Hyperledger Foundation Meetups, 24 Nov 2021

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From YouTube: Atomic cross chain swap between Hyperledger Fabric and Ethereum

Description

A virtual meetup hosted by Hyperledger Budapest on November 24, 2021 featuring Daniel Szego. During this presentation and hands on he will investigate the theoretical and technical possibilities for realizing atomic cross chain swaps between Hyperlegder Fabric and Ethereum. We will cover some of the theoretical background of the field, like hashed timelock contracts and atomic cross chain swap algorithms. We will also demonstrate an experimental implementation for such a swap between Hyperlegder Fabric and Ethereum Ropsten test network.

More about this meetup is at: https://www.meetup.com/Hyperledger-Budapest/events/280859820/

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A

Okay, you're live so.

B

Then hello, everybody or good afternoon good morning, I'm I'm not quite sure about the time. uh So this is high. This is hyperledger meetup. uh I'm gonna have basically um like a brief presentation or a sh or a short workshop uh on atomic cross chain swaps.

B

uh Today, uh there's there's gonna be one one example: that's having like an atomic cross chain swap between hyperledger affair being and and and ethereum, um I'm not quite sure if if people are still coming, uh but I would slowly actually start by introducing step by step just the beginnings I mean just the just the introductory stuffs, uh so perhaps perhaps people still still coming. Basically, uh I think it's gonna be like one hour uh and sometimes my internet connection is not always the best.

B

So if I just get you know very much as a robot, uh then it might happen for for a second or two, but I hope it's it's gonna work. I I don't share myself. Basically uh on a video. uh On the one hand, uh it's because.

A

I have been working.

B

In home office for a while, so I I don't look very much, you know I mean I mean uh as a sales people. um On the other hand, I mean, if I just uh if I just have my video running, then basically I my my connection- will be even more chappy. um So basically, let me just start.

B

This is the agenda for today again, uh it's it's not gonna, be something as a ready to go tool. What I'm presenting today, uh but it will be a demonstration how you can do like hash or how you can implement like hashtag contracts or atomic cross chain swaps uh between between each between different blockchains, um especially between like ethereum and hyperledger fabric. So what I'm gonna do today uh as an agenda, I will just try to introduce step-by-step the concept of atomic cross chain swaps and hash timelock contracts.

B

So basically, I will start somehow with the problem statement. uh What's the problem, so why? Why do we need this whole stuff at all? uh We just this guy. Basically, the basic building blocks. That's that's the hashtag contract hdic uh based on two hdlc. We can do an atomic cross chain swap so basically it's it's something again that I'm gonna demonstrating.

B

I have one example: implementation, as well uh as the title of the presentation says it's an it's: an implementation of foreign for an atomic cross chain swap between between hyper ledger fabric and ndtu.

B

So there will be some some demonstrations both for the swaps and basically uh uh for for the for the individual htlc's as well. uh So this will be like like two demonstrations and at the end I will just list some some practical considerations.

B

So that's the agenda for today uh and at the end we can have like a longer discussion.

B

If you have like you know, I mean shorter questions in the middle or, if you, if you don't understand anything or if my voice is getting very choppy or on my connection unstable, then just interrupt me and then I try to answer uh or or somehow, repair the technical problems as soon as I can, or as fast as as fast as I can. But if, if we have like you know like like longer considerations or longer discussions, then I would propose to have it have it somehow.

B

At the end, I will have one uh demonstration code as well: it's it's in a github repo. uh It is linked here, uh so you can basically find in github as well.

B

It's under dania minus sega, slash atomic cross chain, and this repository basically includes uh all of the codes that I'm that I'm gonna presenting today.

B

So let me start basically with the introduction.

A

So what problem.

B

What why do we need? Why do we need such such tasks? Why do we need like this, this magical things like like hashtag contracts and and then only cross chain swaps, so the problem is, is basically the usual problem as as as the problem for blockchain, uh we want to have something as a value exchange without trusted intermediary.

