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> I don't think it's at all far-fetched to suggest that if Mastercard or Andreessen Horowitz is in a position to decide how much of other people's money they're

> I don't think it's at all far-fetched to suggest that if Mastercard or Andreessen Horowitz is in a position to decide how much of other people's money they're entitled to, they might decide that the answer is "all of it". Paypal and Google do this on a regular basis. Here in Argentina, the banking system decided that the answer was "75% of it" in 2001, with respect to dollars; in the US, the Federal Government did precisely the same thing in 1933 with gold. The consensus model of blockchain would at least require Mastercard, Andreessen Horowitz and other validator nodes to be in agreement about stealing / being entitled to the money, which seems less likely. That said, this is one of the flaws of having only a few nodes validating transactions. Libra went this route instead of Bitcoin's proof of work consensus model. With Bitcoin's proof of work consensus, 51% of the miners in the world would have to collude in order to steal funds. All of the comments I see that say blockchain has no use case, seem to miss another point you raise, in that Bitcoin can not be seized, even by government (like the US government did with Gold), unless they had miner control and the public didn't continue to operate and spin up new miner nodes. This seems unlikely considering that the miners could lose their funds, if they did not prevent a counterparty having 51% control of the network. This is a protection that Bitcoin has, that Libra does not. The government could go to corporations in the Libra association and tell them to do what they want. In terms of other use cases, I think having an immutable ledger, that can't be changed by one party, or even a few parties with DB access, also seems like a compelling use case for blockchain / cryptocurrency. Libra isn't really a cryptocurrency by this standard though, although Bitcoin is. Also, just to put it out there, Mastercard, PayPal, Stripe, Visa and a few others already have left the Libra association.

kragen 7y ago
> The consensus model of blockchain would at least require Mastercard, Andreessen Horowitz and other validator nodes to be in agreement about stealing / being entitled to the money, which seems less likely. Right, I think you, I, and Libra's developers are in agreement about this being a significant risk and one that using a blockchain effectively mitigates, in precisely the way you say, but Diehl and Green aren't.
phlip9 7y ago
+ FWIW, 51% of the mining power only allows you to double-spend, not arbitrarily modify the existing ledger. + Since Libra uses a HotStuff variant, you need to control 2/3+ of the voting power to violate safety, i.e., double-spend. In exchange, however, you only need to control 1/3+ to halt progress (liveness).
- kragen 7y ago
  If you can halt progress, you can make any particular person's holdings impossible to spend (if you can identify them), by refusing to include any blocks that include transactions from them. That isn't quite as lucrative as simply confiscating someone's holdings, but it's close; you can demand a ransom of a sufficient fraction of their holdings, perhaps 5% to 50%, depending on human nature.
  - phlip9 7y ago
    I wouldn't say it is quite the same threat model, but certainly a powerful attack vector if you happen to control 1/3+ of the voting power. In the unlikely event that someone does compromise 1/3+ of the voting power, the remaining validators can always hard fork to a new quorum, though this is an expensive and highly synchronized affair.

kragen 7y ago

> The consensus model of blockchain would at least require Mastercard, Andreessen Horowitz and other validator nodes to be in agreement about stealing / being entitled to the money, which seems less likely. Right, I think you, I, and Libra's developers are in agreement about this being a significant risk and one that using a blockchain effectively mitigates, in precisely the way you say, but Diehl and Green aren't.

phlip9 7y ago

+ FWIW, 51% of the mining power only allows you to double-spend, not arbitrarily modify the existing ledger. + Since Libra uses a HotStuff variant, you need to control 2/3+ of the voting power to violate safety, i.e., double-spend. In exchange, however, you only need to control 1/3+ to halt progress (liveness).

kragen 7y ago
If you can halt progress, you can make any particular person's holdings impossible to spend (if you can identify them), by refusing to include any blocks that include transactions from them. That isn't quite as lucrative as simply confiscating someone's holdings, but it's close; you can demand a ransom of a sufficient fraction of their holdings, perhaps 5% to 50%, depending on human nature.
- phlip9 7y ago
  I wouldn't say it is quite the same threat model, but certainly a powerful attack vector if you happen to control 1/3+ of the voting power. In the unlikely event that someone does compromise 1/3+ of the voting power, the remaining validators can always hard fork to a new quorum, though this is an expensive and highly synchronized affair.