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Ultimate Byzantine Fault Tolerance(BFT) Guide 2026

Practical Byzantine Fault Tolerance is an algorithm for consensus that was introduced in the mid 90s and early 2000s by Barbara Liskov and Miguel Castro. It was created to operate effectively within asynchronous(no upper bound as to when the reply to the request is expected) systems.

It has been optimized to work with low cost of operation. The goal of the software was to address numerous issues that are associated with accessible Byzantine Fault Tolerance Solutions. Applications comprise distributed computing as well as blockchain.

What is Byzantine Fault Tolerance?

Byzantine Fault Tolerance(BFT) refers to an attribute of distributed system that helps attain consensus(agreement to the same values) even if one or more of the nodes in the network are unable to react or provide incorrect data.

The purpose of the BFT method is to guard against failures in the system using collaborative decisions making(both correctly and incorrect nodes) that aims to limit the impact of the defective nodes. Byzantine Fault Tolerance BFT comes in Byzantine Generals Problem.

Byzantine Generals Problem

The solution was clearly explained in paper written by LESLIE LAMPORT ROBERT SHOSTAK and MARSHALL PEASE of Microsoft Research in 1982:

Imagine that many divisions of the Byzantine army camp out in city that is in the enemys territory and each is led by its general. Generals are able to talk to one another through messengers. When they have observed the enemy then they have to decide on an agreed upon plan of attack. There are some generals might be traitors seeking to stop the generals who are loyal to them from coming to an agreement. Generals need to choose what time to begin attacking the city. However they must have majority of their forces in order to do so simultaneously. Generals need an algorithm that will ensure that (a) every general loyal to them agree on the same strategy of attack and (b) only few of traitors cant cause generals who are loyal to them to follow an unsound strategy. All loyal generals follow the rules of the algorithm they must however the traitors can do whatever they like. The algorithm has to guarantee the conditions (a) regardless whether the traitors are guilty or not. Generals who are loyal must not be content to reach an the same conclusion but they should also be able to agree on fair solution.

Byzantine fault tolerance could be realized if properly working nodes within the network achieve an agreement regarding their value. It is possible to assign default vote value assigned for messages that are not received i.e. We can suppose that the message sent coming from particular point is “faulty” when the message has not been delivered within predetermined period of time.

In addition we may give default answer when the majority of nodes are responding with the correct number. Leslie Lamport proved that if you have 3m+1 functioning processors and it is possible to reach consensus(agreement for the similar state) is possible when at least one processor is defective meaning that in total over two thirds of entire number of processors must be truthful.

Types of Byzantine Failures:

There are two kinds of failures to be considered. One of them is fail stop(in which the device ceases to function and fails) as well as arbitrary node failure. The most common arbitrary failures can be found below:

Inability to report the result
Correct the result with an error
You can respond with an intentionally misleading outcome
Different results will be given to various parts of the system.

Benefits of PBFTT:

Efficiency in energy The pBFT algorithm can create distributed consensus while not requiring intricate math computations(like PoW). PoW). Zilliqa uses pBFT with PoW like complicated computations. every 100th block.
Finality of the transaction It is important to note that transactions don’t require multiple confirmations(like for PoW system in Bitcoin in which every node separately examines all transactions prior to including the new block on the blockchain. The confirmation process could take anywhere from 10 to 60 minutes depending on how many individuals confirm the latest block) once they are approved and finalized.
Variance in reward is low Each node within the network participates in responding to demand of the client and therefore every node could be incentive based which results in very low reward variance for nodes involved in the decision making process.

How does pBFT work ?

pBFT Byzantine Fault Tolerance attempts to offer an efficient Byzantine state machine replication system that is able to function even when nodes that are malicious are running the system. Nodes within pBFT Byzantine Fault Tolerance enabled distributed system are arranged in sequential order and one of them is one of the primary(or that is the node leading) as well as others being called secondary(or those that backup).

