Blockchain is always decentralized.

The statement that blockchain is always decentralized is an overgeneralization. While decentralization is a defining characteristic of public, permissionless blockchains like Bitcoin and Ethereum, it is not a mandatory feature for all types of blockchain implementations. There are different blockchain architectures with varying degrees of centralization. Private (Permissioned) Blockchains: These are controlled by a single organization. This central entity determines who can participate in the network, view the ledger, and validate transactions. This model is inherently centralized. Consortium (Federated) Blockchains: These are governed by a pre-selected group of organizations, not a single entity. While more decentralized than a private blockchain, they are still not fully decentralized like a public one, as control is restricted to the consortium members. Therefore, because centralized (private) and partially centralized (consortium) blockchains exist, the assertion that blockchain is always decentralized is false.

The statement is incorrect because of the absolute term "always." This fails to account for the diverse architectural models of blockchain technology. The existence of private and consortium blockchains, which are designed for specific enterprise use cases requiring control and privacy, directly contradicts this absolute claim.

1. MIT OpenCourseWare: In the "Blockchain and Money" course, it is explained that not all blockchains are decentralized. Private, permissioned blockchains are explicitly described as being centrally controlled.

Source: Gensler, G. (2018). 15.S12 Blockchain and Money, Fall 2018. Massachusetts Institute of Technology: MIT OpenCourseWare.

Reference: Lecture 5: Permissioned & Private Blockchains. The lecture contrasts permissionless systems (decentralized) with permissioned systems where a central gatekeeper or a consortium controls access and validation, making them centralized or partially centralized.

2. University of California, Berkeley Courseware: The "Blockchain Fundamentals" course distinguishes between different types of blockchains based on their governance and access models.

Source: UC Berkeley, CS 294-177: Cryptocurrency and Decentralized Systems.

Reference: Lecture materials on "Blockchain Architectures" differentiate between public (decentralized), consortium (partially decentralized), and private (centralized) blockchains, noting that private blockchains are managed by a single, trusted entity.

3. Peer-Reviewed Academic Publication: Academic surveys on blockchain technology consistently classify blockchains into different types, including centralized private blockchains.

Source: Zheng, Z., Xie, S., Dai, H. N., Chen, X., & Wang, H. (2018). Blockchain challenges and opportunities: A survey. International Journal of Web and Grid Services, 14(4), 352-375.

Reference: Section 2.2, "Types of Blockchains." The paper states, "Private blockchain is a blockchain where the write permissions are kept centralized to one organization."

DOI: https://doi.org/10.1504/IJWGS.2018.095647