6 ms·

Snowflake to Avalanche: A Novel Metastable Consensus Protocol Family for Crypto

92 points by pors 8y ago

woah 8y ago
Is this Sybil resistant though?
- simias 8y ago
  That's my question as well, the introduction says: > Specifically, the system operates by repeatedly sampling the network at random, and steering the correct nodes towards the same outcome. Obviously random sampling could be trivially manipulated if anybody can spawn nodes very easily. I expected that the "fix" would be in the "Snowflake" algorithm but I don't see how it prevents that: > When the protocol is correctly parameterized for a given threshold of Byzantine nodes and a desired guarantee, it can ensure both safety (P1) and liveness (P2). But isn't that threshold effectively infinite? If you look at something like the bitcoin network there are very few incentives to maintain full nodes. Meanwhile if having a majority of nodes let you cheat and steer the network (which is not the case for BTC thanks to PoW) the incentive to spawn a huge amount of byzantine nodes would be very high. After that the paper introduces the notion of "confidence" which might be the key to unraveling all that but I haven't yet fully understood that part. I don't have more time to look into it at the moment, hopefully somebody else will.
- KirinDave 8y ago
  You'd need to use this in a PoS style trusted set award. The internet couldn't scale to an arbitrarily sized fully connected, chatty network anyways.
aepiepaey 8y ago
Please update the submission title to match the title of the linked paper, i.e. "Cryptocurrencies" and not just "Crypto".
- jjallen 8y ago
  It's probably too long with the entire word.
  - nathell 8y ago
    Then maybe trim the initial catchphrase, or the word "novel."
- deleted 8y ago
  [deleted]
api 8y ago
This seems like a thoroughly thought out version of a DAG (directed acyclic graph) based currency. I don't have time to go through it with a fine toothed comb, but I'm curious about others' reactions. There are well known problems with DAGs: lack of incentive to run full nodes, tip choice attacks, flooding/spam attacks if there are no fees, and many and varied types of Sybil attacks. For flooding or spam a transaction proof of work isn't enough. Not only does it "waste" a lot of energy (though at the edge nodes where it's less visible than mining farms) which negates part of the purported benefit of a DAG, but it's vulnerable to ASICs or botnets. If you can short a cryptocurrency on any major exchange that supports short selling then it will get attacked with the goal not of stealing coins or censoring transactions but of just destroying it. Tip choice attacks combined with Sybil attacks can be very sophisticated. Tip choice is "random" but randomness cannot be verified. 3, 18, 593, 3, 3, now prove those were not random numbers modulus 1024. You can't of course. So I can non-randomly choose the transactions I link to. If I combine this with some sophisticated analysis of the network's transaction structure and physical topology I might be able to skew the network in some disastrous way over time in ways that would be completely undetectable since my apparently "random" tip/link choices were not in fact random. Then I can do something like short the coin and do something nasty to the network. Attackers can be very very creative, and attacks only get better. Last but not least: there is no mining mechanism in a DAG coin, or at least I've never heard of how one could be done. This means DAG coins are "Big Bang" coins that begin with all the money that will ever exist. This is problematic from an economic point of view and opens a huge can of worms around what is done with that money and how it is distributed to initial holders.
jchook 8y ago
Perhaps this is the technology behind https://chia.net https://chia.net ?
- paulsutter 8y ago
  Chia is bitcoin but with farming (storage) instead of mining (compute), plus a whole host of cleanups to do it right. So no DAG or any such thing. One could read "Beyond Hellman's Time-Memory Trade-Offs with Applications to Proofs of Space" https://eprint.iacr.org/2017/893.pdf https://eprint.iacr.org/2017/893.pdf
  - api 8y ago
    Is proof of space actually "greener" than proof of work? Memory and hard drives consume power, and querying them consumes power. Seems like it could be just another kind of work. It would be more ASIC resistant though.
    - paulsutter 8y ago
      yes. vastly.
      - api 8y ago
        I'm curious about this. Are you saying that relying on storage latency and volume is energetically cheaper than relying on compute? I see a few flaws in this. First of all: all fast storage media consume energy even when idle. Secondly I think this neglects the embodied energy (energy to manufacture) of storage media. Lastly if a proof of storage mining scheme became popular you'd probably see ASICs that incorporate onboard fast memory controllers with huge caches and other approaches that would improve performance to the point that this would just become another proof of work. Comparing full life cycle energy of different approaches to securing a cryptocurrency is actually pretty tough. It's also pretty hard to compare it to the energy requirements of more conventional approaches to currency since the energy cost of those is so spread out across society.
    - 8y ago
mkirklions 8y ago
At this point, are these papers simply to reduce the cost of verification? It seems thats the only problem in the crypto world, but I dont know if verification will ever be scalable.
- simias 8y ago
