# Technical Details of the Opcode Compatible zkEVM by Jordi Baylina | Devcon Bogotá

- Speakers: [Jordi Baylina](https://streameth.org/speakers/jordi-baylina)
- Channel: [Devcon](https://streameth.org/devcon)
- Date: 2023-10-07
- Duration: 25:10
- Watch: https://streameth.org/watch/yt-SIA5q2EEEGc
- YouTube: https://www.youtube.com/watch?v=SIA5q2EEEGc

## Description

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https://archive.devcon.org/archive/watch/6/technical-details-of-the-opcode-compatible-zkevm/

I will explain some technical details on how we, at PolygonHermez, built the opcode compatible zkEVM. This will include some design details of specific pieces like the storage, the arithmetic state machine, the keccak circuit, among others.  I will also go thru some snippets of the zkASM code that emulates the Ethereum VM.  
I will include in the talk some performance measures and I will do a live demo of the testnet.

Speaker(s): Jordi Baylina
Skill level: Advanced
Track: Layer 2s
Keywords: zkEVM,Zero Knowledge,rollup

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Devcon 6 was held in Bogotá, Colombia on Oct 11 - 14, 2022.
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## Transcript

foreign [Music] and today I'm going to present mainly the public test net that we publish it last last Monday first of all I'm going to explain a little bit how the ckvm works and then we are going to proceed to a demo works from the user perspective well a user should not see any much any any difference like working with any other network what we will do is first we will send uh transactions to a sequencer a sequencer we're already give a a state that means that the state will be final as far as you try as a sequencer sequencer the first version is going to be a centralized sequencer with the centralized later on but if you trust a sequencer this transaction is final and you have the warranty by the sequencer that this transaction is going to be mine it's going to be process it the sequencer will collect transactions and at some point we'll send these transactions to the blockchain okay and and then at this point the state is final and safe here we don't have any proof yet it's just the transactions are set and you have the warranty that those transactions are going to be processed uh in that order and because they are on chain you could they cannot they are not going to be changed so they you know that they are final and you don't need to trust the sequencer anymore you know that these transactions are final and in background in parallel it's going to be the proverb actually that's going to take all these transactions and it's going to compute it's going to prove that this implicit state so this is a state that's everybody can compute but it's not it's not Unchained because you know Chinese are only the transactions the data availability if you want the transactions are going to be processed but it's going to be converted to a rare to a real State and this is proved by the approver this is the big difference with the optimistic rollups in optimistic relapse you need to write for somebody to to challenge this state in the in you know in in a zero app this estate it's become the prover just set this state and you know for sure that this that that this is valid it's at this point where the user can withdraw with router funds so here the most important piece or the differential pipe is of a CK Roll Up is the proverb the proverb is a zero knowledge proof If you want a validity proof that uh validates the transactions which transactions ethereum transactions is taking a state is taking a set of infinity transactions and is Computing in your state and validating that this state is valid so how how the program is built so what's what's inside the approver well the approver is a set of Technologies but the way we build this we have a circuit with a traditional circuit written in in pill specific language we built for the ckvm that's mainly a processor it's a generic processor it's generic it's with some specifies that but it's a processor that's built with this zero knowledge uh technology and on top of this processor we are running a program we call it a ROM okay that actually is an ethereum it emulates ethereum it actually this program just is the is this problem is the one that is actually taking the transactions uh analyzing the transactions checking that the signatory is valid discounting the balances checking the fees deploying the smart contracts executing the smart contracts and doing exactly the same that does gaffer that doesn't mean ethereum node just processing this processing these transactions all this goes to approver and it's and this Brewery is the one that's verified on chain if you zoom in in the processor well we have a mainly a processor is this ZK processor it's a all these processor is very tailor made for uh the ckbm so it's not like a very generic processor it's this part that's generic but there are specific pieces that are made explicitly to be optimal for running the evm program the ckvm program okay this processor has a ram has a ROM which contains this program that's executed contains the storage because the ABM you should be able to store values and and and get the values it have also uh kind of a suit processor that handles all the binaries operations here includes addition subtraction and torque xores and so on has a model that's for identic this is you know in the in the in the IBM it works in 256 bits so this arithmetic circuit actually does all these operations