Bitcoin wallet collision

One of the greatest inventions in the history of computer security is Hashcash. Internet blights like spam and denial-of-service attacks are what economists call “tragedy of the commons” problems. They exploit the fact that it’s free to send email and make web requests. At zero cost, you can have a profitable business even at extremely low success rates.

One way to fix these problems is to impose tariffs that hurt bad actors without hurting good actors. For example, you could impose “postage fees” on every email and web request. Unfortunately, in practice, this is impossible, because you’d have to set up billing relationships between every computer that wants to communicate.

The brilliant idea behind Hashcash is to replace a monetary postage fee with a computational postage fee. In order to send an email, the sender first has to solve a math problem. Legitimate activities suffer an indiscernible delay, but illegitimate activities that require massive volume are hobbled.

Hashcash is a great idea, but cumbersome in practice. For example, the cost imposed on senders varies widely depending on the performance of their email servers. It also hinders legitimate bulk emails like clubs and retailers sending updates to their mailing lists.

The offline analogy to Hashcash is a postal system where senders are required to perform some work every time they want to send something. If you’re a lawyer, you need to practice some law before you send mail. If you’re a doctor, you need to cure something before you send mail. Etc. This of course would be a preposterous postal system.

Adam Smith called money “stored labor“. You do your work and then store your labor as money, which you can later exchange for labor stored by other people. Storing labor in the form of money turns out to be a very flexible system for trading labor, and far superior to the barter system of performing work whenever your counterparty performs work.