It is important to note that any node within the system could change to become the primary one by moving into secondary status and then primary(typically during the event in the event of primary failure). The aim is to have every honest node contributes to coming to common understanding of the status of the system by applying the rule of majority.

practically Byzantine Fault Tolerant System can operate under the conditions that the total amount of malicious nodes should not be more than the equivalent of one third of the total nodes within the system. When the nodes grows it becomes more secured. The consensus rounds of pBFT are divided into four phases(refer to the picture below):

The client makes an inquiry via node primary(leader) the node.
The primary(leader) node transmits its request to every secondary(backup) Nodes.
The nodes(primary and secondary) provide the services requested in return. They then send with response to the user.
It is successful after the client has receivedm+1 responses from various nodes within the network that produce similar results. it is the highest number of nodes with faulty connections allowed.
The primary(leader) node changes each view(pBFT consensual rounds) and is replaced by the secondary node.
View change protocol
If certain amount of time has passed without the node in charge broadcasting an invitation to backups(secondary). If required there is majority honest nodes may decide on the validity of the leading node and substitute it for the following leading node that is in line.
The limitations of pBFT
The consensus model pBFT Byzantine Fault Tolerance works well only if the number of nodes within the distributed network is low due to the huge cost of communication that grows exponentially for each additional node that joins the network.
Sybil attacks Mechanisms for pBFT are vulnerable to Sybil attacks that occur when an entity(party) has control over multiple identities. With the increase in numbers of nodes within the network grows the risk of sybil attacks becomes more difficult to execute. Since pBFT has scaling issues it is also possible that they are often utilized in conjunction with another mechanism(s).
- Scaling The pBFT algorithm does not grow well due to its communication(with every other node throughout the entire process) cost. The more nodes within the network increase(increases in the form of O(n^k) (where the messages are n and the number k represents how many nodes) also increases the amount of time required to respond to the requests.
Platforms that use the pBFT version:
Zilliqa pBFT in conjunction with PoW consensus
- Hyperledger Fabric permissioned version of the pBFT
- Tendermint pBFT + DPoS(Delegated Proof of Stake)
Different forms of pBFT:
To improve the performance and quality of pBFT in specific scenarios and situations numerous variants were suggested and implemented. few of them include :
RBFT Redundant BFT
- ABsTRACTs
- Q/U
- HQ Hybrid Quorum Protocol for Byzantine Fault Tolerance BFT
- Adapt
- Zyzzyva Speculative Byzantine Fault Tolerance
- Aardvark

What is Byzantine Generals Problem?

In the year 1982 The Byzantine Generals Problem was created through Leslie Lamport Robert Shostak and Marshall Pease. Byzantine Generals Problem can be described as an impossible result that means that the answer for this issue hasn’t been identified yet in addition to helping us to appreciate the value of blockchain technology. Its essentially game theory problem which provides an explanation of the degree of decentralized players issues in coming to consensus with no central authority.

The Byzantine army is broken into numerous battalions within this well known problem known as the Byzantine Generals Problem each division being led by general.
Generals communicate through messenger to reach common strategy of attack in which each battalion coordinates and attacks on all sides to succeed.
The likelihood is that the criminals may attempt to undermine their plans by intercepting or altering the message.
In the end that the goal of this competition is to encourage every faithful commander to come to an agreement in the absence of imposters altering their strategies.

Money and Byzantine Generals Problem

Money is commodity which has value that is the same across the entire society. That means everyone must agree on the worth of particular amount of money in spite of any differences. In the beginning rare metals and rare items were selected as currency because their worth was recognized across the entire society.

However certain situations such as rare metals the purity of the material cannot be determined in absolute certainty. Moreover determining the quality was difficult task which proved to be inadequate for daily trade and it was decided replacing gold by central entity with high degree of trust selected by people of the community to create and preserve the financial system. However it became apparent that these central authorities no matter how they were still weren’t completely secure because it was easy for them to alter the information.

Centralized systems don’t solve the Byzantine Fault Tolerance Generals issue and requires that data be confirmed in clear manner but central systems do not provide transparent information thereby increasing the chance of corrupted data.
They avoid transparency to be efficient and avoid having to deal completely with the problem.
The primary issue with centralized systems is the fact that they are susceptible to being manipulated by central authorities meaning that data is susceptible to manipulation by any with control over the database since centralization puts the entire power of single central the decision maker.

Therefore Bitcoin was invented to make the system of money decentralized using blockchain to make money verifiable counterfeit resistant trustless and separate from central agency.

How Bitcoin Solves the Byzantine Generals Problem?

in the Byzantine Fault Tolerance Generals Problem In the Byzantine Generals Problem the non alternative agreement that all faithful generals must agree to is blockchain. Blockchain is free ledger distributed and centralized that stores the details of every transaction.

