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With bitcoin, it is agreed upon using byzantine consensus. The only way a bad actor can manipulate the ledger is if they own enough nodes to gain a majority, wh

With bitcoin, it is agreed upon using byzantine consensus. The only way a bad actor can manipulate the ledger is if they own enough nodes to gain a majority, which is virtually impossible. After just a handful of bit times is economically and mathematically impossible to reverse the contract. I suggest listening to this Tim Ferris podcast with Nick Szabo: http://tim.blog/2017/06/04/nick-szabo/ http://tim.blog/2017/06/04/nick-szabo/ The entire idea is that no arbiter is truly neutral, no third party is truly trustworthy. Block chain is the onset of FAT protocols and trustful computing. If the poor of the world can understand the social mobility that crypto currency affords them, there will be no stopping it, in my opinion.

scient 9y ago
> The only way a bad actor can manipulate the ledger is if they own enough nodes to gain a majority, which is virtually impossible. Im not buying that. If there is a way, someone will do it. This actually seems like a huge vulnerability to me. Especially when we are talking about specialized blockchains where the participation isnt every internet connected person in the world. How do you prevent that from happening?
linkregister 9y ago
> The only way a bad actor can manipulate the ledger is if they own enough nodes to gain a majority, which is virtually impossible. At times the leading BTC mining pool has controlled greater than 50% of the nodes. Would this not be enough to alter the ledger?
- danblick 9y ago
  Yes, you could abuse that power to allow double-spending. For what it's worth, I'd say I'm a bit concerned about this, but it seems many aren't. https://news.ycombinator.com/item?id=14485430 https://news.ycombinator.com/item?id=14485430
- Taek 9y ago
  Notably, 'altering the ledger' here has a very restricted meaning. You can spend money, then reverse the spend back into your wallet. Or you can commit to a piece of information, then delete it. But you can't alter the core protocol or fundamental network rules. If you do, the other nodes will ignore you.
  - kahnpro 9y ago
    But this is the fundamental question it's all about... the expectation that the other nodes will ignore you. Somehow "the other nodes" have reached consensus about what protocols or rules to follow, and this is where we end up back at human governance.
jakewins 9y ago
> If the poor of the world can understand the social mobility that crypto currency affords them Can you expand on how crypto currencies relate to positive social mobility? Off-handedly it seems to me it would be the opposite, although I'm admittedly fuzzy on this.. In theory crypto currencies reduce rent-seeking from intermediaries; since much financial rent seeking is established as percentages of an exchange (like a credit card transfer), removing those rents will give bigger net advantages to those transferring large amounts than those transferring small ones. Not saying removing rent seeking is bad (it's awesome!), but I don't see how that does anything but increase the difficulty for someone with low capital to catch up; rather it should be doing the opposite.
- patrickk 9y ago
  > Can you expand on how crypto currencies relate to positive social mobility? Bringing those who are unbanked into the global financial system is a powerful way to help lift people out of poverty. In many cases, banks are unwilling or unable to serve the poor, so cryptocurrencies could potentially fill the gap. I don't think any current cryptocurrencies will achieve this, but there is some research being done on "stablecoins" which could fit the bill.
  - russdpale 9y ago
    Cryptocurrency is already doing this, I don't have the names offhand, butt, (Ill eave the typo, hehe) there are several regions in Africa where bitcoin is a primary currency being traded.
    - acdha 9y ago
      Do you have any sources for that claim? Given the massive existing mobile payment deployment it seems like a very ambitious target.
    - knopkop 9y ago
      > I don't have the names offhand Tether?
sciyoshi 9y ago
OP's argument is that this distributed consensus algorithm works only if there is already consensus about which algorithm to use in the first place! If you and I disagree about which block history is valid (for example, because my history includes blocks with a lower difficulty), then the assumptions are no longer valid and there's a hard fork. Also, note that a 51% attack can only exclude transactions or allow double spending - the ledger still can't be arbitrarily manipulated since transactions are signed by private keys.
danblick 9y ago
Is "byzantine consensus" an appropriate term? I think it's typically used when there's agreement on the list of nodes participating in the network. (The nodes can agree to change the list of participants, Lamport wrote about it in "Reconfiguring a State Machine".)* With "blockchain" / proof of work, computing power substitutes for voting power: you pass state transitions by controlling a majority of the compute power rather than a majority of the voting power. Have you seen "byzantine consensus" used in the second context (with proof of work) also? (*) When I think of the Byzantine consensus problem, it's when: - not every node has to vote in each round (so that the system can make progress even if some nodes fail); - you can authenticate (e.g. with cryptography) that messages come from the appropriate sender (but not whether that sender is acting "honestly"); - the goal is to reach consensus, i.e., if any node concludes that some proposition (i.e. state transition) has passed, no nodes will ever agree on contradictory proposition.

