10  Blockchain

A number of things can happen to the messenger and effectively to the

actual message. He could get captured, compromised, killed, and can be

replaced by another messenger by the city. This would lead to the armies

getting tampered-with information which may result in an uncoordinated

attack and prospective defeat. The Byzantine generals’ problem can be

solved using consensus mechanisms which can make sure their army can

actually carry out an attack as a unit.

Now let us apply the above Byzantine generals’ problem to the blockchain

as it has clear references to the blockchain as well. For instance, if you want

to send cryptocurrency like 1 Bitcoin to someone in a huge decentralised net-

work, how would you trust the other party and make sure someone has not

tampered with the transaction to change it from 1 to 10 Bitcoin? (Figure 1.5).

Blockchain consensus algorithms

• Proof of Work (PoW)

⚬

⚬PoW is used by the Bitcoin network. Miners solve cryptographic

puzzles to ‘mine’ a block for it to get added to the blockchain.

⚬

⚬This process requires a lot of computational power and energy.

⚬

⚬When a miner solves the puzzle, they present their block to the

network for verification.

⚬

⚬Once the block has been verified, it gets added to the blockchain.

⚬

⚬Miners get awarded a % of Bitcoin to solve the puzzle. One of

the disadvantages of PoW is that it takes an immense amount of

Coordinated Attack Leading to Victory

Uncoordinated Attack Leading to Defeat

Enemy City

Enemy City

Traitor

Traitor

Traitor

Figure 1.5  Byzantine general problem.