5 ms·

I think you're missing the point. For Bitcoin to continue to act as a decentralized currency ledger (with "settlement assurance"), then the network hash rate m

I think you're missing the point. For Bitcoin to continue to act as a decentralized currency ledger (with "settlement assurance"), then the network hash rate must remain high. Nobody is arguing that the code couldn't run on one processor, only that cryptocurrencies conceptually depend on this high hash rate

trixie_ 6y ago
It doesn't 'have' to be high. The hash rate could be 1/1000 of what it is today without any risk to 'settlement assurance'
- hn_acc_2 6y ago
  https://www.crypto51.app/coins/BTC.html https://www.crypto51.app/coins/BTC.html You could pay $384k to hire miners to 51% attack BTC right now (that is, if NiceHash had the capacity). If you cut the hash rate that much the cost would be only $400 or so. Does it sound like a secure trustless currency if anyone can pay $400 to gain 51% majority? EDIT: 51% attack != rewrite blockchain
  - trixie_ 6y ago
    There's a big difference between rewriting all history and rewriting a portion of it during an attack which costs 400k per hour. Also people may misinterpret 'rewriting history' as the ability to to change coins sent from A -> B to A -> C. Which it is not. Not saying an attack still isn't bad, but let's be clear what the extent of the damage could and could not be.
    - a1369209993 6y ago
      1: It's actually, under your proposal, "rewriting a portion of [history] during an attack which costs 400 [not 400 thousand] [dollars] per hour". 2: If you are A (and regardless of whether you're also C) and you sent money to B during the 400$/hr (less than a high-profile lawyer, and probably faster to boot) attack, then yes, changing coins sent from A -> B to A -> C is exactly what you can do.
      - Dylan16807 6y ago
        Though that's also assuming people don't do anything about the blatant attack.
        a1369209993 6y ago
        True, but if such a attack only costs 400$/hr there's going to quite a lot of them to do things about.
        qes 6y ago
        It's almost like if it were true that if it only cost $400/hr to 51% attack the BTC chain, we would actually see it happening much more often.
        a1369209993 6y ago
        Exactly, that's (very roughly) why it not only is, but must be, that you cannot, in fact, reduce the hash rate significantly without compromising the integrity of the ledger.
        Dylan16807 6y ago
        That depends on how you define integrity. If we cut the hash rate tenfold, which is definitely significant, you'd still need to find someone who has hundreds of thousands of dollars of motivation to perform an attack. Having that motivation is hard when it takes a huge amount of double spending all at once, the attack will damage the integrity of the coin, and clients can be modified to be highly resistant to it.
      - deleted 6y ago
        [deleted]
      - qes 6y ago
        > which costs 400 [not 400 thousand] [dollars] per hour No, it's $400,000 per hour. 0.009 BTC/PH/day to buy from NiceHash (https://www.nicehash.com/algorithm/sha256 https://www.nicehash.com/algorithm/sha256) 100,000 PH/day total hashrate of BTC network (https://www.blockchain.com/charts/hash-rate https://www.blockchain.com/charts/hash-rate) That's 450 BTC/day to buy 50% of the hash rate (as if you even could, that in itself is a ridiculous notion - NiceHash says they have only 300 PH). Or 18.75 BTC/hour. Or $185,000/hour. Of course, you're not going to buy 50% of the network's currently running hash power. You'd likely need closer to 100% of the network's current hash power to gain 51%. So, $400,000/hr. I mean really, does it pass any sort of common sense test that you could 51% the bitcoin network for $400 per hour?
