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If China is able to do it, wouldn't Bitcoin lose all its value ?

DINKDINK 9y ago
No. Miners can only double spend transactions if they have > 50 % of the hash rate. The only purpose of miners is to add proof of work to in exchange for new coins that users value. If the proof of work is on a chain that contains valid transactions and conforms to consensus rules, it'll be valuable.
- namelost 9y ago
  Bitcoin is not the only game in town, there would be a mad scramble to Ethereum et al.
  - DINKDINK 9y ago
    I prefer a blockchain that is immutable, has controlled inflation. Bitcoin users can always choose a different PoW algorithm if a threat actor coerces too high of a percentage of SHA256 mining equipment
- tboyd47 9y ago
  But that would just create an invalid side chain and result in all the miners' hash power being wasted. https://bitcoin.stackexchange.com/questions/55316/what-happens-if-a-miner-publishes-a-block-which-contains-an-invalid-transaction https://bitcoin.stackexchange.com/questions/55316/what-happe...
  - freeloop2 9y ago
    Your link doesn't address the question. It's about an invalid transaction within the block, not the refusal to place a particular transaction into one. With over 50% of mining power you can definitely do this.
    - tboyd47 9y ago
      https://en.bitcoin.it/wiki/Invalid_block https://en.bitcoin.it/wiki/Invalid_block > Clients will ignore invalid blocks when determining which chain is difficultywise-longest. Mining clients will not build on top of invalid blocks. Clients will not propagate invalid blocks (or invalid transactions). Proof of work does not mean full nodes trust miners blindly. It only means they prefer the longest chain that follows the rules. Like I said, yes, with 50% mining power you can double-spend all you want. But other nodes know what you are doing, expel you from the network, and discard your work, just as if you had 25% of hash power or 0.1%. The Bitcoin blockchain is not a democratic system where the majority always wins.
      - freeloop2 9y ago
        A double spend isn't an invalid block. This renders the rest of your argument invalid.
        tboyd47 9y ago
        > For each input, if the referenced output has already been spent by a transaction in the main branch, reject. https://en.bitcoin.it/wiki/Protocol_rules https://en.bitcoin.it/wiki/Protocol_rules
        freeloop2 9y ago
        That isn't a double spend!
- XR0CSWV3h3kZWg 9y ago
  If you control >50% of the hash power you can also censor tx by ignoring any block that contains them.
  - coryfklein 9y ago
    Same story if you control 1% of hash power. Anyone can ignore any block, but you can't completely block a transaction unless you prevent it from being included in ANY block. Even if 90% of the hash power is blocking your transactions it just means it takes 10x longer for your transaction to go through.
    - Dylan16807 9y ago
      This is not ignoring transactions, this is ignoring any block that contains those transactions. You make your own pure chain that's longer, and everyone else uses it too because it's longer. If someone else mines a block then such a transaction can temporarily get a confirmation or two, but the 90% steamroller will come by and quickly reduce it back to 0 confirmations on the longest chain. If someone with 1% hash power ignores certain blocks, they make a chain that's totally irrelevant in their own corner. If someone with 60% hash power does it, they win.
TearsInTheRain 9y ago
China can exert a lot of control on it's business regarding bitcoin but they wouldnt be able to control or censor the network so this wouldnt kill bitcoin.

No. Miners can only double spend transactions if they have > 50 % of the hash rate. The only purpose of miners is to add proof of work to in exchange for new coins that users value. If the proof of work is on a chain that contains valid transactions and conforms to consensus rules, it'll be valuable.

namelost 9y ago
Bitcoin is not the only game in town, there would be a mad scramble to Ethereum et al.
- DINKDINK 9y ago
  I prefer a blockchain that is immutable, has controlled inflation. Bitcoin users can always choose a different PoW algorithm if a threat actor coerces too high of a percentage of SHA256 mining equipment
tboyd47 9y ago
But that would just create an invalid side chain and result in all the miners' hash power being wasted. https://bitcoin.stackexchange.com/questions/55316/what-happens-if-a-miner-publishes-a-block-which-contains-an-invalid-transaction https://bitcoin.stackexchange.com/questions/55316/what-happe...
- freeloop2 9y ago
  Your link doesn't address the question. It's about an invalid transaction within the block, not the refusal to place a particular transaction into one. With over 50% of mining power you can definitely do this.
  - tboyd47 9y ago
    https://en.bitcoin.it/wiki/Invalid_block https://en.bitcoin.it/wiki/Invalid_block > Clients will ignore invalid blocks when determining which chain is difficultywise-longest. Mining clients will not build on top of invalid blocks. Clients will not propagate invalid blocks (or invalid transactions). Proof of work does not mean full nodes trust miners blindly. It only means they prefer the longest chain that follows the rules. Like I said, yes, with 50% mining power you can double-spend all you want. But other nodes know what you are doing, expel you from the network, and discard your work, just as if you had 25% of hash power or 0.1%. The Bitcoin blockchain is not a democratic system where the majority always wins.
    - freeloop2 9y ago
      A double spend isn't an invalid block. This renders the rest of your argument invalid.
      - tboyd47 9y ago
        > For each input, if the referenced output has already been spent by a transaction in the main branch, reject. https://en.bitcoin.it/wiki/Protocol_rules https://en.bitcoin.it/wiki/Protocol_rules
        freeloop2 9y ago
        That isn't a double spend!
XR0CSWV3h3kZWg 9y ago
If you control >50% of the hash power you can also censor tx by ignoring any block that contains them.
- coryfklein 9y ago
  Same story if you control 1% of hash power. Anyone can ignore any block, but you can't completely block a transaction unless you prevent it from being included in ANY block. Even if 90% of the hash power is blocking your transactions it just means it takes 10x longer for your transaction to go through.
  - Dylan16807 9y ago
    This is not ignoring transactions, this is ignoring any block that contains those transactions. You make your own pure chain that's longer, and everyone else uses it too because it's longer. If someone else mines a block then such a transaction can temporarily get a confirmation or two, but the 90% steamroller will come by and quickly reduce it back to 0 confirmations on the longest chain. If someone with 1% hash power ignores certain blocks, they make a chain that's totally irrelevant in their own corner. If someone with 60% hash power does it, they win.

TearsInTheRain 9y ago

China can exert a lot of control on it's business regarding bitcoin but they wouldnt be able to control or censor the network so this wouldnt kill bitcoin.