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If the nodes are what keep Bitcoin decentralized, what if some big internet company spun up 60%+ majority nodes?

What’s stopping them from manipulating the blockchain to change transactions?

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  • I have a complementary question to that : let's said i ask an exchnage platform to change bitcoin at address XXX , but I'm lying: address XXX has no bitcoins. But i set up "false nodes" in the Bictoin P2p network that said address XXX has bitcoins: how will the platform avoid to ask "my" nodes for the value of address XXX? And more largely, how would someone setting up a new node do the difference when downloading the blockchain between "good" and "false" nodes?
    – totalMongot
    Dec 30, 2021 at 19:52

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Every full node validates transactions and blocks. They do not change transactions based on some percentage.

Decentralization: What makes the bitcoin network decentralized? is it the nodes or the miners or both?

Nodes and consensus rules: https://bitcoin.stackexchange.com/a/108045/

Importance of economic nodes: https://en.bitcoin.it/wiki/Full_node#Economic_strength

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Block verifiers don't manipulate the block chain. What matters is the economical weight of those verifiers, not the number of node processes they run.

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Each Bitcoin transaction is signed using the private key(s) of the sender(s). The cryptographic signatures both provide authorization of the payments and ensure integrity of the transaction. The signatures commit to a digest of the transaction, which means that the signatures are invalid out of the context of exactly that transaction, even if the transaction were only changed by a single byte. Transaction without a signature or an invalid signature are not accepted of course.

The immutable valid transactions are then collected in blocks. The blocks are spaced out in time by means of a distributed lottery, the mining process. The mining process also ensures that a substantial amount of computation has been performed when a new block is found. Each block collects a group of transactions with a cryptographic commitment, rendering it just as immutable as the transaction data itself.

As these blocks propagate, each node individually verifies that all transactions and the block as a whole follow the the protocol rules. Someone spawning a multitude of nodes could potentially hamper propagation of block or transactions, isolate users on the network, or try discovering the original senders of transactions. Nodes alone cannot change either blocks or transactions, though.

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If the nodes are what keep Bitcoin decentralized, what if some big internet company spun up 60%+ majority nodes?

Nothing. There is nothing special about the number of nodes.

What’s stopping them from manipulating the blockchain to change transactions?

When one node talks to another node, it either sends valid messages or it sends invalid messages. If it sends invalid messages, the receiving node (if honest) will ignore it. If it sends valid messages, the receiving node (if honest) will honor it, but it will make that node do the right thing.

There is simply no way for any number of nodes to tell an honest node to do the wrong thing. A message either exists or it doesn't and it makes no difference how many places you receive the same message from. Nodes don't vote.

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