Blockchain Developer's Guide

The nothing-at-stake attack

One of the issues in PoS systems is the threat of nothing-at-stake attacks. In a nothing-at-stake attack, a validator actually creates multiple blocks in order to spend tokens multiple times. Because of the low cost of creating blocks in PoS systems, there is no financial incentive to the network not to approve all the transactions, causing consensus to break down.

For instance, imagine a bad actor, Cain, who only has 100 tokens. He decides to try and cheat, and sends two messages to the network: one in which he sends his 100 tokens to Sanjay, and another where he sends his 100 tokens to Eliza. The network should accept either transaction, but not accept both. Typically, the nodes would have to come to consensus ...