B

uh Of course, there's one possibility, uh that's the blockchain for that, so we can have like, like a value exchange uh in one chain, without trusted intermediary uh with the help of a peer-to-peer network, but we would like to focus a little bit here on something as a cross-chain interability interoperability.

B

So supposing we want to somehow exchange values uh that are basically somehow manifested on on two different chains, two different blockchains? Then we will have a problem, and so I have this picture here. At the end, uh it might look funny uh so basically what we want to do. We have like several blockchains or several systems.

B

It might even be actually centralized as well and we want to do kind of a transactions on on these systems, but in a way that either all transactions are executed or none of them executed. So that's that's. What we want to do somehow uh might be a funny thing. This is kind of an opposite of a mexican standoff. uh So in our case I mean if all all transactions are executed.

B

We are happy if none of the transactions are actions executed. uh We are not so happy if if some of the transactions are executed and the other parts are not, then we are absolutely not happy. uh So that's our value exchange. Actually a mexican standoff is the opposite. So if you know I mean every every transaction is executed, then then none of the participants are happy. uh If some of them executed, then some not then perhaps one or two actors are happy.

B

So it's just you know it's a little bit like off-chain introduction to the to the topic.

B

So again, um so the problem is, we want to do value, exchange, uh value, transfer and vital trans trusted intermediary and it works pretty well. If we have one chain so like we have ethereum, uh we can do value exchange uh for each, for instance, or for esc initial. uh It works, it works pretty.

B

Well, uh we get blockchain like bitcoin, so we can do like like value exchange, value transfer in the bitcoin blockchain as well, and of course you get like other ledgers as well like like consortium ledgers like like hydrology, so we can do kind of a value transfer uh without trusting intermediary, and this is actually not so much exactly right with hyperledger fabric, uh tripoli,.

A

B

Is rather kind of a semi-trusted network, so I would say we can do kind of a value exchange with a semi-trusted intermediary with high volatile family. But the point is as soon as we want to somehow uh cooperate uh between two different blockchains. uh I mean this whole situation is, is getting more more and more complicated and somehow the idea is we want to.

B

In a way that it's it's, it's not trusted, so basically uh let me have the very simple example. That's the classical example. uh Let me have let me assume uh that there's alice and bob um cryptography, that's usually alissambo, and then what we want to do is that alice and bob wants to want to basically exchange ether for bitcoin.

B

That's the classical example. uh We will see another, I mean if I say he be here bitcoin. We will see some kind of a token on hyperledger fabric later on the demonstration, uh but usually like introducing uh atomic russian swaps or hdlcs start with with the example of ether and bitcoin. So I would just stay with eater and bitcoin for the first round.

B

uh But again, uh if you don't like it, just just imagine that uh instead of bitcoin, uh we will use like kind of a hyperledger fabric uh account and stock and this stuff um in the long run. So what we want to do. We got two chains. uh We want to exchange ether for bitcoin. uh Alice, wants to send some ether to bob and bob wants to send some bitcoin to ether as an exchange.

B

So that's that's. Actually, the problem and the main problem is that these are two chains, so the question is: how can we do these two transactions um in a way that I mean both are executed, of course, or none of them executed, of course, and both alice uh gets the bitcoin and bob gets the eater, or none of them gets that money uh in a way that we are working on two different chains.

B

So one way is a pretty much centralized uh solution. We.

A

Can have something.

B

As a centralized component, so one way of doing is that, like alice sends this eater to this: let's call it as a cast of the rs2, uh it's a centralized component and then boop sends basically bitcoin to this component decentralized component and where these components checks. If both money arrived and if, if they arrive, then basically it sends back so it sends back like bitcoin to alice and it sends ether to bob minus some kind of a v.

