# Simply read Byzantine fault tolerance

Translator's Note: This article simplifies the various mathematical models that may appear in the "Byzantine General" problem. It is pointed out that the core of the Byzantine problem settlement is that "although there are destroyers, the chain with the most computational power can be regarded as the main chain because The cost and competition of being a traitor (publishing a false block) is so difficult that it is almost impossible.” Due to the decentralization and autonomous nature of the blockchain, how to reach consensus among many participating nodes while allowing certain errors And to pass the information, this is a core issue, and Nakamoto has done it first.

When you start to understand the blockchain, you often hear a term: Byzantine Fault Tolerance (BFT). If you want to figure it out, a term that sounds very strange and mysterious, we can explain it with a story.

In 1982, a mathematical problem called General Byzantine was raised. The mathematical principles behind it are not described in detail here. In essence, the Byzantine General question is a story about a war between two empires.

Knight Spirit: Medieval War

An empire was placed in a solid wall, and the other empire's digital generals surrounded the city, and each general led the army to wait for the attack. The two empires are evenly matched.

If all the generals agree and attack at the same time, they will have enough power to defeat the empire in the wall and win the war.

However, for whatever reason, if they can't coordinate and launch an attack at the same time, even if only one general misses the information, their siege plan will fail and lose the war.

The Byzantine General question explores a key area of ​​cryptography. In fact, this is the core of cryptography, the essence of which is how to exchange information in an environment where some people may "rebel."

Now, the only way for these generals to communicate is to send a disguised messenger to pass through the city to pass information to other generals. There will always be a risk here. If you are one of the generals, you will get a message from one of the messengers, then how do you know, or how can you be more confident than random decisions that the information you get is reliable and has not been tampered with?

This was also a hypothesis proposed in 1982 and was not resolved until 2008. That year's anonymous Satoshi Nakamoto proposed a solution that made Bitcoin possible.

In essence, the solution is to have all the generals have as many mathematicians as possible.

“When we talk about Byzantine fault tolerance, we are talking about the generals having more authority, more mathematicians, or more computing power than the empire within the city walls.

So, if I can hire more mathematicians, that means I can encrypt the information I pass through the city more and more complexly; but if the power balance of the generals outside the city becomes very favorable, and they can The encryption method used is so complicated that any mathematician in the city really has no chance or a very small chance to intercept the message, then decrypt and change it, fast enough for the generals to barely notice. Content and re-encrypt.

This is Byzantine fault tolerance.

This is what we have seen so far, and the fault-tolerant mechanisms used in most public blockchain solutions include Bitcoin and Ethereum, which I mentioned earlier, although Ethereum is transitioning to the Proof of Stake.

So when it comes to blockchain, when you hear Byzantine fault tolerance, what it means is that if the power and hashing power on the blockchain is stronger than the chain, it becomes safe.

Bitcoin is currently the largest blockchain network with more than 30,000 nodes. Ethereum has more than 16,000 nodes, which provides us with a high degree of security and immutability. The power on these networks is so powerful that there really isn't much chance that an opponent can control as much power as possible to attack the data on that blockchain.

If someone wants to do this, the economic opportunity behind it is likely to be that they will spend more money to use all the computing power at the same time, which may be unbearable.

You will hear a lot about 51% of attacks on this issue. Finally, we can say that Byzantine fault tolerance is the root of cryptography. It simply studies how we can safely pass information back and forth when there are “enemy opponents and malicious actors”. It is all security that exists in the blockchain. And the basis of immutability.

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The author, Demiro Massessi, is translated by the "Blue Fox Notes" community Dyna.