in the 256 56 bits okay and then has uh the hashing for ketchups and other hashes that are also inside the inside the process inside this processor on top of this processor there is this ROM okay this ROM is written in assembly it's a specific assembly for this processor and here is what contains that this here contains all the logic actually what contains all the all the sodium logic that when we are processing here here I want to show you just a snippet of code of how this looks like this is just for example the the one and two but here we have all the opcodes we have implemented all the ethereum of codes uh at this point and then once we run this then we need like the cryptographic prover the cryptographic proverb uh what we do is mainly we are using Starks with a a very optimal way to compute proving systems we are using Goldilocks it's a technology for from people from for our colleagues in polygon 0 that makes to build these proofs really fast and it's again for recursion so it's approver can aggregate many proofs and at the end this is a stark and at the end what's doing is we are are converting we are very fine is a stark with a snark so at the end we just in ethereum we are just verifying a normal growth 16 or block uh proof it's just a circle it's a circum circuit in the last in the bottom of that piece so this is the stack the cryptographic stack for verifying that okay so let's cross fingers and let's try to see the demo let's see if it works if it doesn't work you can try it okay you can go to public.c kvm.test.net and fantastic you will see that's very simple the demo that I'm gonna do is first of all I'm gonna Bridge it let me just uh switch okay so the first thing that I'm going to do is I'm gonna I'm gonna Bridge uh so I mean go early uh I'm going to early Network I have an account here that's uh has three go early already and it's just a strike new account that I just created before this so the first thing that I'm going to do is I'm gonna transfer I'm gonna Bridge three ethers uh three uh well 0.25 first this is the maximum that we allow here in this test now just to protect some Daniel of service attacks here uh and we are just to transfer to the uh to the layer to the layers too so I mean go early right now so I'm just uh like let's see if ethereum works okay here we are uh let's Bridge it okay so let's sign let me just uh let me just let me just modify the gas fee so that it takes uh it goes faster let's go early so you never know save okay and then just send this transaction okay okay now that that no that so we just deposit the transaction this transaction is mining inwardly we need to White also a little bit so that this transaction is kind of a final so that this transaction is included okay right now it's this is already so it's this is already done what we have done is we just put this transaction in America tree and then the root of this migratory of all deposits is passed uh is passed as the as the state of the of the Roll Up the sequencer actually there has not been any trans any special transaction on chain because the sequencer already takes in account that okay so now let's uh finalize this okay and this finalize what is doing is collecting is doing an L2 transaction to collect these uh for these phones this ethereum in the in the layer two so here when I push here the first thing that I'll ask me is ask me is just to switch the network so I'm just switch the network and now I'm just signing the transaction in in and just on just signing the transaction in Layer Two okay because I just signed into transaction let's see if it works there we go shoot yeah here is okay so now if I check the account I'm in the layer two now I have the 0.25 ether in the layer in the layer two okay so now let's now let's go to do something with this account okay let's create a smart contract and deploy it in this layer too so let's go to remix just gonna use uh an example very simple smart contract [Music] looks like remix is gone so let's meet this little work yes it's just a very example smart contract so let me compile let me compile this smart contract there is and now I'm going to deploy it to the layer two so I'm going to connect this to a metamask okay I'm just using this account and then I'm just uh well this is I don't know if I'm connected to the last one well just connect here yeah this is the one that I just did I have the 25 feature here so and let's deploy this okay so just deploy this Mark on track it asked me to sign I just confirm this transaction see if it goes its internet is not like the fastest thing here but here is okay so now here we have the smart contract if we do a get a it's we get a zero but if we for example we set a 22 so this will generate a transaction to set this state variable to 22 we sign it confirm save there is and just get the value and I see here 22 right here okay so I just deployed that in layer 2 like any other network here okay so uh what's going on in here so let's let's see let's see the let's go to the let's go to the uh to the uh this is the roll up the smart contract in the layer one okay and here we see two kind of transactions one are the sequence uh batches like here where here you can see in the data that this is here all the all the transactions that we are setting okay but in parallel but in parallel to this we have the the batch the batches is the proverb that's generating batches that's actually validating these transactions and here is where all the magic happens okay here in the blockchain you cannot see much but here