I think the later makes sense (once we are there), but remember that there will never be a single Plasma spec, Plasma is more of a design philosophy/set of guidelines.
Yes, and it’s kind of concerning if one of those projects actually goes live (although I think chances are slim, they just want to grab naive investors’ money). Then it could make some mess and damage the reputation of Plasma. That’s why I think the Eth community will/should discuss and review such projects (one of the reasons I’ve asked you to name them).
All Plasma designs have vulnerabilities or at least specific UX tradeoffs that need to be addressed. Some companies put a PoS model on top and claim a kind of “security by obscurity”. These companies need to be called out.
I’d leave Vitalik and EF out of it, as their involvement has allowed for the Plasma-hype in the first place. Rather I suggest to define the requirements that a spec would need to satisfy to be considered ready for “production”.
Ultimately, any Plasma design will have to prove itself in production deployment.
Congratulations for your upcoming fund raising. Your SKALE Network seems like EVM-ecosystem scaling solution. And I personally guess the withdrawal procedure will be done by ParityBridge-like somehow trusted(federated) withdrawal module.
But I’ve seen this article and it says “SKALE will be the first implementation of the Ethereum Virtual Machine (EVM) on a Plasma chain”.
So there is quite a bit of confusion that SKALE is EVM Plasma, but sounds like it has exit mechanism. Do you plan to use expensive EVM inside EVM construction? Or, is it Plasma?
@sg - thank you for your message and congratulations on the fund raise! There has been admittedly a bit of confusion in the way we got described in the press. We do not consider ourselves Plasma. In my humble opinion Plasma is a very specific thing which includes a Plasma operator that operates an UTXO chain as well as a set of exit algorithms that are executed if the Plasma operator becomes malicious.
At Skale we are building a network of ETH-compatible side chains that use fast PoS-like consensus. Miners will be able to add servers to our network and stake Skale tokens to make money. Out of this large network of servers we will be able to build side-chains on demand by randomly picking servers, and then rotating them from time to time. A dapp developer will be able to pay in Skale tokens and get a side chain for her application.
Nowadays for some people (including investors) Plasma is more of a generic term everything that speeds up transactions If they want to keep calling us Plasma, we do not really argue too much … ))
It looks like OmiseGo is the leader in terms of Plasma implementation on the moment. For me OmiseGo are the good guys, in a sense that they are trying to make things secure.
So in this spec, what happens if I start with a $100 UTXO, and do a 100,000 transactions sending 1 cent to myself (to my other address).
I then randomly pick out of these transactions 1000 spent UTXOs and try to fraudulently exit all of them.
How does this work in case of OmiseGO? Who is going to be the party challenging the exits and how is this party going to be paid?
User must put up a bond on each exit, challenger receives that bond for a successful challenge. Slight oversimplification of the solution but that’s the basic idea. Incentives should be aligned such that people will just challenge stuff because it’s worthwhile to do so.
Where’d you get $900 from for the other 90,000 transactions?
With plasma cash, you can create 10,000 tokens from this $100 and then you just submit proofs of inclusion / exclusion when it comes time to exit. Anyone can challenge an exit, but in the case of you sending coins to yourself, there doesn’t seem to be any reason for anyone to challenge given that you’re only touching your own collateral.
Understood - thank you. I think the next step is to provide a formula for the value of the bond. It should probably be proportional to the amount being exited.
Thats the problem - you are creating lots of spent UTXOs that you can try fraudulently exit by claiming them unspent - what Kelvin says is that for every exit the person exiting is supposed to post a bond which serves as an incentive for bounty hunters to catch fraudulent exit attempts.
There is another difficult problem, which also needs to be addressed somehow. Lets say the operator becomes malicious and everyone attempts to exit the system.
Due to performance restrictions of the main chain, one will probably be able to have no more than one exit per second without significantly affecting the gas prices.
This means 3600 * 24 * 7 = 100,000 exits maximum in a week.
Therefore, each Plasma operator should(?) be limited to having 100,000 coins maximum unless batch exits are implemented.
May be a way to solve this is to require multiple Plasma operators and limit each of them to 100,000 coins. Then there has been
It is a hard problem, I hope it will be solved somehow …
Does this include an exit bond similar to OmiseGO implementation? I think it does, but does not specify the value of the bond. It should probably be linearly proportional to the amount exited.
In the case where exits from self-transfer transactions are challenged, the challengers need to potentially have a copy of the entire Plasma chain, which may be terabytes of information. This needs to be discussed I think. The Plasma operator needs to provide to the bounty hunters a way to continuously download the entire chain.
