[Note: This is the second in a three part series. You can read the introductory post here and part three here.]
How Bitcoin Works (The Simplified Version)
In order to use the Bitcoin system, a user installs a “wallet” on their computer or mobile phone. Once installed the wallet generates a Bitcoin address (similar to an email address) that allows the user to send and receive payments. Bitcoins are divisible to 8 decimal places yielding a total of approx. 21×1014 currency units. This allows a person to spend a fraction of a Bitcoin (the current exchange rate as of April 15, 2012 is 1 Bitcoin = $95.36000). Unlike standard e-commerce and money transfer system, Bitcoin transactions are irreversible.
How Bitcoin Works (The More Complicated Version)
A Bitcoin is merely a chain of digital signatures attached to a transaction log. In the very first transaction of the system, Nakamoto’s computer program (which is open source and distributed across a peer-to-peer network) created 50 Bitcoins. When Nakamoto spent some of the coins, it created a new transaction that subtracted the amount from his account and credited it to the recipient’s. All such transfers entail the owner digitally signing a hash (a numerical value created by an algorithm) of the previous transaction and providing the public key for the encryption to the next owner. Both items are then added to the coin’s transaction log. A payee can verify the signatures to verify the chain of ownership, which prevents double spending of the same coins.
This transaction—and all subsequent exchanges—is distributed to the entire network for verification. Collections of transactions, known as “blocks,” are deemed valid when another computer on the network creates a transaction log for it that matches the previous blocks. To prevent the falsified logs from being accepted, the system must provide a means of verification that is prohibitively costly to any individual user, but relatively cheap for the network as a whole. As explained in The Economist:
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