere. Further, participation in the network, and the ability to submit transactions, is completely open.
The only requirement is possession of the network token. This is the sole access point. If you have the token, you can use the network.
Public blockchains are a common, public good. They require volunteers to secure entries, either through PoW, PoS or any other consensus method. Ability to participate in consensus and resolution of transactions is completely open to any participant.
A public blockchain is, therefore, a completely transparent database of transactions on an open network. Anyone is free to submit transactions to the network, and participate in the ongoing security of the network.
Private blockchains are, essentially, the inverse of public blockchains in all key attributes. As a result they are understood by some as simply a newer type of database structure that cannot really be classified as a blockchain at all.
Whether global, public access is required for classification as a blockchain is an ongoing and contentious debate. In many ways it is merely a matter of semantics.
So called private blockchains do not have their complete history of transactions available to anyone. There are gatekeepers. They control who can see what transactions, and when they can see them.
Who can participate and submit transactions, and who acts to secure the database, are all the subject of governance rules, which can involve central, semi-central or loose management approaches.
Ultimately, private blockchain is a catch-all term for anything that is not completely public. There is broad flexibility for governance and management within it. Private blockchains can even ultimately resolve to a public blockchain.
The distinction of a consortium blockchain centers primarily on the method of consensus. Here, the consortium itself decides which nodes on the network will have the authority to sign (approve) which transactions.
In terms of read access to the database, this can be completely public, private or anywhere on the spectrum. The available variations and permutations within this model are enormous.
The route taken by any consortium as to read access, write access, and consensus, will ultimately depend on the goals of the consortium and the specific use case for the blockchain database.
Blockchain is an emerging field. The technology itself is very new. Our understanding is superficial.
Fully decentralized public blockchains, fully private blockchains and consortium blockchains all have potential use cases. There are a myriad of permutations in between. They are not completely distinct and separate, but are best understood as a spectrum.
Where each type of blockchain finds ultimate use depends on the goals of the system and its creators.