Permissioned blockchain/ledger

A permissioned blockchain restricts who can validate transactions and, in many designs, who can even read the ledger, replacing open participation with a vetted list of approved operators. Where a public blockchain lets anyone run a node and compete for block rewards, a permissioned network hands that authority to a fixed or governance-approved set of organizations, often called validators.

Governance can sit with a single company, sometimes labeled a private blockchain, or with a consortium of independent entities that jointly decide who joins and how blocks get confirmed. The XRP Ledger illustrates a widely cited hybrid case: the software and transaction history are public, but each server operator trusts a configurable "Unique Node List" of validators, built from recommended lists published by the XRP Ledger Foundation and Ripple, which have historically included operators such as MIT, Microsoft, and CGI alongside dozens of independent businesses, universities, and hobbyists.

Because participants are known and vetted, permissioned chains typically favor faster, less energy-intensive consensus methods, such as Practical Byzantine Fault Tolerance or Raft, instead of open mining. This suits regulated use: banks, supply-chain consortia, and healthcare networks run frameworks like Hyperledger Fabric to share data across organizations while meeting KYC, AML, and audit requirements, often with private channels that keep sensitive data visible only to relevant parties.

The tradeoff is centralization risk: a small validator set can, in principle, collude or come under outside pressure, and unlike open networks there is no block-reward incentive, so the participating organizations must fund infrastructure, security, and governance themselves.