B

So that's a possible architecture. However, I mean so having like decentralized protocols. uh People usually don't like this solution, uh because it's pretty much centralized it has some counterparty risk, so it has actually all the problems uh that basically centralized into institutions having.

B

uh So it's not really cool such an idea uh having having in the blockchain space.

B

So what we should do, basically, that we should somehow implement this kind of mechanism in a decentralized way, and basically this should somehow decentralize this exchange this. This is ss2, so it shouldn't be like a centralized party or or a centralized s2.

B

It should be somehow decentralized working working in both both chairs and what should happen, basically that, yes, I mean alice, sends this. This eater not directly to bob, but to this somehow distance, wise escrow service and bob sends the b, the bitcoin not directly to alice, but somehow to these that school service and if both school services or the one decentralized restaurant service gets the money. Actually, then they can do the real transfer so like transferring bitcoin to alice and transferring ether to bob.

B

So that's actually an atomic cross chain swap in a very high level. uh That's the idea uh behind and that's actually a solution for such a value exchange uh having in a in a totally different distance-wise way between two blockchains. So again, just consider that, basically I mean one part. This part is basically on on ether on etl and the other part of the problem is on bitcoin uh or, as we see it later, I mean these. These are just two arbitrary chains.

B

uh The first one can be ethereum, the second one can be hyperledger fabric, or this can be actually any kind of two two block chains uh in in between. We want to do kind of an interoperability uh service, so that's an atomic cross chain swap. So the question is how we build up such an atomic cross chain swap and for that we have to actually introduce uh building blocks and the building block is the hash time lab contract so basically hash time.

B

Contract is a kind of a transaction that we will see in a second uh which helps building up atomic cross chain spots. So hdic is, is not just for fun. The main idea for hci it's kind of a cryptographic protocol which helps building up cross-chain interoperability and atomic cross-chain swaps. So that's the idea for htlc hash time contract.

B

So let me just start and take a look. uh What is exactly an htic a hashtag contract? So if we have like a standard transaction in blockchain, uh the standard transaction is blockchain is, is either executed or not executed.

B

uh It differs a little bit between different blockchains so like if you have like the hyperledger fabric transaction high, pelleted transact fabric transactions are final, so they will be executed uh with the probability of one uh and then basically like bitcoin transactions are probabilistic, so they won't be executed with the probability of one but like with the probability of 99.999 percent. It's usually after six confirmations.

B

uh You can say that basically, it's 99.999 percent uh probability that the transaction is executed and ethereum it's even more complicated uh because uh it used to be like fully probabilistic but there's some final finality settlements, as well as far as time at the moment, uh with like hundred bucks as well.

B

So it's a little more complicated, but nevertheless, uh so we can say that, after a certain confirmations of block, basically a kind of a transaction like a value transfer like if I just just transfer bitcoin from one account to another, one is executed on the blockchain. So it's it's final. I mean in the final, either either either probabilistic final or or or or really final.

B

So that's a classical transaction and what we want to do in uh in an htic. We want to do kind of a transaction that is not fully executed, but only partially executed.

B

So um supposing we want to send like bitcoin or ether to bob, we want to create such a transaction uh that doesn't create actually doesn't send bitcoin or ether to bob, but that sends this bitcoin on ether to kind of a temporal state.

B

So this temporal state that you can see here below is neither related to alice nor nor to bob it's it's just an intermediary state. Somehow, um and then it can happen something with this intermediary state. But, like you know, I mean, if you just send like five bitcoin from alice to bob, but you don't send it directly, but with the half of this intermediary state, then it looks that way that this five bitcoin or five meter will be in a temporal state.

B

So it won't. I mean alice, won't have this five bitcoin anymore, neither bob, but this five bitcoin or five heater will be in a temporary state. Somehow so that's important that this transaction is kind of not final or not even probabilistic final, but first we want to transfer uh this like five bitcoin or five liter to a temporary state to an intermediary state to something which is which is still not final.