In the example where Alice creates a chain of 1M self-transfer transactions and attempts to fraudulently exit some of these transactions, there are no counterparties that will care about storing the proof of Alice spending the transactions.
Therefore, the only party that will be able to challenge Alice will be the Plasma operator itself, or the bounty hunters. But bounty hunters will need to have an up-to-date copy of the entire chain.
The funny thing is that if, say, there are 10 bounty hunters that have to maintain a copy of the entire chain, it is almost like having a PoA chain where there is one block producer and 10 slaves.
Unfortunately the paper does not go into detail on that topic and it’s not discussed as a possible attack. However, I could imagine that this part also solves for the attack you describe:
Starting an exit for a coin requires providing the transaction that gave the exitor owner- ship of the coin signed by the previous owner in the coin’s history, as well as a direct ancestor of that transaction.
I haven’t had much time to think about it, but could it be forbidden to exit a coin that you sent to yourself in the parent transaction?
Why do you believe bond pricing should depend on the amount being exited?
Creating a chain of 1m self transfer transactions in Plasma Cash is just Alice having a certain coin and spending it over 1m blocks to herself. At any given point if she attempts to exit at an earlierpoint than the latest spend, her exit can be challenged with a direct spend of it. No need to store the whole tx history. The challenge is just 1 merkle branch (+signatures obviously) which proves that the coin being exited has been spent.
Plasma Cash is not vulnerable to any of the attacks you describe, exactly because each coin is unique and independent from each other.
Actually we are discussing Plasma MVP and not Plasma Cash ) OmiseGo spec we started to discuss above it Plasma MVP. The same is as a understand true for Loom Network.
So for Plasma MVP, if I have a long set of transactions sending money to myself, then no-one except myself cares about these transactions.
This means that if I try to fraudulently exit some of the spent UTXOs, I will have no counterparty to challenge this, since I was both the sender and the receiver.
So the only one to challenge me will be “bounty hunters” who just want to make money from my deposit.
Do other people on this thread agree to this point of view?
If I am a bounty hunter, I need to have a copy of the entire chain since fraudulent exits may come from anywhere in the chain.
At 1000 transactions per second, a chain will produce 6 TB a year. This means that a bounty hunter will need to run a Hadoop or Spark cluster to verify exits. You wont be able to do it on a PC.
Getting the economics right for the bounty hunters will be super important. If they are only paid when they find fraudulent exits, the question will be to have enough fraudulent exits to support the hunters.
Lets say I want to become a full time bounty hunter and run a Spark cluster to catch bad guys. I will probably want to make $200K a year and also pay for the cloud costs. The question is, how I am I going to make this $200K a year if I am only paid when someone does fraudulent exit attempts and I catch them ? The better job I do, the less fraudulent exits will be attempted, the less money I will make.
May be the Plasma operator needs to do some mockup fraudulent exits to feed the bounty hunters?))
It is a very rough estimate. Eth is able of < 20 TPS in general. You do not want to take more than 10% of the overal transactions, otherwise the gas price will skyrocket.
I totally agree on that. It looks like without mass exits the spec should limit the number of coins (UTXOs) a chain can hold . But then frankly, if you limit you chain to 100,000 coins it may not be useful at all unless it is used to serve population of in a small town.
I’m not sure that’s true. It limits the rate at which you can conduct entries and exits, but you can take however long to conduct an exit and have a pretty good guarantee that it will still be there when you’re ready to exit. A mass exit will be annoying and take a very long time, but it doesn’t have a deadline and thus shouldn’t limit the size of the underlying network.
The rate of entry controls the growth of the network, not the amount of coins possible to trade. There is a larger limit on the coins related to the choice of tree depth and data availability solutions, but I would think this is generally much higher than 100k tokens.
You’re talking about exiting 100,000 coins, but nobody is even discussing how to get all those users onboarded to begin with, in the first place! How did all those users get there? Do you know how long it would take to onboard 100k unique users to the plasma chain with the current constructs that we have at present?
This is why mass transfers should exist where one party enters with a large piece of collateral and then fragments it amongst 100k users. But even in this case, that’s just a credit plasmachain - actually reimbursing the operator for all of this is another story which will likely be supported by FIAT.
@kfichter - how do you throw away things older than two weeks ? You could have an open UTXO which is in a very old block (e.g. one year old). What procedure do you use for check pointing? It is not clear to me how this could be done on an UTXO chain.
And, does check-pointing mean trusting the chain operator in some way?