What Is Byzantine Fault Tolerance, and How Does It Ensure Blockchain Stability?
Trust and security are vital to blockchain technology—and the Byzantine fault tolerance (BFT) consensus mechanism is at the core of a blockchain’s safety.
BFT ensures that blockchains continue operating, even if some network participants are unreliable or malicious. So what is BFT, how does it work, and why is it so crucial for blockchain technology?
What Is Byzantine Fault Tolerance?
Byzantine fault tolerance refers to the ability of a network or system to continue functioning even when some components are faulty or have failed.
With a BFT system, blockchain networks keep functioning or implementing planned actions as long as most network participants are reliable and genuine. This means that over half or two-thirds of the nodes on the blockchain network must agree to validate a transaction and add it to the block.
For compromised nodes to cause malice on a Byzantine fault-tolerant blockchain, they must be in the majority. This malice can be in the form of double spending, a51% attack, aSybil attack, and so on.
Byzantine fault tolerance in blockchain technology originates from the Byzantine general problem pioneered by Leslie Lamport, Marshall Pease, and Robert Shostak. This concept became prominent when they published a paper, with a copyhosted by Microsoft, called ‘The Byzantine Generals Problem (PDF)’ in 1982.
Lamport, Pease, and Shostak described the case of a group of generals from the Byzantine army camping outside an enemy city. Each general had their own army and needed to communicate and make a unanimous decision on whether to attack or retreat.
The problem was carrying out a joint action amid some compromised generals. This dilemma was called a Byzantine fault, and when a system successfully tackles this problem, it is said to be Byzantine fault-tolerant.
The Byzantine fault-tolerant concept was then applied to the cryptocurrency blockchain network. In the crypto space, the generals are the nodes that validate crypto transactions.
How Does the Byzantine Fault Tolerance Work?
Decentralized networks implement Byzantine fault tolerance via consensus rules or protocols. All the nodes in the network must adhere to these protocols or algorithms if they want to participate in validating and processing transactions.
For a transaction to be validated, processed, and added to a growing block, most nodes must agree that the transaction is authentic through the network’s consensus algorithm. Bitcoin, Ethereum, and other proof of work (PoW) and proof of stake (PoS) blockchains employ BFT algorithms.
In the PoW consensus algorithm, the miners on the network solve cryptographic puzzles to validate and produce blocks recording transactions. The miner that solves the puzzles first wins the right to add the transaction to the growing block and earn the block reward. But the miner must publish proof that they solved the puzzle to add the block.
The mining process in PoW blockchains requires expensive computers or mining rigs. This high cost disincentivizes miners from sharing false information because other participants would reject it. It also reduces the likelihood of malicious actors gaining control of most nodes in the system.
Meanwhile, with the PoS consensus mechanism, you muststake a certain amount of crypto tokensto earn the right to validate the transaction. Then, if the network protocol selects you, you can add the transaction to the growing block and earn the block reward.
PoS systems solve Byzantine faults using different methods. For instance, Ethereum uses the Casper algorithm, which requires at least two-thirds of the nodes to reach a consensus on blocks. Ultimately, PoS systems need most nodes to agree on blocks before they can be added.
These blockchains use BFT consensus algorithms to resist the nodes in the minority that do not agree with the consensus. This way, the blockchain network can proceed with its function, rejecting faulty or dishonest transactions.
The Role of Byzantine Fault Tolerance in Blockchain Technology
Blockchain technology relies on Byzantine fault tolerance for these reasons:
Limitations of Byzantine Fault Tolerance
Byzantine fault tolerance has brought about tremendous benefits to the blockchain industry. However, the system still has issues, especially the practical Byzantine fault-tolerant consensus algorithm (pBFT).
The practical Byzantine fault tolerance is an optimized form of the original Byzantine fault tolerance. pBFT works through an asynchronous system consisting of a primary leader node and other backup nodes. In this system, the malicious nodes cannot be more than the honest nodes, usually not up to one-third. The nodes always communicate with each other to ensure that most nodes (the honest ones) agree on the state of the network.
Some limitations of the pBFT include the following:
Six Popular BFT Blockchain-Based Platforms
Here are some blockchains that integrate the Byzantine fault tolerance mechanisms.
1. Bitcoin
Bitcoin incorporates Byzantine fault tolerance into its network through the proof of work consensus protocol. The blockchain’s PoW consensus algorithm mandates all the nodes on the blockchain to check the data structure, block size, block timestamp, block header hash, and the first transaction on every data.This process, called data hashing, uses computational power.
2. Ethereum
Previously using PoW,the Ethereum blockchain has transitioned to a PoS systemthat solves its Byzantine problems. Network validators stake their Ether tokens, and the protocol selects honest validators to process transactions, validate blocks, and vote for a head of a chain. The protocol forces stakers to be honest, making attacking the network prohibitively expensive.
EOSIO blockchain achieves a consensus via an asynchronous byzantine fault tolerant (aBFT) layer and a delegated proof of stake (DPoS) layer. The aBFT layer confirms each block of transactions until it is the last irreversible block (LIB). The DPoS layer then confirms the LIB as the final, irreversible block.
Ripple does not use either of the PoW or PoS consensus mechanisms. Instead, it uses the XRP Ledger Consensus Protocol, a Byzantine fault-tolerant consensus mechanism. The blockchain continues to function normally if the untrusted validators are less than 20% of the total validators. This system prevents double-spending and improves blockchain integrity.
Kadena uses a ScalableBFT consensus mechanism to confirm blocks. The blockchain combines Bitcoin’s PoW system with altering decentralized multiple parallel blockchain consensus mechanisms that are energy efficient, scalable, and secure and provides a much-improved output than Bitcoin’s system. This setup, called “Chainweb,” allows Kadena to carry out up to 480,000 transactions per second (TPS) with 20 chains running concurrently.
The consensus mechanism for the Quorum cryptosystem is the Istanbul Byzantine fault tolerance (IBFT) consensus mechanism. QuorumChain delegates the rights to vote to a pool of nodes (validators); one node is made the proposer to initiate the block confirmation while the other nodes validate the block. If more than 1/3 of the nodes in the pool behave incorrectly, the block will not be inserted.
The Future of Byzantine Fault Tolerance Is Bright
As long as cryptocurrencies and blockchain technology continue to exist, Byzantine fault tolerance and other consensus mechanisms shall, too. However, these mechanisms will likely continue to evolve.
Initially, Ethereum integrated BFT using PoW, but Ethereum switched from PoW to PoS and updated its BFT algorithm. Likewise, you’ll continue to see newer and better systems with time. Remember, the crypto space is constantly evolving.
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