A public blockchain is a blockchain that is available to the public. It is also referred to as a permissionless blockchain, because it does not require permission to participate. This is why some view public blockchains as a more democratic way of doing things. Most cryptocurrencies use public blockchains.

The public part of a public blockchain is the address and the transactions moving into and out of the address. An example of an ETH address is:

0x0125e2478d69eXaMpLe81766fef5c120d30fb53f

You can also think of the address as an “account.” This is helpful perspective to understand blockchain as a system of accounting. A ledger is a record of accounts. A public blockchain is a distributed ledger for keeping track of cryptocurrency accounts.

A cryptocurrency wallet is an application connected to an address that is used to manage that address. The owner of the address can send and receive value from the address using the wallet.

The fundamental feature of public blockchains is that the address is viewable by anyone. This is the “public key.” It is an aspect of blockchain that applies to Bitcoin, which you can see on the Bitcoin blockchain. The blockchain is public by design so that there is a single record of what it is in every address.

Knowing an address on a public blockchain does not allow access to the address. Access is provided by combining the public key with a “private key.” The private key is a unique code that is only available to the owner of the address. Using the private key allows the owner of the address to move cryptocurrency into and out of the address. As mentioned, a wallet is an application used for this purpose.

Because addresses and the history of all prior transactions is public knowledge, it is possible to verify whether a transaction is legitimate based on the record of transactions associated with an address. This is the role of mining.

Cryptocurrency uses encryption to maintain security and privacy.

Public blockchains are also public in the sense that they run on open-source code. This makes them totally transparent in their operation.