This post is part of a series on how everyday investors can understand the word "consensus" in the context of blockchain networks.
Consensus is a general stance held by a group, or the act of coming to a unified stance on something. In the context of blockchain networks, consensus is the act of deciding what the canonical truth of the blockchain is. Put simply, which transactions actually get added to the ledger, and which do not, at any given time.
The Byzantine Generals Problem is a classic game theory and distributed systems problem written by L. Lamport, R. Shostak, and M. Pease. It outlines the challenges of coming to consensus without a central authority. This work is core to understanding how networks like Bitcoin and Solana can come to consensus with participants who have different incentives all over the world. Luckily, this problem is very easy to understand and can really illuminate the inner workings of blockchain networks.
The problem is best framed as having multiple generals that want to attack a city at the same time without any secure channel for communication.
Byzantium Is Under Siege, and We Are the Ones Attacking
So, there is an evil kingdom named Byzantium. To be clear, this is a fictional city, not the ancient Greek city that later became Constantinople. They have been an oppressive force to the seven kingdoms around them. The seven kingdoms have finally decided they need to do something about the Byzantine kingdom. However, the generals charged with coordinating the invasion have a big problem. They have no reliable method of communication. Byzantium, as part of its oppressive regime, has a network of spies all across the seven kingdoms, many of them likely in the upper ranks of the military. The generals, unfortunately, cannot meet in person to confirm a time and date. They must rely on intermediaries. How can the generals reliably figure out how to attack at the same time?
Becoming Tamper-Proof (Byzantine Fault Tolerant)
The generals came up with a great solution: recursive message passing. Essentially, each general would send a message to every other general with the proposed time and date of the attack. Then, each general would share all of the information they received along with the original date of attack they had shared. After multiple rounds of this, it would allow the generals to figure out which generals had compromised communication networks. At that point, the honest generals could go based on the majority vote for the date of attack. The generals created what is referred to as a Byzantine Fault Tolerant system, a system that can survive up to one third of its members being dishonest at any time.
How Is Bitcoin Byzantine Fault Tolerant?
Bitcoin solves the Byzantine Generals Problem using a consensus mechanism called Proof of Work. In the analogy of the generals, the blockchain ledger updates are the shared truth that everyone must agree on, and Proof of Work is the process that keeps it honest.
In Bitcoin's network, participants called miners compete to solve computationally expensive puzzles. The first miner to solve the puzzle earns the right to propose the next block of transactions to the network. Because this process requires real-world resources like electricity and hardware, attempting to deceive the network becomes extremely expensive. A dishonest miner would have to outspend the entire honest network to have any chance of success.
Once a block is proposed, every node in the network independently verifies that the transactions within it are valid and that the miner followed the rules. If someone tries to submit false information, the network rejects it. There is no need to trust any single participant because every node checks the work for itself.
This is what makes Bitcoin Byzantine Fault Tolerant. Even if some miners or nodes act dishonestly, as long as the majority of the network's computational power is controlled by honest participants, the system continues to function correctly. An attacker would need to control more than 50% of the network's total computing power to manipulate the blockchain. In practice, the cost of pulling this off on Bitcoin's network is astronomically high.
How Is Solana Byzantine Fault Tolerant?
Solana takes a different approach to achieving Byzantine Fault Tolerance. Instead of Proof of Work, Solana uses a Proof of Stake system combined with two key innovations: Proof of History and Tower Byzantine Fault Tolerance (Tower BFT).
One of the biggest challenges in any decentralized network is agreeing on when events happened. Without a central clock, nodes have to communicate back and forth just to establish the order of transactions, which slows things down considerably. Solana solves this with Proof of History, a cryptographic clock that timestamps every transaction directly on the blockchain. This gives the entire network a shared, verifiable timeline without requiring nodes to constantly check in with each other.
Tower BFT is Solana's custom implementation of Practical Byzantine Fault Tolerance. It builds on top of the timeline that Proof of History provides. Validators stake SOL tokens and vote on the validity of transactions. Each subsequent vote doubles the amount of time the network would need to stall before it could roll back that vote, making it increasingly difficult to reverse confirmed transactions as time goes on.
Because validators have real financial stake in the network, dishonest behavior is deterred through slashing, where a portion of a validator's staked tokens can be taken away as a penalty. As long as two thirds of the validators are acting honestly, the network remains secure and continues to process transactions. This combination of Proof of History and Tower BFT allows Solana to achieve high throughput and fast confirmation times while still maintaining Byzantine Fault Tolerance.
Conclusion
The Byzantine Generals Problem may have started as a thought experiment, but its implications are at the heart of how modern blockchain networks function. The core question it asks is simple: how do you get a group of people to agree on the truth when some of them might be lying? Bitcoin answered that question with Proof of Work, making dishonesty prohibitively expensive. Solana answered it with Proof of Stake combined with a cryptographic clock, making consensus fast and efficient while still resilient to bad actors.
Understanding this problem is key to understanding why blockchain technology works at all. Every time a transaction is confirmed on Bitcoin or Solana, these networks are solving the Byzantine Generals Problem in real time, ensuring that no single dishonest participant can corrupt the shared ledger. For everyday investors, the takeaway is straightforward. Consensus mechanisms are the reason you can trust a decentralized network with no central authority to keep an accurate record of who owns what.