is the proof actually this is the grow 16 proof in this case that validates all the transactions that we have been processing processing ok so until here is well I can maybe I can give you a bonus bonus track here so we can go for example to UNI swap okay this unit is obviously is already deployed assist without compelling and recompiling anything it's just a normal unit swap it's deployed in Layer Two and here we can do for example a transfer let me just just change the account to the first one so that I have some some tokens to to exchange okay and here I want to compare from Full to Bar just a normal swap it's fetching the price and just doing the swap The Firm swap I should sign the transaction so here we have uh deploy it so we here we have already deployed the full uni swap but version 3 in the layer two and all this is verified in the program just confirm that okay now this is confirmed now here the the unit swap interface has some uh it's iterating takes maybe some 10 seconds or so to to realize that the transaction has been moved but that's mainly the thing okay so let me go well just let me see if it finished this okay so I already do the swap so I can just checking in swap just like normal like any other uh ethernet transaction so let me switch back to the presentation so nothing fancy right that's the cool thing and that's like strange things even for me explaining for me here I'm just feeling that I did a demo of ethereum but this is the interesting thing it's that the all this is running all this is validated in the Brewer all these transactions that are really complex or all the unit swap transactions and everything this is validated uh inside the broker and this is what this zkbm and the main importance of this design you don't have to recompile anything you just take the code exactly the same code you don't have to reality anything you don't have to learn anything you can use exactly the same tooling you can use the same the same language the same gas model it's no difference for developers they should not notice any difference in deploying in working with ethereum or in uh or in the KVM the only difference should be the gas price and the quantity of transactions that you should be able to deploy this is a test net please test it we have been running for this week already we have more than 1 000 accounts we have most of them are just deploying uh transactions some of the projects already tested uh already tested without any big issue we have some reports of some bugs that we haven't fixed also and we will continue work it's this testnet is a little bit like a baby it was worn last Monday but uh it's gonna get stronger and this is the the previous stage just to the to the to the main net okay here is uh okay and what's the limit of the scaling list we don't know yet what's clear is not gonna it's not gonna be in the proverb it's going to be maybe not that availability it's going to be in the maybe in the sequencer in the other pieces but because why because the proverb can be parallelized and here the important part actually for example we are running uh seven Brewers at this point because this week you know there is main transactions some of the products have been stopped so we are just just trying to catch up with the trend with some of these transactions but this is the cool thing we can run as many Proverbs as we want so if there is a lot of demand we're just running more Brewers and the only thing you need to take in account is what's a cost per transaction because running these servers are not free so what's it what's this cost well the cost right now is less than one cent per transaction and there is this is in AWS cost which is probably the the most expensive cloud service in the in the in the in the world and there is also a lot of optimizations that are coming here in GPU we can we believe that we can improve one order of magnitude and there is other improvements that we are working on that but proverb is not the is not the the bottleneck anymore what's missing well not much so we are fully compatible we are running all the all the all the off codes everything works as as ethereum is there are some things that we are already implementing they are not implemented yet and I'm just listening here but everything is there what is missing is that AIP is the original ethereum transactions this is mainly to deploy mainly not safe but it's uh just for for distance these smart contracts that have the same address in many in in in in many chains they use they are using these primitive transactions that they don't include the chain AV we are implementing those and then the we are not supporting yet the shadow 56 the Blake and the paintings pre-compile to Smart contracts but this is a work in progress all of them are doable and we will we will work in the upcoming on those on in the upcoming in the coming months there is the Audi Title One to enter an entertaining the Audi but this is probably the the most challenging part that we're facing right now there is a full plan for running this outage if anyone interested in that please contact me what else are we working on we are working also in aggregating of the proof right now the aggregators right now we are running one one proof per batch okay but we have to uh run one so we need to aggregate all these proofs in a single transaction and and with this in a single proof actually we're working in this proof this is not that much because we have all the recursion already done and it's just putting them together that's a piece