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Let's say every single miner in the world added the same transaction to their block via trickery. The transaction was never initiated by the wallet holder. Would a block from these miners be added to the block chain?
If so what is the minimum number of miners needed to add a fake transaction to the block chain?
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Only the wallet holder can create a valid transaction. That's what makes them the wallet holder. The holder of a wallet is the person who can create valid transactions to claim the funds in that wallet.
So the transaction is not valid. Any block containing an invalid transaction is itself invalid. So everyone else (exchanges, wallets, etcetera) would ignore that block and any blocks mined on top of it. So all these miners would lose out on the money they could have made by mining valid blocks.
That's exactly what I mean tho. Let's say I have my own little network. I'm doing all the mining and I control all the wallets. Is it possible for me to transfer funds from wallet A to wallet B without using wallet A's private key given that I control every blockchain? – ivan – 2017-12-07T12:02:57.323
@ivan Only if everyone agrees to let you. Otherwise, whoever didn't agree to let you would not recognize that transaction as valid, leading to an immediate complete fork in the network between those who agree with you and those who disagree. You can't stay in the same network if you don't agree on the rules. A core rule on bitcoin is that transactions must be properly signed to be valid. – David Schwartz – 2017-12-07T12:04:16.973
Ok so if a majority agrees with my faulty transaction would that make the legitimate blocks the fork? – ivan – 2017-12-07T12:15:20.087
The network would immediately fork in two -- those who agree your transaction is valid and those who don't. Which side is "the fork" is a matter of opinion at that point. Interestingly, if the majority of hash power doesn't side with you, the fork will not happen. A majority of hashing power has to side with the disputed block or there's no fork. – David Schwartz – 2017-12-07T12:16:33.210
Thanks for explaining. What would such a fork look like through the eyes of an end user? Let's say there's a vending machine for candy that accepts bitcoin. A fork happens where the majority of the hashing power accepts a faulty transaction. The faulty transaction emptied a wallet which is now attempting to pay the vending machine. What would happen? – ivan – 2017-12-07T12:29:25.947
The vending machine would reject it because it ignores the invalid transaction, any block it's in, and any block built on top of it, so it would go with the minority side of the fork. The vending machine would not recognize the transaction paying it as valid either. (Unless the vending machine's owners chose to go with the fork along with the majority of hashing power, in which case it would accept it.) – David Schwartz – 2017-12-07T17:57:38.207
There is no power in the world that can force even a single user to accept a transaction or block that they believe is invalid. You do not need to go with the majority if you don't agree with them, but you lose the ability to interoperate with them. – David Schwartz – 2017-12-07T17:58:10.260
A transaction must be signed by a wallet holder. This is not mere "policy", it is a mathematical requirement. – abelenky – 2017-12-07T11:21:47.313