What does “permissionless” mean?
At the heart of the much-hyped “blockchain” technology lies not a blockchain, surprisingly, but a consensus mechanism. A consensus mechanism does what it says; it helps everyone on the network agree, or reach consensus, on a shared computation and records of that computation. In the Bitcoin network, for example, the shared computation is the continual creation of a list of digital currency transactions made between users. In Ethereum it’s the state changes of a globally-accessible virtual machine. A fundamental question in the design of any consensus mechanism is who can participate and how do they participate in order to reach consensus over some shared computation. For many years it was assumed that useful consensus mechanisms could only be developed if the participant computers were identified through channels outside of the decentralized computing system itself. In other words, it had been assumed that useful consensus mechanisms could only be designed as closed or permissioned