that we need to put there and we're also working with AAP 4844 for line shelving this is uh clearly the future for the scalability and uh we already uh working uh on that we're very excited on that I I have to recognize that when I read this EIP I was very skeptical at the beginning but uh it's really the way to go we we can Implement insight and it really go will go even faster and it's even better that what I would what I would do it's just that you the only thing is that you need to go a little bit deep to understand this VIP that's really interesting I'm very excited for this gaming testing we're running the the ethereum test Suites right now we are at 97.7 97 of uh passing all these tests there are edge cases that we're still uh working on that but I'm sure that uh very soon uh we will be covering the will be in 100 of the of the ethereum of ethereum test roadmap of course we just launched the public test net uh we need to audit and we will launch when it's ready here is uh we want we want to be enough safe we want enough sure that so 100 uh safe is going to be impossible but we want we want to be responsible and we want to update this very well and when we feel comfortable then we will we will we will launch a reminder everything is open source you can take a look you can see you can you can review everything is uh in the GitHub repositories and yeah gkbm is no longer a myth foreign [Applause] thank you so much uh we have a couple of minutes for uh questions so if you have a question please raise your hand hello thank you for the presentation uh the AVM is not a frozen object it's leaving and it's evolving with new eips and we are going to see possibly big change like the eof or other things like that and they will be way easier to implement for core devs and for you so are you worried that some possible evm change will be hard to translate into circuits in the future uh we need to see which are those changes and once I see the changes I will tell you but there is one thing that because this is this is some of the the questions that I received now it is sometimes it's more about the upgradability of uh this what happened if the ckvm upgrade and then what happened with the roll up it will upgrade and if you want to decentralized system and but here is uh we need to understand as a community that uh the ABM at this point is evolving because it's work in progress but at some point this will this this will need to be frozen uh I don't know when and how but and I'm not talking about the ckvm I'm talking about the AVM so the ABM if you want uh I believe I I I I believe I hope and if talking with people with the effort they already think very much on that time is that at some point maybe in two years three years five years once the ethereum is finish it then the IBM will be Frozen and then it will be also the time to for to freeze the the roll-ups thank you for the presentation great talk I would like I mean could you detail a little bit what are the edge cases that you are meeting regarding the failing tests uh here we have uh Carlos in the room that's responsible for testing you can ask them but they are very very they are very very uh complex one it's a Carl of a static call and then do a surface truck and and do whatever you know this is our very very edge cases uh very very edge cases testing but you have to take you have to look at it because you never know one and it's important that's why those tests are are there but are really really edge cases at this point and complex ones hi thank you for the presentation uh when you were showing the uh on ethoscan the contents of the badge you showed like that there was like you know uh the code like encoded set of transactions is there any way to decode them uh to to see what exactly is in the batch yeah it's mainly many other transactions uh one after the other uh um we have some internal tooling just to to take a look on that well actually they are open source you can check the repositories but we are building it and in any case it would not be difficult to interpret at the end it's just a format with with the array of transactions I think we have time for one more question so if you can lend the microphone to our speaker ah cool go ahead hey thank you can you hear me yep okay um first of all congratulations this is amazing um when you launched let's suppose it's early next year obviously it's a very complicated system if you find some bug or something that needs to be addressed what can you do in that situation with the strapping decentralized systems is not uh is not an easy topic uh here we have the experience of Hermes 1.0 in our team and here you do some I would say nasty tricks uh here is maybe you do an upgradability things that you we can you can do is an upgrade so you can upgrade the smart contracts with maybe with a time lock and you can do for example is limit the the withdrawal the the withdrawal flow that's leaving the smart contract so that it's like if you are working with less as a certain amount you are purely decentralized but if you want to run fast and run bigger numbers then you can you have the option to go Central lights or just or or white until you you there are some tricks for Buddha strapping but this is our just temporary uh Solutions until we feel comfortable at some point the roll up should go along we are building on the centralized system and and it should be safe enough here is uh we are managing that in the in the in the in the beginning thank you so much Jersey valina please give him any thoughts [Applause]