From the course: Building an Ethereum Blockchain App: 1 Introduction to Blockchain

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Arriving at consensus

Arriving at consensus - Ethereum Tutorial

From the course: Building an Ethereum Blockchain App: 1 Introduction to Blockchain

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Arriving at consensus

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- Blockchain is all about integrity and trust. So you don't have integrity if any node can just add a block at any time. So you have to agree, by you, I mean, all the nodes have to agree on what the valid blockchain is and which blocks are valid. So all the nodes have to agree on which new blocks can be added. They do that through a consensus mechanism. They come to consensus because blockchain is purely democratic. In other words, when anything over 50% of the nodes agree, that becomes the rule. So all you have to have is 50.000001 number of the nodes to agree that a block should be added and all the block, all the nodes have to agree to add that block. So the downside of that is that it's possible to attack a blockchain. If you can somehow take over and control just over 50% of the node, you can do what you want, but that's very, very difficult. Let's not worry about the attacks right now. Let's focus on…

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