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2.4 Type of blockchain

Blockchain can be classified into two categories public vs private and permissionless vs permissioned.

A private blockchain means that there is control over the user access to the network and the information.
It is a network-based on “invitation-only” and is governed by a single entity, which makes it exclude
one of the main defining features of blockchain – decentralization. On occasion, it might allow for
different levels of permissions for the users. In this case, the access can be partially or fully restricted,
and information can be encrypted for confidentiality. The participants in the networks must have
permission to read, write or verify the data on the blockchain. It is considered less secure than a public
blockchain. The public blockchain is considered as a transparent and open ledger all the nodes and
the transactions are public. Given that public ledger is distributed and decentralized, the information
is then encrypted and stored on multiple devices which increase the level of security of the public
blockchain. The public blockchain is considered to be immutable, which means that once the data have
been verified it cannot be altered.

The permissionless vs permissioned type of blockchain is associated with the permission level given
to the participant to read, write and audit, as well as to commit to the network. The entities of the
permissionless blockchain that write data are not known. In a permissioned blockchain, a limited set
of known entities is authorized to write in the system. 26

A combination of the different types of blockchain solutions is composed of blockchain architecture
options. These options are presented in Figure 3.

Figure 3: Blockchain architecture options and differences 27

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