  - jkhdigital 6y ago
    Correction: pay $400/hr to gain a temporary majority in the block mining lottery. You can do a variety of things with that majority power, but “rewriting history” is a bit misleading. Yes, you can probably get the network to discard some previously accepted blocks, but this only allows you to invalidate your own transactions plus the transactions that depend on them. Furthermore, any blocks that were mined under high hashpower still need the same hashpower to be re-mined. A one-time reduction in network hash power doesn’t make previously mined blocks easier to mine.
    - jayd16 6y ago
      Wouldn't you be able to buy goods, reverse the transaction, and buy more goods? That seems pretty significant if BTC is supposed to be ubiquitous (large transactions don't raise eyebrows) and cheap to use (meaning cheap to hash and cheap to takeover).
      - jkhdigital 6y ago
        Depends entirely on the policies of the merchant from which you’re buying goods. I have to admit, I had to read a couple dozen research papers about (theoretical) attacks on Bitcoin before I really understood the nuances. I’m expecting main chain transactions to be relatively expensive, but off-chain solutions can still be cheap. Yes, this requires some trust of a third party, but for small transactions that’s probably unavoidable. Not all transactions are created equal, and trustless settlement is expensive.
    - qes 6y ago
      Correction (where are you folks learning math? $400/hour, do you even have common sense?): 0.009 BTC/PH/day to buy from NiceHash (https://www.nicehash.com/algorithm/sha256 https://www.nicehash.com/algorithm/sha256) 100,000 PH/day total hashrate of BTC network (https://www.blockchain.com/charts/hash-rate https://www.blockchain.com/charts/hash-rate) That's 450 BTC/day to buy 50% of the hash rate (as if you even could, that in itself is a ridiculous notion - NiceHash says they have only 300 PH). Or 18.75 BTC/hour. Or $185,000/hour. Of course, you're not going to buy 50% of the network's currently running hash power. You'd likely need closer to 100% of the network's current hash power to gain 51%.
  - thebean11 6y ago
    Another caveat: pumping $384k/h into NiceHash would probably change the supply/demand dynamic drastically and increase the price.
    - hn_acc_2 6y ago
      Definitely. I don't really think this hypothetical attack would be possible, I only bring it up to demonstrate the effect that lowering the hash rate would have on the cost of disrupting the network.
    - Drakar1903 6y ago
      Let's not get hung up on details, if you have the resources to consider 51%ing Bitcoin for presumably nefarious purposes, you're probably a government/big finance/oligarch actor and you're probably not penny pinching.
- jkhdigital 6y ago
  Settlement assurance is roughly a function of (a) the expected cost of mining a block and (b) the total value of bitcoins moved in that block. In general, the larger the ratio of a to b, the less time a merchant must wait to reach a certain level of assurance.

