Byzantine Fault Tolerance Simplified, A Brief Overview On Its Types

Byzantine fault Tolerance is a critical aspect of distributed systems that ensures they can handle faults including, the malicious nodes now before we dive into BFT, let’s talk about distributed systems.

What is a Distributed System

A distributed system is a collection of independent computers that work together to achieve a common goal. In contrast to a single computer, a distributed system can handle more significant workloads and provide redundancy and fault tolerance however, distributed systems pose unique challenges, including how to ensure that all nodes agree on the same result this is where Byzantine Fault Tolerance comes in.

Byzantine General’s Problem

The classic Byzantine General’s problem is a thought experiment that illustrates the challenges of achieving consensus in a distributed system the problem is as follows

Imagine a group of Byzantine generals who are planning to attack a city the generals are located in different parts of the city and must communicate with each other to agree on a strategy however, some of the generals may be traitors who want to sabotage the plan that is resilient to the traitors, the problem is how can the loyal generals agree on a plan that is resilient to the traitors attempts to disrupt the process?

In essence, the byzantine general's problem demonstrates the challenges of achieving consensus in a distributed system, especially when some nodes are malicious or faulty. So that’s the problem now what about the solution?

Practical Byzantine Fault Tolerance

Well, one solution to the Byzantine general's problem is a practical Byzantine fault tolerance or PBFT. In a nutshell, PBFT is an algorithm that ensures a group of computers can agree on something even if some of them are trying to cheat or disrupt the process wondering how it works. Well, PBFT works by using a replicated state machine approach where each node has a copy of the same state machine and runs the same set of instructions. When a new value needs to be agreed upon a node proposes a value and other nodes replicate the state machine by running the same instructions on their copy, however before the decision is made, a multi-step voting process takes place to ensure the majority of nodes agree on the value. In the first step, the proposer sends a message to all nodes receiving the proposal and replying with a message indicating whether they agree or not. Once the proposer receives a sufficient number of votes the value is accepted and the state machine is updated with the new value the process is repeated for each new value that needs to be agreed upon pbft ensures that a decision is made only when a  majority of the nodes agree on it and that this decision is final and cannot be changed, if a node behaves maliciously the other nodes can detect this and exclude the dishonest node from the consensus process

A drawback of Practical Byzantine Fault Tolerance

Although pbft is a promising solution, it also has a drawback. PBFT requires a relatively large number of nodes to operate efficiently also, pbft assumes that nodes are not only byzantine fault-tolerant but also self-verifying which means they can detect if they have been hacked and report it to the other nodes, and if you think practically this can be difficult to achieve in a real-world scenario

Federated Byzantine Agreement (FBA)

Another solution to the Byzantine General's problem is the Federated Byzantine Agreement (FBA). FBA is a consensus algorithm that is used in blockchain technology and it’s designed to be more efficient than pbft. In pbft nodes are grouped into federations and each federation has its consensus algorithm. In FBA Nodes vote for other nodes in the federation to become validators, and once a sufficient number of votes has been cast, the validator is added to the federation, the validator then participates in the consensus process and agrees on the new value.

PBFT vs FBA, which is more efficient

If we compare the two, then one can say easily that FBA is more efficient than pbft because it allows for more flexible participation in the consensus process, nodes can join or leave a federation at any time, and there can be many federations running in parallel and inherently one of the main benefits of fba is that it’s scalable, which means it can handle a large number of nodes without sacrificing over performance that’s also the reason why fba is used in several blockchain projects, including the stellar network which is known for its fast and low-cost transactions

Drawback of Federated Byzantine Agreement

FBA also has its limitations one is that it’s not as fault-tolerant as pbft because it relies on the assumption that most nodes are honest and here, if a federation is controlled by malicious nodes they can manipulate the consensus process and undermine the security of the network

Conclusion

To summarize byzantine fault tolerance is a key concept in ensuring the reliability and security of distributed systems pbft and fba are are two possible solutions to the byzantine generals problem with their own advantages and drawbacks  pbft is more fault-tolerant but requires a larger number of nodes while fba is more efficient but relies on trust between federations pbft is an algorithm that ensures consensus is reached only when a majority of nodes agree and it assumes that nodes are byzantine fault-tolerant and self-verifying, fba on the other hand is a consensus algorithm that groups nodes into federations and allow for more flexible participation in the consensus process it’s scalable but less fault-tolerant than pbft both pbft and fba have their pros and cons, and their suitability depends on the specific requirements of the distributed system however  we should equally account for the fact that they are critical tools for ensuring the security and reliability of distributed systems in a world where malicious actors are increasingly common