  What do you mean about "cost of verification"? Verification is not too difficult, it's reaching a consensus among trust-less nodes that is. PoW solves the problem by making it so that any node which receives two valid but conflicting versions of blockchain has an objective metric to decide which one is the "right" one. The answer being whichever has the most work put into it. Since you can't fake work you can't arbitrarily create a new chain that would take over the others (unless you manage to work harder than all the rest of the network combined, hence the 51% attacks). Without PoW if you receive two valid but conflicting chains you need an other metric to decide which one you select. This paper describes such an approach.
  - stri8ed 8y ago
    Verification becomes difficult, when the system gains adoption and processes thousands of TX per second. Then the issue becomes about the trade-off between node resource requirements, and decentralization. Fundamentally, every node having to process/verify every single transaction in the network,is not scalable.
    - SkyMarshal 8y ago
      Hence the ongoing debate around whether verification should be less computationally costly than computation (BTC) or whether a system can be architected to successfully scale even when verification == computation (ETH).
apo 8y ago
Initial reactions: 1. Sybil-resistance (faking strong consensus by deploying cheap replica nodes you control) in a protocol like this is crucial. All I could find is this: To prevent Sybil attacks, it uses a mechanism like proof-of-stake that assigns weights to participants in committee selection based on the money in their accounts. 2. Every non-proof-of-work protocol I've seen, including Ripple Consensus Process and proof-of-stake creates a problem of initial coin distribution. PoW systems have a clean distribution mechanism based on external resource consumption. Non-PoW systems produce an airdrop situation. Players start with no funds, and so can't stake. The creator of the network manually assigns ownership, with important long-term political consequences (e.g., Ripple). 3. The lack of an incentive structure around fees in protocols like Ripple creates bizarre economic consequences. For example, Ripple is guaranteed to lose money stock because fees are simply burned, rather than given to the consensus leader as in Bitcoin. 4. So far, I haven't seen anything in the paper regarding denial of service attacks on nodes. In other words, I see no negative incentives levied on those who can sign transactions from flooding the network with useless spam, bogging everything down.
- shepardrtc 8y ago
  > PoW systems have a clean distribution mechanism based on external resource consumption. Unless the creators are the only ones mining for a time.
  - apo 8y ago
    True, this has been one of the consistent criticisms of Bitcoin - Satoshi solo mined coins and therefore distribution wasn't fair. OTOH, consider the alternative. Satoshi gave himself all the money in the system, then divvied it up among his friends. However, given the availability of multiple multi-billion dollar cryptocurrency economies, another option might be possible. Airdrop to the current holders of some other cryptocurrency. Or maybe a basket of cryptocurrencies. Key owners could then claim their money on the newly-created network. This idea really started to take off in 2018 with Bitcoin hard forks. The problem is that the network creator will face intense pressure to withhold just a little currency to fund a war chest. Yielding to that pressure creates the very political problems I alluded to earlier (e.g., Ethereum).
chrispeel 8y ago
It would be good if the authors would have extended figures 20, 21, and 22 out to networks of size 20,000 or more nodes. Or at least described what they expect to happen. I.e. if you have many more nodes, does the throughput remain above 1k tps? I also always like authors who are willing to acknowledge the limitations of their work. If this work described the limitations I didn't see it; maybe they think there are none :-)
- wyas 8y ago
  Cursory reading, they do seem to discuss limitations. They say that the system is not guaranteed to provide liveness for double-spends.
blattimwind 8y ago
Either "using crypto" or "for cryptocurrencies"
leijurv 8y ago
This sounds an awful lot like each transaction can consume exactly one UTXO, but can have multiple UTXO outputs. This would cause progressive "shattering" of the UTXO set into millions of low-value "dust" UTXOs, a problem that Bitcoin is struggling with (specifically, how best to incentivize "cleaning up" the UTXO set by making transactions with multiple inputs, even though that increases the overall transaction size). "We adopt what is commonly known as Bitcoin’s unspent transaction output (UTXO) model. In this model, clients are authenticated and issue cryptographically signed transactions that fully consume an existing UTXO and issue new UTXOs."
- leijurv 8y ago
  It seems like in this protocol, such a cleanup wouldn't even be possible... if transactions can have only one input
- wyas 8y ago
  Seems like ambiguous wording on that part. However, they do not seem to require single-UTXO-inputs, but can consume multiple.
just_one_time_ 8y ago
I am loving watching you idiots try to catch up with crypto now. For years I tried to post about Bitcoin here only to be ridiculed. Fuck you guys.
baby 8y ago
We’re a technical community. Can we not shorten cryptocurrencies to crypto? Admin can you change the title?
douglaswlance 8y ago
Do you think it would be possible to build a consensus algorithm for scientific consensus?
3721 8y ago
Much like hashgraph https://hederahashgraph.com https://hederahashgraph.com