trixie_ 6y ago

It doesn't 'have' to be high. The hash rate could be 1/1000 of what it is today without any risk to 'settlement assurance'

hn_acc_2 6y ago
https://www.crypto51.app/coins/BTC.html https://www.crypto51.app/coins/BTC.html You could pay $384k to hire miners to 51% attack BTC right now (that is, if NiceHash had the capacity). If you cut the hash rate that much the cost would be only $400 or so. Does it sound like a secure trustless currency if anyone can pay $400 to gain 51% majority? EDIT: 51% attack != rewrite blockchain
- trixie_ 6y ago
  There's a big difference between rewriting all history and rewriting a portion of it during an attack which costs 400k per hour. Also people may misinterpret 'rewriting history' as the ability to to change coins sent from A -> B to A -> C. Which it is not. Not saying an attack still isn't bad, but let's be clear what the extent of the damage could and could not be.
  - a1369209993 6y ago
    1: It's actually, under your proposal, "rewriting a portion of [history] during an attack which costs 400 [not 400 thousand] [dollars] per hour". 2: If you are A (and regardless of whether you're also C) and you sent money to B during the 400$/hr (less than a high-profile lawyer, and probably faster to boot) attack, then yes, changing coins sent from A -> B to A -> C is exactly what you can do.
    - Dylan16807 6y ago
      Though that's also assuming people don't do anything about the blatant attack.
      - a1369209993 6y ago
        True, but if such a attack only costs 400$/hr there's going to quite a lot of them to do things about.
        qes 6y ago
        It's almost like if it were true that if it only cost $400/hr to 51% attack the BTC chain, we would actually see it happening much more often.
        a1369209993 6y ago
        Exactly, that's (very roughly) why it not only is, but must be, that you cannot, in fact, reduce the hash rate significantly without compromising the integrity of the ledger.
        Dylan16807 6y ago
        That depends on how you define integrity. If we cut the hash rate tenfold, which is definitely significant, you'd still need to find someone who has hundreds of thousands of dollars of motivation to perform an attack. Having that motivation is hard when it takes a huge amount of double spending all at once, the attack will damage the integrity of the coin, and clients can be modified to be highly resistant to it.
    - deleted 6y ago
      [deleted]
    - qes 6y ago
      > which costs 400 [not 400 thousand] [dollars] per hour No, it's $400,000 per hour. 0.009 BTC/PH/day to buy from NiceHash (https://www.nicehash.com/algorithm/sha256 https://www.nicehash.com/algorithm/sha256) 100,000 PH/day total hashrate of BTC network (https://www.blockchain.com/charts/hash-rate https://www.blockchain.com/charts/hash-rate) That's 450 BTC/day to buy 50% of the hash rate (as if you even could, that in itself is a ridiculous notion - NiceHash says they have only 300 PH). Or 18.75 BTC/hour. Or $185,000/hour. Of course, you're not going to buy 50% of the network's currently running hash power. You'd likely need closer to 100% of the network's current hash power to gain 51%. So, $400,000/hr. I mean really, does it pass any sort of common sense test that you could 51% the bitcoin network for $400 per hour?
- jkhdigital 6y ago
  Correction: pay $400/hr to gain a temporary majority in the block mining lottery. You can do a variety of things with that majority power, but “rewriting history” is a bit misleading. Yes, you can probably get the network to discard some previously accepted blocks, but this only allows you to invalidate your own transactions plus the transactions that depend on them. Furthermore, any blocks that were mined under high hashpower still need the same hashpower to be re-mined. A one-time reduction in network hash power doesn’t make previously mined blocks easier to mine.
  - jayd16 6y ago
    Wouldn't you be able to buy goods, reverse the transaction, and buy more goods? That seems pretty significant if BTC is supposed to be ubiquitous (large transactions don't raise eyebrows) and cheap to use (meaning cheap to hash and cheap to takeover).
    - jkhdigital 6y ago
      Depends entirely on the policies of the merchant from which you’re buying goods. I have to admit, I had to read a couple dozen research papers about (theoretical) attacks on Bitcoin before I really understood the nuances. I’m expecting main chain transactions to be relatively expensive, but off-chain solutions can still be cheap. Yes, this requires some trust of a third party, but for small transactions that’s probably unavoidable. Not all transactions are created equal, and trustless settlement is expensive.
  - qes 6y ago
    Correction (where are you folks learning math? $400/hour, do you even have common sense?): 0.009 BTC/PH/day to buy from NiceHash (https://www.nicehash.com/algorithm/sha256 https://www.nicehash.com/algorithm/sha256) 100,000 PH/day total hashrate of BTC network (https://www.blockchain.com/charts/hash-rate https://www.blockchain.com/charts/hash-rate) That's 450 BTC/day to buy 50% of the hash rate (as if you even could, that in itself is a ridiculous notion - NiceHash says they have only 300 PH). Or 18.75 BTC/hour. Or $185,000/hour. Of course, you're not going to buy 50% of the network's currently running hash power. You'd likely need closer to 100% of the network's current hash power to gain 51%.
- thebean11 6y ago
  Another caveat: pumping $384k/h into NiceHash would probably change the supply/demand dynamic drastically and increase the price.
  - hn_acc_2 6y ago
    Definitely. I don't really think this hypothetical attack would be possible, I only bring it up to demonstrate the effect that lowering the hash rate would have on the cost of disrupting the network.
  - Drakar1903 6y ago
    Let's not get hung up on details, if you have the resources to consider 51%ing Bitcoin for presumably nefarious purposes, you're probably a government/big finance/oligarch actor and you're probably not penny pinching.
jkhdigital 6y ago
Settlement assurance is roughly a function of (a) the expected cost of mining a block and (b) the total value of bitcoins moved in that block. In general, the larger the ratio of a to b, the less time a merchant must wait to reach a certain level of assurance.