scient 9y ago

> The only way a bad actor can manipulate the ledger is if they own enough nodes to gain a majority, which is virtually impossible. Im not buying that. If there is a way, someone will do it. This actually seems like a huge vulnerability to me. Especially when we are talking about specialized blockchains where the participation isnt every internet connected person in the world. How do you prevent that from happening?

linkregister 9y ago

> The only way a bad actor can manipulate the ledger is if they own enough nodes to gain a majority, which is virtually impossible. At times the leading BTC mining pool has controlled greater than 50% of the nodes. Would this not be enough to alter the ledger?

danblick 9y ago
Yes, you could abuse that power to allow double-spending. For what it's worth, I'd say I'm a bit concerned about this, but it seems many aren't. https://news.ycombinator.com/item?id=14485430 https://news.ycombinator.com/item?id=14485430
Taek 9y ago
Notably, 'altering the ledger' here has a very restricted meaning. You can spend money, then reverse the spend back into your wallet. Or you can commit to a piece of information, then delete it. But you can't alter the core protocol or fundamental network rules. If you do, the other nodes will ignore you.
- kahnpro 9y ago
  But this is the fundamental question it's all about... the expectation that the other nodes will ignore you. Somehow "the other nodes" have reached consensus about what protocols or rules to follow, and this is where we end up back at human governance.

jakewins 9y ago

> If the poor of the world can understand the social mobility that crypto currency affords them Can you expand on how crypto currencies relate to positive social mobility? Off-handedly it seems to me it would be the opposite, although I'm admittedly fuzzy on this.. In theory crypto currencies reduce rent-seeking from intermediaries; since much financial rent seeking is established as percentages of an exchange (like a credit card transfer), removing those rents will give bigger net advantages to those transferring large amounts than those transferring small ones. Not saying removing rent seeking is bad (it's awesome!), but I don't see how that does anything but increase the difficulty for someone with low capital to catch up; rather it should be doing the opposite.

patrickk 9y ago
> Can you expand on how crypto currencies relate to positive social mobility? Bringing those who are unbanked into the global financial system is a powerful way to help lift people out of poverty. In many cases, banks are unwilling or unable to serve the poor, so cryptocurrencies could potentially fill the gap. I don't think any current cryptocurrencies will achieve this, but there is some research being done on "stablecoins" which could fit the bill.
- russdpale 9y ago
  Cryptocurrency is already doing this, I don't have the names offhand, butt, (Ill eave the typo, hehe) there are several regions in Africa where bitcoin is a primary currency being traded.
  - acdha 9y ago
    Do you have any sources for that claim? Given the massive existing mobile payment deployment it seems like a very ambitious target.
  - knopkop 9y ago
    > I don't have the names offhand Tether?

sciyoshi 9y ago

OP's argument is that this distributed consensus algorithm works only if there is already consensus about which algorithm to use in the first place! If you and I disagree about which block history is valid (for example, because my history includes blocks with a lower difficulty), then the assumptions are no longer valid and there's a hard fork. Also, note that a 51% attack can only exclude transactions or allow double spending - the ledger still can't be arbitrarily manipulated since transactions are signed by private keys.

danblick 9y ago

Is "byzantine consensus" an appropriate term? I think it's typically used when there's agreement on the list of nodes participating in the network. (The nodes can agree to change the list of participants, Lamport wrote about it in "Reconfiguring a State Machine".)* With "blockchain" / proof of work, computing power substitutes for voting power: you pass state transitions by controlling a majority of the compute power rather than a majority of the voting power. Have you seen "byzantine consensus" used in the second context (with proof of work) also? (*) When I think of the Byzantine consensus problem, it's when: - not every node has to vote in each round (so that the system can make progress even if some nodes fail); - you can authenticate (e.g. with cryptography) that messages come from the appropriate sender (but not whether that sender is acting "honestly"); - the goal is to reach consensus, i.e., if any node concludes that some proposition (i.e. state transition) has passed, no nodes will ever agree on contradictory proposition.