If the users in Bitcoin Bitcoin network or nodes were able to agree regarding the transactions they took place and the order in which they took place it would be possible to verify authenticity of the owner and build and secure system of money without the requirement for central authority.

Because of its decentralization it relies heavily on consensus method for confirming transactions. Blockchain is peer to peer system which offers its users confidence and security. The distributed ledger that it uses makes it different from other networks. Blockchain technology can be incorporated to any system that needs an appropriate confirmation.

Proof Of Work: The network would have to be provable counterfeit resistant and trust free in order to solve the Byzantine Generals Problem. Bitcoin was able to overcome the Byzantine Generals Challenge by utilizing an approach called Proof of Work to make an objective clear regulation for blockchain. Proof of Work (PoW) is the process to add new blocks of transactions into the cryptocurrencys blockchain. The job is to create the hash (a lengthy sequence of numbers) which matches the hash of the block currently in use.

Counterfeit Resistant Proof of Work is requirement for network participants to provide proof of their efforts with valid hash to have their block i.e. bit of data that is considered to be legitimate. Proof of Work demands miners to invest large amounts of energy as well as cash to create blocks. It also encourages miners to provide accurate data as well as safeguarding the network. Proof of Work is among the few ways to allow the decentralized network to be able to agree on one source of truth. This is vital for any monetary system. There is no chance of conflict or manipulation of data on the blockchain as the rules are independent. The guidelines that define what transactions are legal and those that and the process of selecting those who are able to mint new bitcoin are two goals.
Valid: Once block is transferred to the blockchain its extremely difficult to remove making the history of Bitcoin unchangeable. Therefore the users of the blockchain are able to always come to an agreement on the status of the network and the transactions within it. Every node independently checks that the blocks meet the Proof of Work criteria and whether transactions fulfill the additional criteria.
Secure: If any network member is attempting to spread false details the entire network will instantly recognize it as in error and disregard the information. Since each node of the Bitcoin network is able to verify all data on the network there’s no reason to trust the other members of the network and this makes Bitcoin an untrustworthy system.

Byzantine Fault Tolerance (BFT)

It is believed that the Byzantine Fault Tolerance has been created for inspiration to solve the Byzantine Generals problem. The Byzantine Generals Problem which is rational thought experiment in which several generals are required to attack the city was where the concept for Byzantine Fault Tolerance BFT came from.

Byzantine Fault Tolerance is one essential characteristics in the development of reliable blockchain rules or features. It is also known as tolerance.
When two thirds or more of the systems members can achieve consensus while the system continues to function correctly it is referred to that it has Byzantine Fault Tolerance BFT.
The most well known blockchain networks consensus protocols like proof of work proof of stake and proof of authority. Each of these protocols has Byzantine Fault Tolerance BFT features.
For the creation of an open network BFT is essential. Byzantine Fault Tolerance BFT is vital.

The consensus technique establishes the specific network structure. In this case Byzantine Fault Tolerance BFT has leader and peers that have the ability to and do not validate. To maintain the flow of Blockchain SC transactions and the uniformity of the global state by local replay of transactions the consensus messages have to be passed between the appropriate peer. Newer and more innovative approaches to creating Byzantine Fault Tolerance BFT system will be developed and tested as more people and businesses explore distributed and decentralized systems. The systems that utilize Byzantine Fault Tolerance BFT are used also for other areas that are not blockchain related including energy from nuclear sources as well as space exploration and air travel.

Byzantine Fault Tolerance Generals Problem in Distributed System

In order to resolve the issue trustworthy nodes (such as computers and other physical devices) should be able to reach an agreement in the presence of disreputable nodes.

When it comes to the Byzantine Fault Tolerance accordance problem an unspecified processor sets specific value which has to be agreed on and all non faulty processors must be in agreement on this value. Each processor is assigned their own initial value within the agreement issue. Moreover every processor that is not defective must reach consensus on common value. The Byzantine Fault Tolerance Army’s location is evident through computers networks.

Divisions can be thought of as computers that are nodes within the network and the commanders are programs that run an account that tracks activities and other events in the order they happen byzantine fault tolerance. Ledgers are identical across all systems and should one be modified all the ledgers also get updated in the event that the changes prove to be valid and therefore the distributed ledgers must have common understanding.