Goldman Sachs says blockchain technology “has the potential to redefine transactions” and will “change everything”. But anyone who claims to fully understand how blockchain works, and is not named Satoshi Nakamoto, is probably lying to you. And anyone who claims to be Nakamoto himself, is probably also lying to you. Fortunately, just like the internet, you don’t need to know how blockchain works to use it.
But here are the basics… a blockchain is a continuously growing list of records, called blocks, which are linked and secured using cryptography. By design, blockchains are inherently resistant to modification of the data, and serve as a public ledger of transactions between two parties. To date, the best analogy I’ve heard for blockchain compares it to a Google Doc:
“The traditional way of sharing documents with collaboration is to send a Microsoft Word document to another recipient, and ask them to save the document, make revisions to it, and send it back. The problem with this scenario was that you needed to wait to receive a return copy before you could see or make changes to the document. You are locked out of editing it until the other person is done with it. That’s how banks work today—they maintain money balances and transfer money by briefly locking access to the account (or decreasing the balance) while they make the transfer, then they update the other side, then re-open access (or update the balance).
With a Google Doc, all parties have access to the same document at the same time, and the most up-to-date version of that document is always visible and editable to all parties. This real-time shared Google Doc is just like a distributed blockchain ledger. The “real version” of the transaction is verified by analyzing all the available blocks on multiple computers and taking “the average”.
The decentralized and transparent nature is what makes blockchain highly secure and almost impossible to hack, because a hack to one ledger would cause a discrepancy in the entire network that will be ignored. Functionally, to hack the ledger one would have to hack all the computers on a network at the exact same time in order to change the “average”. For a currency like bitcoin, this would mean millions of computers. So the larger the network, the more stable the currency.