Zero Click is a dead easy payment protocol that will allow users to pay for resources online in the simplest way using Bitcoin. We came up with the idea when we noticed that the HTTP 402 payment required status code was unimplemented. We used Bitcoin because it allows us to transfer money with no registration and no lengthy approval for the person receiving the money.

The Bitcoin cryptocurrency records its transactions in a public log called the blockchain. Its security rests critically on the distributed protocol that maintains the blockchain, run by participants called miners. Conventional wisdom asserts that the protocol is incentive-compatible and secure against colluding minority groups, i.e., it incentivizes miners to follow the protocol as prescribed.

We show that the Bitcoin protocol is not incentive-compatible. We present an attack with which colluding miners obtain a revenue larger than their fair share. This attack can have signi cant consequences for Bitcoin: Rational miners will prefer to join the sel sh miners, and the colluding group will increase in size until it becomes a majority. At this point, the Bitcoin system ceases to be a decentralized currency.