Byzantine Generals' Problem
This problem explores whether it is possible to reach an overall correct agreement in a situation where incorrect information may be transmitted either accidentally or intentionally using the transmission or individual objects in a group of objects that communicate with each other.
In general, in unreliable networks such as the Internet, it is an issue of how to create trust with strangers.
Blockchains build such trust using complicated calculations on each unique node. This is referred to as "Proof of work." Bitcoin's record and transactional security is maintained through proof of work.