92 points by pors 8y ago

woah 8y ago

Is this Sybil resistant though?

simias 8y ago
That's my question as well, the introduction says: > Specifically, the system operates by repeatedly sampling the network at random, and steering the correct nodes towards the same outcome. Obviously random sampling could be trivially manipulated if anybody can spawn nodes very easily. I expected that the "fix" would be in the "Snowflake" algorithm but I don't see how it prevents that: > When the protocol is correctly parameterized for a given threshold of Byzantine nodes and a desired guarantee, it can ensure both safety (P1) and liveness (P2). But isn't that threshold effectively infinite? If you look at something like the bitcoin network there are very few incentives to maintain full nodes. Meanwhile if having a majority of nodes let you cheat and steer the network (which is not the case for BTC thanks to PoW) the incentive to spawn a huge amount of byzantine nodes would be very high. After that the paper introduces the notion of "confidence" which might be the key to unraveling all that but I haven't yet fully understood that part. I don't have more time to look into it at the moment, hopefully somebody else will.
KirinDave 8y ago
You'd need to use this in a PoS style trusted set award. The internet couldn't scale to an arbitrarily sized fully connected, chatty network anyways.

aepiepaey 8y ago

Please update the submission title to match the title of the linked paper, i.e. "Cryptocurrencies" and not just "Crypto".

jjallen 8y ago
It's probably too long with the entire word.
- nathell 8y ago
  Then maybe trim the initial catchphrase, or the word "novel."
deleted 8y ago
[deleted]

api 8y ago

This seems like a thoroughly thought out version of a DAG (directed acyclic graph) based currency. I don't have time to go through it with a fine toothed comb, but I'm curious about others' reactions. There are well known problems with DAGs: lack of incentive to run full nodes, tip choice attacks, flooding/spam attacks if there are no fees, and many and varied types of Sybil attacks. For flooding or spam a transaction proof of work isn't enough. Not only does it "waste" a lot of energy (though at the edge nodes where it's less visible than mining farms) which negates part of the purported benefit of a DAG, but it's vulnerable to ASICs or botnets. If you can short a cryptocurrency on any major exchange that supports short selling then it will get attacked with the goal not of stealing coins or censoring transactions but of just destroying it. Tip choice attacks combined with Sybil attacks can be very sophisticated. Tip choice is "random" but randomness cannot be verified. 3, 18, 593, 3, 3, now prove those were not random numbers modulus 1024. You can't of course. So I can non-randomly choose the transactions I link to. If I combine this with some sophisticated analysis of the network's transaction structure and physical topology I might be able to skew the network in some disastrous way over time in ways that would be completely undetectable since my apparently "random" tip/link choices were not in fact random. Then I can do something like short the coin and do something nasty to the network. Attackers can be very very creative, and attacks only get better. Last but not least: there is no mining mechanism in a DAG coin, or at least I've never heard of how one could be done. This means DAG coins are "Big Bang" coins that begin with all the money that will ever exist. This is problematic from an economic point of view and opens a huge can of worms around what is done with that money and how it is distributed to initial holders.

jchook 8y ago

Perhaps this is the technology behind https://chia.net https://chia.net ?

paulsutter 8y ago
Chia is bitcoin but with farming (storage) instead of mining (compute), plus a whole host of cleanups to do it right. So no DAG or any such thing. One could read "Beyond Hellman's Time-Memory Trade-Offs with Applications to Proofs of Space" https://eprint.iacr.org/2017/893.pdf https://eprint.iacr.org/2017/893.pdf
- api 8y ago
  Is proof of space actually "greener" than proof of work? Memory and hard drives consume power, and querying them consumes power. Seems like it could be just another kind of work. It would be more ASIC resistant though.
  - paulsutter 8y ago
    yes. vastly.
    - api 8y ago
      I'm curious about this. Are you saying that relying on storage latency and volume is energetically cheaper than relying on compute? I see a few flaws in this. First of all: all fast storage media consume energy even when idle. Secondly I think this neglects the embodied energy (energy to manufacture) of storage media. Lastly if a proof of storage mining scheme became popular you'd probably see ASICs that incorporate onboard fast memory controllers with huge caches and other approaches that would improve performance to the point that this would just become another proof of work. Comparing full life cycle energy of different approaches to securing a cryptocurrency is actually pretty tough. It's also pretty hard to compare it to the energy requirements of more conventional approaches to currency since the energy cost of those is so spread out across society.
  - 8y ago

mkirklions 8y ago

At this point, are these papers simply to reduce the cost of verification? It seems thats the only problem in the crypto world, but I dont know if verification will ever be scalable.

