Public, Private and Consortium Chains
The co-op's chain is a success, and three other co-ops in town want to use it for trading tools between them. Should anyone on the internet be able to join? Only approved co-ops? And is a blockchain even the right tool? Every blockchain project has to answer two questions before anything else: does this need a blockchain at all, and if so, who may take part.
The rule
First ask if you need a chain; then ask who may read, write and validate.
Networks differ in who holds three permissions:
| Type | Who can read | Who can send transactions | Who validates blocks | Typical use |
|---|---|---|---|---|
| Public (permissionless) | Anyone | Anyone | Anyone who meets the protocol's rules, such as doing work or locking stake | Open payment networks, public smart-contract platforms |
| Private | Whoever one organization allows | Whoever that organization allows | That organization's own nodes | Internal audit trails |
| Consortium | Usually members only | Members | A fixed group of member organizations | Settlement or trade records between firms |
Hybrid designs mix these. For example, a private chain can publish a fingerprint of its latest block on a public chain every hour, so outsiders can later check that its history was not rewritten.
A private chain run by one organization has a single controller, so it offers little over an ordinary database with an append-only audit log. A consortium makes more sense: its members want one shared record but do not want any single member to own it.
Where blockchains get used. Open payment networks and cross-border transfers; smart-contract platforms that run programmable agreements; supply-chain records where each company signs its own handover; registries of certificates or ownership that many parties need to check. Each case has several parties, one shared record, and no keeper that everyone trusts.
The shortcut
Before choosing a network type, run the "do we need a blockchain?" test. Pick a type only if it passes.
Several writers?
Four co-ops each record their own trades. Yes, more than one party writes.
If any of the first three answers had been no, such as a single writer or a party everyone already trusts, a shared database would be cheaper, faster and more private. Knowing when not to use a blockchain is part of understanding one.
Drills
Answer fast — trust the rule.
Who may validate blocks on a public, permissionless chain?
Five shipping firms want a shared record of container handovers that none of them owns and outsiders should not read. Which type fits best?
A retailer wants a tamper-evident log of its own stock changes, and it is the only writer. What is the best advice?
In the hybrid example, what makes the design hybrid?
Remember
- First ask if you need a chain; then ask who may read, write and validate.
- Shortcut: several writers, limited trust and no acceptable middleman means a blockchain may fit. Otherwise use a database.
- Trap: a private chain run by one organization still has one boss.