Byzantine General

By | 23rd July 2017

Blockchain provides a solution to the Byzantine General’s Problem. In this problem, several army factions surround a castle they hope to sack. A general leads each faction and one general is the lead general.

Only a simultaneous attack ensures victory. Also, since the factions surround the castle, they are dispersed, making centralized command difficult.

The generals must send messages between the factions to relay the attack time.

However, some generals are traitors and will not obey the command and worse, will relay the wrong attack time to the other generals. The generals do not know who is loyal and who is a traitor and there is no way to find out.

So, how do the factions ensure a coordinated attack to sack the castle?

Let’s apply this scenario to the blockchain. In a distributed ledger, any inputs (the messages) to the ledger (the agreed upon time of attack) must be trusted. Digital networks usually have millions of members (the generals) who are dispersed globally and there is no centralized command (no central governance), and it is impossible for you to know all the members.

So how can you trust the other members of the network and ensure that the inputs to the distributed ledger are accurate and moreover, ensure that the ledger itself has the correct information?

Blockchain solves this problem and in the case of our Byzantine general, ensures that he can send trusted messages and lead a successful coordinated attack.

So the blockchain solves the issue of ensuring the message is:

  • Delivered in a timely manner
  • The original manner can be read by anyone in the knowledge it was written by the General
  • The original manner can be read by anyone in the knowledge it has not been tampered with

How the Byzantine General Sacked the Castle: A Look Into Blockchain by Debraj Ghosh

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