simias 8y ago
What do you mean about "cost of verification"? Verification is not too difficult, it's reaching a consensus among trust-less nodes that is. PoW solves the problem by making it so that any node which receives two valid but conflicting versions of blockchain has an objective metric to decide which one is the "right" one. The answer being whichever has the most work put into it. Since you can't fake work you can't arbitrarily create a new chain that would take over the others (unless you manage to work harder than all the rest of the network combined, hence the 51% attacks). Without PoW if you receive two valid but conflicting chains you need an other metric to decide which one you select. This paper describes such an approach.
- stri8ed 8y ago
  Verification becomes difficult, when the system gains adoption and processes thousands of TX per second. Then the issue becomes about the trade-off between node resource requirements, and decentralization. Fundamentally, every node having to process/verify every single transaction in the network,is not scalable.
  - SkyMarshal 8y ago
    Hence the ongoing debate around whether verification should be less computationally costly than computation (BTC) or whether a system can be architected to successfully scale even when verification == computation (ETH).

apo 8y ago

Initial reactions: 1. Sybil-resistance (faking strong consensus by deploying cheap replica nodes you control) in a protocol like this is crucial. All I could find is this: To prevent Sybil attacks, it uses a mechanism like proof-of-stake that assigns weights to participants in committee selection based on the money in their accounts. 2. Every non-proof-of-work protocol I've seen, including Ripple Consensus Process and proof-of-stake creates a problem of initial coin distribution. PoW systems have a clean distribution mechanism based on external resource consumption. Non-PoW systems produce an airdrop situation. Players start with no funds, and so can't stake. The creator of the network manually assigns ownership, with important long-term political consequences (e.g., Ripple). 3. The lack of an incentive structure around fees in protocols like Ripple creates bizarre economic consequences. For example, Ripple is guaranteed to lose money stock because fees are simply burned, rather than given to the consensus leader as in Bitcoin. 4. So far, I haven't seen anything in the paper regarding denial of service attacks on nodes. In other words, I see no negative incentives levied on those who can sign transactions from flooding the network with useless spam, bogging everything down.

shepardrtc 8y ago
> PoW systems have a clean distribution mechanism based on external resource consumption. Unless the creators are the only ones mining for a time.
- apo 8y ago
  True, this has been one of the consistent criticisms of Bitcoin - Satoshi solo mined coins and therefore distribution wasn't fair. OTOH, consider the alternative. Satoshi gave himself all the money in the system, then divvied it up among his friends. However, given the availability of multiple multi-billion dollar cryptocurrency economies, another option might be possible. Airdrop to the current holders of some other cryptocurrency. Or maybe a basket of cryptocurrencies. Key owners could then claim their money on the newly-created network. This idea really started to take off in 2018 with Bitcoin hard forks. The problem is that the network creator will face intense pressure to withhold just a little currency to fund a war chest. Yielding to that pressure creates the very political problems I alluded to earlier (e.g., Ethereum).

chrispeel 8y ago

It would be good if the authors would have extended figures 20, 21, and 22 out to networks of size 20,000 or more nodes. Or at least described what they expect to happen. I.e. if you have many more nodes, does the throughput remain above 1k tps? I also always like authors who are willing to acknowledge the limitations of their work. If this work described the limitations I didn't see it; maybe they think there are none :-)

wyas 8y ago
Cursory reading, they do seem to discuss limitations. They say that the system is not guaranteed to provide liveness for double-spends.

blattimwind 8y ago

Either "using crypto" or "for cryptocurrencies"

leijurv 8y ago

This sounds an awful lot like each transaction can consume exactly one UTXO, but can have multiple UTXO outputs. This would cause progressive "shattering" of the UTXO set into millions of low-value "dust" UTXOs, a problem that Bitcoin is struggling with (specifically, how best to incentivize "cleaning up" the UTXO set by making transactions with multiple inputs, even though that increases the overall transaction size). "We adopt what is commonly known as Bitcoin’s unspent transaction output (UTXO) model. In this model, clients are authenticated and issue cryptographically signed transactions that fully consume an existing UTXO and issue new UTXOs."

leijurv 8y ago
It seems like in this protocol, such a cleanup wouldn't even be possible... if transactions can have only one input
wyas 8y ago
Seems like ambiguous wording on that part. However, they do not seem to require single-UTXO-inputs, but can consume multiple.

just_one_time_ 8y ago

I am loving watching you idiots try to catch up with crypto now. For years I tried to post about Bitcoin here only to be ridiculed. Fuck you guys.

baby 8y ago

We’re a technical community. Can we not shorten cryptocurrencies to crypto? Admin can you change the title?

douglaswlance 8y ago

Do you think it would be possible to build a consensus algorithm for scientific consensus?

3721 8y ago

Much like hashgraph https://hederahashgraph.com https://hederahashgraph.com