Public chains versus permissioned chains

A public chain, also called permissionless, accepts any participant who runs the software. Anyone can read the full history, send transactions and, depending on the design, help check new blocks. Bitcoin and Ethereum are the usual examples. Because strangers must agree without knowing each other, these networks lean on open rules, many independent nodes and economic penalties for cheating. The cost of that openness is that every rule change needs wide agreement, and the records are visible to anyone who looks. Addresses are pseudonymous rather than anonymous, so activity can often be traced by patient analysis once an address is linked to a named person or business.

A permissioned chain admits only approved participants. A company, a consortium of banks or a trade group decides who may run nodes, who may submit records and who may read them. Because the members are known and bound by contracts, such networks can use lighter agreement methods and keep data away from outsiders. The trade-off is trust: when a handful of organizations controls membership, the same handful can agree to alter rules or history, so the tamper-evidence a reader gets is only as strong as that group's integrity. Many networks sit between the two poles, for example with public data and a limited set of validators. Ask who may join, who may validate and who can change the software.