Blockchain and the two Generals' problem

Blockchain is fast becoming one of the best solutions in distributed ledger designs. Where a distributed ledger is a consensus of replicated, shared and synchronized digital data, blockchain employs a chain of blocks to successfully provide a secure distributed consensus.

Though blockchain is just one of the data types considered to be a distributed ledger, more than half of the world’s large corporations are looking into deploying blockchain, according to a study by an UK research firm.

While reading up on blockchain, the most interesting fact I came upon was about the Byzantine fault tolerance (BFT). The main advantage of blockchain was the fact that it had a high BFT.

BFT is the characteristics of a system that tolerates a class of failures known as the Byzantine General’s problem, which is considered the most difficult class of failures. The scary part of any failure that comes in the class of Byzantine is that they present different symptoms to different observers.

This term was coined from the – ‘Two Generals’ problem’

The story goes to describe the doings of a group of generals who were in charge of different sections of the Byzantine army. Now each section of the army is placed at separate locations, encircling the city they wanted to attack. These generals wish to come up with a plan to attack the city.

Since they are physically separated from each other and their army group, the generals must simply decide to either attack or retreat and send this message via their messengers. While some may prefer to attack and some retreat, the important point is to reach a consensus.

The problem is complicated with the presence of traitorous generals. If there are a group of 7 generals, 3 may pass the message to attack, the next 3 may favor retreat, while the 7th general might send a retreat message to one half of the team and an attack message to the other half. There is also the case of messages being misplaced by the messengers themselves.

The result would prove to be disastrous. Byzantine fault tolerance can be achieved if the loyal (non-faulty) generals have a unanimous agreement on their strategy.

The block chain is agreed upon by this consensus. By design, blockchains are resistant to data modification and once recorded, a given block cannot be altered without the alteration of all subsequent blocks. If a “bad” block is circulated, it may circulate for a while but will be eventually taken down by the majority consensus.

Each of the big four accounting forms in the world has been testing blockchain in various formats. While Ernst and Young has gone a step further by installing a bitcoin ATM in their Switzerland office, PwC, Deloitte and KPMG have taken a different path by testing private blockchains.

The research to understand more on blockchain continues and is surely a novel concept to wrap your brains around. The forefront on disruptive technologies for sure.