What:
The solution to the Consensus Problem in Blockchain. The protocol must satisfy:
- Termination: The protocol eventually finishes
- Agreement: All honest parties decide on the same output value.
- Validity: If all honest parties input the same value, then the output will be that value as well.
- What’s the use? Well because you could come up with a protocol that just outputs some arbitrary constant all of the time, but this rule prevents that. That way, the protocol will actually find agreement and utility.