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Practical byzantine fault tolerance in blockchain

Miguel Castro and Barbara Liskov developed a consensus technique called Practical Byzantine Fault Tolerance in the late 1990s. pBFT was engineered to function effectively in asynchronous systems, where there is no upper limit on the time it takes to get a response. It has little overhead time optimization. Its objective was to resolve several issues related to Byzantine Fault Tolerance solutions that were previously in existence. Blockchain and distributed computing are two examples of application fields.

What is BFT, or byzantine fault tolerance?

The ability of a distributed network to establish consensus (contract on the same value) even if some nodes in the network fail to reply or react with false information is known as Byzantine Fault Tolerance, or BFT. By using collaborative decision-making (including both proper and defective nodes), a BFT mechanism seeks to mitigate the impact of faulty nodes and protect against system breakdowns. The Byzantine Generals’ Problem is the source of BFT.

Byzantine Generals’ Problem

When nodes that are operating correctly come to an agreement on their values, byzantine fault tolerance is obtained. If the majority of nodes successfully answer, a default response can be issued, and a default vote value can be supplied to missing messages. Leslie Lamport proved that as long as 3m+1 processors are functioning correctly, if a minimum of m processors are defective, a consensus may be formed, meaning that higher than two-thirds of the processors must be truthful.

Different Types of Byzantine Failure

Two types of failures are taken into consideration. There are two types of node failure: arbitrary and fail-stop, where the node malfunctions and ceases to function. Below are a few examples of arbitrary node failures:

  • Inability to get back a result
  • Give a false response in return
  • React with a purposefully deceptive outcome
  • React to various system parts differently in terms of outcome

Benefits of PBFT:

1. Energy efficiency: pBFT does not require performing intricate mathematical calculations to reach widespread consensus (as in PoW). For every 100th block, Zilliqa uses pBFT in conjunction with PoW-like complicated calculations.

2. Transaction closure: Bitcoin’s Proof of Work process takes 10-60 minutes to validate each transaction, but once confirmed, no additional confirmation is required.

3. Low reward variation: Since every node in the network participates in responding to client requests, all nodes may be motivated, which results in low reward variance for decision-making nodes.

How does pBFT perform?

Byzantine state machine replication technology, or pBFT, is capable of operating with malicious nodes. It includes listing nodes in a sequential sequence, with one serving as the primary and the others as secondary. In the event of a failure, any qualified node can take over as the primary, switching from secondary to primary. The intention is for trustworthy nodes to use the majority rule to agree. A system that is Byzantine Fault Tolerant can operate with up to one-third of its nodes being malevolent.

pBFT consensus rounds have 4 phases

1. The principal (leader) node receives a request from the client.

2. All of the secondary (backup) nodes get the request broadcast from the primary (leader) node.

3. After completing the requested service, the primary and secondary nodes reply to the client.

4. The request is correctly fulfilled when the client receives “m+1” answers from various network nodes with the same results; so, m is the maximum number of defective nodes that can exist.

Challenges of pBFT

1. Sybil attacks: Due to scalability concerns, pBFT techniques can be used in connection with other mechanisms. However, executing Sybil assaults becomes more challenging as the number of network nodes increases.

2. Scaling:  The overhead of pBFT’s communication (with all the other nodes at every step) prevents it from scaling properly. An O(nk) time complexity arises from the response time to a request increasing proportionally with the number of nodes in the network.


Due to its potential to improve transaction speed and scalability while retaining high security, PBFT in blockchain technology has a wide range of real-world applications. For several businesses looking for dependable solutions, this makes it a viable alternative. Innovative breakthroughs in this subject are anticipated to increase as more options are discovered.