5 ms·

(I work for Algorand) This is false. The BFT protocol that Algorand uses guarantees that each round may have exactly one block (up to our security assumptions w

(I work for Algorand) This is false. The BFT protocol that Algorand uses guarantees that each round may have exactly one block (up to our security assumptions with regard to honest stake); this is one of the protocol’s “safety” guarantees. In the case that a large number of participating nodes crash, the network will refuse to produce a block until a sufficient amount of stake begins participating again. Nodes that fall behind can use the standard catchup protocol — the one that nodes new to the network make use of — to pick up where they left off.

thesausageking 8y ago
Calling the case of the network halting "safety" doesn't help things. To walk through a plausible example: let's say 3 Chinese services control 35% of the stake of Algorand. Without warning or any public announcement, the Chinese government steps in and forces them to turn off their servers. The Algorand network will now stop functioning as it can't reach 2/3rds. Hours go by and no one is able to transact. At this point, the network needs to decide how to proceed. Does everyone just agree to take a complete loss? Most likely, a group of other stakers would work on a proposal to deal with it, maybe by removing the offline tokens. How do they get consensus for this proposal? And, if they do it, what do they do if the Chinese stakers come back online?
- justicz 8y ago
  In this case the Chinese government can kill the liveness of the network (preventing it from producing new blocks), but not the safety of the network (they can't fork the chain). Your question has changed into: "doesn't the system break when a malicious party controls 35% of the stake?" To which the answer is yes. If a malicious party can control 35% of the stake, that is very bad. I should add, though, that if you know your machine is going to be taken down, you can mark your account as "offline" via a special transaction, which will allow the network to proceed without you by increasing the probability that others will be chosen to be on a committee.
  - thesausageking 8y ago
    "If a malicious party can control 35% of the stake, that is very bad." That didn't happen in this case. The Chinese government never took anyone's keys or controlled any stake, which is the point of the example. The malicious parties don't need control. They don't need to take anyone's keys or access their servers. They just need to be able to bring it offline, which is much easier to do. Which raises the question I asked and you didn't answer: if 35% of the stake goes offline with no signs of coming back, how do participants reach consensus?
    - justicz 8y ago
      You are right to call out the difference between "control" in the sense of keys and "control" in the sense of a network adversary. I should have been more careful with my wording there. It is true that if 35% of the participating stake is suddenly prevented from contacting the network, no new blocks will be created. The word "participating" is important -- you can have stake that is not participating in the agreement protocol, but that is still spendable. The only way I can think of to mitigate the scenario you've described would be this: before going offline, you can broadcast a transaction which essentially removes your stake from the pool of participating coins until you're able to come online again. This would ensure the network can proceed without you.
- Vervious 8y ago
  TBH I'd rather my assets be frozen, in the case of the network halting, than allow double spending, just because some honest players lost internet.
- throwaway415415 8y ago
  Yes people can duck with a network by cutting cables. This works with all internet protocols.
  - thesausageking 8y ago
    If 99% of Bitcoin's hashrate gets taken off the internet, it keeps going without any problem. That's the beauty of a decentralized cryptocurrency. There's no central node and it's supremely fault tolerant. Algorand has a lot of interesting technology and may have some use cases. But it's more like a distributed database / voting system than a true cryptocurrency.
    - throwaway415415 8y ago
      That is not true. If network partitions happen in bitcoin you are utterly ducked. The system will fork and good luck to recover from that with all the double spendings.

thesausageking 8y ago

Calling the case of the network halting "safety" doesn't help things. To walk through a plausible example: let's say 3 Chinese services control 35% of the stake of Algorand. Without warning or any public announcement, the Chinese government steps in and forces them to turn off their servers. The Algorand network will now stop functioning as it can't reach 2/3rds. Hours go by and no one is able to transact. At this point, the network needs to decide how to proceed. Does everyone just agree to take a complete loss? Most likely, a group of other stakers would work on a proposal to deal with it, maybe by removing the offline tokens. How do they get consensus for this proposal? And, if they do it, what do they do if the Chinese stakers come back online?

justicz 8y ago
In this case the Chinese government can kill the liveness of the network (preventing it from producing new blocks), but not the safety of the network (they can't fork the chain). Your question has changed into: "doesn't the system break when a malicious party controls 35% of the stake?" To which the answer is yes. If a malicious party can control 35% of the stake, that is very bad. I should add, though, that if you know your machine is going to be taken down, you can mark your account as "offline" via a special transaction, which will allow the network to proceed without you by increasing the probability that others will be chosen to be on a committee.
- thesausageking 8y ago
  "If a malicious party can control 35% of the stake, that is very bad." That didn't happen in this case. The Chinese government never took anyone's keys or controlled any stake, which is the point of the example. The malicious parties don't need control. They don't need to take anyone's keys or access their servers. They just need to be able to bring it offline, which is much easier to do. Which raises the question I asked and you didn't answer: if 35% of the stake goes offline with no signs of coming back, how do participants reach consensus?
  - justicz 8y ago
    You are right to call out the difference between "control" in the sense of keys and "control" in the sense of a network adversary. I should have been more careful with my wording there. It is true that if 35% of the participating stake is suddenly prevented from contacting the network, no new blocks will be created. The word "participating" is important -- you can have stake that is not participating in the agreement protocol, but that is still spendable. The only way I can think of to mitigate the scenario you've described would be this: before going offline, you can broadcast a transaction which essentially removes your stake from the pool of participating coins until you're able to come online again. This would ensure the network can proceed without you.
Vervious 8y ago
TBH I'd rather my assets be frozen, in the case of the network halting, than allow double spending, just because some honest players lost internet.
throwaway415415 8y ago
Yes people can duck with a network by cutting cables. This works with all internet protocols.
- thesausageking 8y ago
  If 99% of Bitcoin's hashrate gets taken off the internet, it keeps going without any problem. That's the beauty of a decentralized cryptocurrency. There's no central node and it's supremely fault tolerant. Algorand has a lot of interesting technology and may have some use cases. But it's more like a distributed database / voting system than a true cryptocurrency.
  - throwaway415415 8y ago
    That is not true. If network partitions happen in bitcoin you are utterly ducked. The system will fork and good luck to recover from that with all the double spendings.