5 ms·

I'm still reading the paper, but I'm not seeing any discussion of a sybil or eclipse attack defense.

by Rhapso 12y ago

burke 12y ago
This is kind of explained away implicitly by pages 6-7. Each node has its own quorum slice, and they tend to point upward to a set of trustworthy financial institutions, not entirely unlike DNS. i.e. FBA relies on a web of trust, not just on showing up and churning out hashes or whatever.
- TheOsiris 12y ago
  isn't this still sort of pseudo-centralized? my guess is that most people will trust the same handful of nodes.
  - r721 12y ago
    It's interesting how this suddenly shifts into "journalistic independence" territory - what about who reports on that? What if some influential source would receive some financial aid for proper reporting?
  - JoelKatz 12y ago
    This kind of "pseudo-centralized" is decentralized. When the "central authority" gets all of its power from individual participants who choose to follow it, and those participants are free to change the authorities at any time, that's a decentralized model. Bitcoin isn't centralized just because everyone has to agree on which transactions are valid.
mjb 12y ago
Read section 3 and 4 of the whitepaper - the whole trust a quorum model is directly aimed at Sybil-style attacks. The key argument here is that the way they do group membership prevents these attacks by using a trusted quorum. This seems like a key place to focus attention for outside analysis of the properties of this protocol. If the assertions about this are incorrect, then the whole thing breaks down. As the Sybil paper points out, membership is critical for consensus. As a common-sense thing, "we have agreed" is super dependent on who "we" is. As for eclipse, the model is so fundamentally different that it's not clear that there is a direct analogy for those network attacks. What do you have in mind? I'm not saying that it's obviously safe, just that attacks on the network protocol would have a very different flavor.
spolu 12y ago
(disclaimer: I had early access to the white paper for review) Sybil attacks are not really directly applicable here since each node in the system picks its own quorum slices (basically the set of nodes that it trusts). There is no notion of global reputation and nodes do not need to know every other nodes to participate. Looking at the definition of quorum intersection[0] section 4.1 should give you a sense of the conditions that are required on the choice of quorum slices for the network to function properly (quorum intersection ensures safety) The proof exposed in the paper guarantees safety and liveness for the network provided a certain number of reasonable conditions are held true. What that means is that an attacker cannot force on intact nodes (definition p14) invalid transactions nor prevent the network from making progress. That being said, (at least in the version I reviewed) there is no guarantee provided with respect to ensuring that all valid transaction will eventually make it into the network. Indeed a set of highly trusted nodes (present in a lot of quorum slices) could attempt to preempt a specific set of transactions X (originated by edge nodes) by opportunistically broadcasting valid transaction set V_i for each successive ledger entry i that explicitly do not include the targeted set of transactions X. Under raw SCP as described in the paper and for certain topologies this preemption could be real and this is the closest I can think of a Sybil attack. It's important to note that we still have liveness and safety in that case. I believe the same kind of attacks to be plausible with the Bitcoin network and I know protection mechanisms against it are currently being evaluated by David, Jed and the rest of the team. I will let them share their progress when they think it's right. I also hope they will correct me if I stated anything inaccurate here! [0] https://www.stellar.org/papers/stellar-consensus-protocol.pdf https://www.stellar.org/papers/stellar-consensus-protocol.pd...
- nullc 12y ago
  > I believe the same kind of attacks to be plausible with the Bitcoin network This isn't anyone elses understanding. Can you suggest a mechanism by which it would be possible for a minority conspiracy to perpetually exclude a transaction in Bitcoin?
  - spolu 12y ago
    Well in bitcoin, of course, trust would map to computing power.

I'm still reading the paper, but I'm not seeing any discussion of a sybil or eclipse attack defense.

by Rhapso 12y ago

I'm still reading the paper, but I'm not seeing any discussion of a sybil or eclipse attack defense.

burke 12y ago

This is kind of explained away implicitly by pages 6-7. Each node has its own quorum slice, and they tend to point upward to a set of trustworthy financial institutions, not entirely unlike DNS. i.e. FBA relies on a web of trust, not just on showing up and churning out hashes or whatever.

TheOsiris 12y ago
isn't this still sort of pseudo-centralized? my guess is that most people will trust the same handful of nodes.
- r721 12y ago
  It's interesting how this suddenly shifts into "journalistic independence" territory - what about who reports on that? What if some influential source would receive some financial aid for proper reporting?
- JoelKatz 12y ago
  This kind of "pseudo-centralized" is decentralized. When the "central authority" gets all of its power from individual participants who choose to follow it, and those participants are free to change the authorities at any time, that's a decentralized model. Bitcoin isn't centralized just because everyone has to agree on which transactions are valid.

mjb 12y ago

Read section 3 and 4 of the whitepaper - the whole trust a quorum model is directly aimed at Sybil-style attacks. The key argument here is that the way they do group membership prevents these attacks by using a trusted quorum. This seems like a key place to focus attention for outside analysis of the properties of this protocol. If the assertions about this are incorrect, then the whole thing breaks down. As the Sybil paper points out, membership is critical for consensus. As a common-sense thing, "we have agreed" is super dependent on who "we" is. As for eclipse, the model is so fundamentally different that it's not clear that there is a direct analogy for those network attacks. What do you have in mind? I'm not saying that it's obviously safe, just that attacks on the network protocol would have a very different flavor.

spolu 12y ago

(disclaimer: I had early access to the white paper for review) Sybil attacks are not really directly applicable here since each node in the system picks its own quorum slices (basically the set of nodes that it trusts). There is no notion of global reputation and nodes do not need to know every other nodes to participate. Looking at the definition of quorum intersection[0] section 4.1 should give you a sense of the conditions that are required on the choice of quorum slices for the network to function properly (quorum intersection ensures safety) The proof exposed in the paper guarantees safety and liveness for the network provided a certain number of reasonable conditions are held true. What that means is that an attacker cannot force on intact nodes (definition p14) invalid transactions nor prevent the network from making progress. That being said, (at least in the version I reviewed) there is no guarantee provided with respect to ensuring that all valid transaction will eventually make it into the network. Indeed a set of highly trusted nodes (present in a lot of quorum slices) could attempt to preempt a specific set of transactions X (originated by edge nodes) by opportunistically broadcasting valid transaction set V_i for each successive ledger entry i that explicitly do not include the targeted set of transactions X. Under raw SCP as described in the paper and for certain topologies this preemption could be real and this is the closest I can think of a Sybil attack. It's important to note that we still have liveness and safety in that case. I believe the same kind of attacks to be plausible with the Bitcoin network and I know protection mechanisms against it are currently being evaluated by David, Jed and the rest of the team. I will let them share their progress when they think it's right. I also hope they will correct me if I stated anything inaccurate here! [0] https://www.stellar.org/papers/stellar-consensus-protocol.pdf https://www.stellar.org/papers/stellar-consensus-protocol.pd...

nullc 12y ago
> I believe the same kind of attacks to be plausible with the Bitcoin network This isn't anyone elses understanding. Can you suggest a mechanism by which it would be possible for a minority conspiracy to perpetually exclude a transaction in Bitcoin?
- spolu 12y ago
  Well in bitcoin, of course, trust would map to computing power.