Different Types of Blockchains
Blockchains are either considered permissionless, permissioned or both. Permissionless blockchains allow any user to become the node of the network in a pseudo-anonymous way and there are no restrictions for the nodes on the network. Permissioned blockchains restrict access to certain nodes and can restrict the rights. The identities are thus known to the other users of that blockchain.
Public blockchains are permissionless. They are decentralized networks of computers accessible to anyone. These blockchains tend to be more secure due to the high number of nodes that validate transactions, but tend to be slower due to the higher traffic and large number of nodes required for consensus. Popular public blockchains include Bitcoin and Ethereum.
Private blockchains are permissioned. These are not open and have restrictions, often governed by one entity. Another way of saying this is that they are centralized. Because there are restrictions on the permissioned nodes, there are much less of them and therefore can be considered less secure. Due to the smaller number of nodes, however, they are often much faster. Many private blockchains are unknown to the public but a familiar one is the Hyperledger Network.
Consortium blockchains or federated blockchains are a type of permissioned blockchain that is governed by a central group of organizations rather than the one entity. Multiple members can collaborate on a decentralized private network without worry that one central entity is in control.
Hybrid blockchains are combination of public and private or permissioned and permissionless. They are controlled by a single organization, but with an oversight performed by the public blockchain. For example, organizers can set up the private, permission-based system alongside a public permissionless system, where some data can remain private and some can be public. The organizers can choose what aspect of the chain are private and permissioned and what are public and permissionless.
