What Is Byzantine Fault Tolerance?

3 Dec 2023 by Harry Newman 5 min read

What is Byzantine Fault Tolerance? Byzantine Fault Tolerance is a computer system’s ability to continue operating and reaching consensus even if some nodes fail or act maliciously.

A reliable computer system must be able to function even if one or more of its components fail.

What Is Byzantine Fault Tolerance

The term originates from the Byzantine Generals Problem.

Best explained with military tactics in a scenario where different Byzantine generals gather around an enemy city before attacking it.

Picture several generals of the Byzantine army who are besieging a city, each commanding a portion of the army, the generals need to decide unanimously whether to attack or retreat.

If all generals attack at the same time, they will win, but if they attack at different times, they will most likely lose.

Not all generals are loyal, there can be miscommunication between the generals, causing false messages to be sent.

The challenge lies in making a unified decision even if some generals might not be loyal. There needs to be a safe means to agree on a plan and carry it out.

These types of problems are known as Byzantine Faults.

Essentially, the Byzantine Generals Problem describes the difficulty parties have in arriving at a consensus without relying on a trusted central authority.

This is a difficult problem to solve.

Byzantine Fault Tolerance In Blockchain Technology

From a computing perspective, ensuring that a system remains functional even if some components fail is paramount.

This is evident in scenarios like aviation, where aeroplanes are designed to operate safely even when not all systems are functioning optimally.

The challenge of the Byzantine Generals' Problem is unique to decentralised systems, as these systems lack a central, reliable source to verify information. In contrast, centralised financial systems, such as banks, rely on the inherent trust that they will act honestly and not defraud their customers.

In these systems, an authority like a government is trusted to intervene if this trust is breached. However, centralisation does not solve the Byzantine problem; rather, it bypasses it by sacrificing trustlessness for efficiency, opting not to address the problem directly. Despite this, centralised systems are still susceptible to corruption by the central authority.

In blockchain technology, particularly in peer-to-peer networks, nodes can be likened to the generals in the Byzantine Generals' Problem.

Ensuring that the network operates consistently, even with potentially unreliable nodes, is critical.

Byzantine Fault Tolerance (BFT) addresses this challenge by enabling nodes to function correctly and reach unanimous decisions.

There are numerous reasons why a distributed computer system might fail, including software defects, malicious attacks, or hardware malfunctions.

Byzantine faults are almost inevitable in every computer system. Blockchain technology, with its reliance on a distributed ledger, employs a robust consensus mechanism to combat this. BFT serves a crucial role in ensuring all participating nodes in a blockchain agree on the ledger's state, thus creating trust and reliability in the system.

BFT operates by implementing a consensus mechanism where nodes in a network agree on a specific decision or value.

The process of reaching a consensus includes several steps:

Proposal: A node proposes a specific value or decision.
Voting: Other nodes vote on the proposed value or decision. The voting process is designed to accommodate the possibility of false information from some nodes.
Agreement: Once a consensus is reached among the nodes, the decision is finalised.

This mechanism ensures that a majority consensus is achieved, even in the presence of faulty or malicious nodes.

By doing so, BFT maintains the integrity and functionality of the system, underpinning the trust and reliability critical to blockchain networks.

Bitcoin and the Byzantine Fault Problem

Bitcoin represents the first successful solution to the Byzantine Generals' Problem, a milestone achievement in the field of digital currency.

It accomplishes this through blockchain technology, a public, distributed ledger that chronicles the entire history of all Bitcoin transactions.

The crux of solving the Byzantine Generals' Problem in Bitcoin's context lies in achieving consensus among all nodes in the network about the sequence and occurrence of transactions.

This consensus allows for verifying Bitcoin ownership and establishing a functional, trustless monetary system without relying on a centralised authority.

This feat is achieved using Bitcoin's consensus mechanism known as Proof-of-Work (PoW). PoW sets a clear and objective framework of rules for the blockchain's operation.

To send information or blocks, to the blockchain, a network participant – typically referred to as a miner – must provide proof of their contribution to the creation of that block.

This proof involves expending significant amounts of energy to run mining software, a process that inherently incentivizes the publication of honest information due to the substantial work and resources required.

Once transactions are recorded on the blockchain, altering or tampering with them becomes exceptionally challenging.

Each node in the network independently verifies the validity of each block based on the PoW.

If any node attempts to disseminate false information, other nodes in the network will promptly detect this, flag it as invalid, and disregard the fraudulent data.

Since every node is capable of independently verifying information on the Bitcoin network, there is no need to place trust in other network participants, rendering Bitcoin a trustless system.

In addition to PoW, other consensus mechanisms, such as Proof-of-Stake (PoS), have been developed to address the Byzantine Generals' Problem.

These alternative mechanisms also aim to ensure network consensus and security, albeit often with different operational requirements and efficiencies compared to PoW.

Each consensus model plays a vital role in maintaining the integrity and trustlessness of their respective blockchain networks, crucial for the decentralised nature of cryptocurrencies.

Final Thoughts

Byzantine Fault Tolerance is essential to blockchains, its ability to ensure consensus and maintain system integrity, even in the presence of malicious or faulty nodes makes it an invaluable asset to digital infrastructure.

As we reach more mass adoption the importance of having a decentralised system will be crucial to allowing a more secure, reliable and trustworthy foundation for all users.