B

So that's the first building block and as a second one, we want to have some conditions in this temporal transactions in this temporal state. uh Actually, two conditions, uh one condition would basically uh send this, uh send this money really to bob so from the intermediary state to both and the second transaction would actually revert this transaction.

B

So these are the two conditions uh that we want to somehow build in in this stamp or our transaction, and then the first condition is a hash log. So what we want to do? We want to have basically a secret password.

B

uh We want to create a transaction uh that that has kind of an intermediary state, and then we want to have a password and as soon as this password is activated, we want to make sure that this transaction is fully executed.

A

B

She doesn't send it directly but to an intermediary state where there's a hash lock, which is basically a secret password and as soon as the secret press was revealed, then bob gets the money. uh If this password is not revealed, then basically bob doesn't get the money.

B

um It can be imagined as basically as a lock and if you have the key or the password, then this transaction will be fully executed. If you, if you do not have the key, uh then basically this transaction won't be executed. That's the hash, lock. um The reason is that it's hash log, because it is actually implemented with the help of a cryptographic hash function, so cryptographic has hash function, um not gonna go very much into the details, but basically you have some some paths for some keys.

B

uh This is the cat and then cryptographic hash function creates some some cryptic output with like 32 bytes uh innovated, based on this output. I mean I mean the key or the password can be revealed. uh It can be hacked, but as soon as you have the key or the password, basically, uh this output, this lock can be very easily computed.

B

So that's what we have here. uh Basically, it looks that way uh that we want to have a hash, lock, condition, hash, lock, condition for heavy hash load condition. We will have basically a pre image of a hash function, that's the that's our password and as soon as we know the password. uh Basically, we can fully uh fully have this transaction fully commit uh our transaction.

B

So that's our hash lock. uh So this is the slide for unlocking the unlocking the transaction. Again, we start this sending one bitcoin to an intermediary state where we have basically a hash value of an unknown secret of an unknown block of an unknown password and as soon as somebody reveals in a special way this password this key, then this transaction will be fully executed.

B

So that's the hash, look part of a hash timelock contract and we got basically another part. That's called the timelock.

B

So supposing we have this temporal transaction that can be basically somehow carried out or committed uh with the help of a password which is actually a pre-image of a hash function, we wouldn't like actually to wait forever for unlocking this transaction.

B

So as as you see, or as you can imagine, uh having this intermediary transaction, uh it looks that way that at the moment, neither at least nor bob has basically this like one bitcoin or five bitcoin or five leaders, because it's somehow in an intermediary state, which is not very much practical if it if this money uh remains there forever, because it means that it is lost which is um not so much practical.

B

So what we want to do is to build in a kind of kind of a time lock a kind of a timeout. So we do this transaction to an intermediary state. uh We wait like six blocks or six hours or six minutes. If anybody gets the password, which is the primage of a hash function, then we can fully execute this transaction.

B

But if this time lock uh basically expires, then then we would reward this transaction. So after that we say that hey, if, if nobody uh gets the password, nobody wants to have this transaction fully executed in this time limit, then let me just revert this transaction. Then it's somehow not gonna work, and this is the time.

A

Lock, uh basically,.

A

B

This is what happens uh after a certain time. Lock it doesn't possible, uh it's not possible to to activate the best password anymore. uh You can't you can't have this uh image of the hash anymore. You can't commit the transaction to bob, but what's gonna happen is that there's a river transaction and then the fund from this intermediary state is simply reverted to alice, so alice gets back, basically uh the money.

B

So that's all that's the time lock uh and basically, that's hashtag, lock, contract. Again, it's very simple: uh we don't have one one fully executed transaction on the blockchain like fully executed transaction for transferring a monitor or one bitcoin from alice to bob, but we execute this transaction somehow into an intermediate state and from this intermediary it states. There are just two conditions: how this, uh how this transaction can be either fully executed or reverted, and then you can fully fully execute it.

B

If, if you know the password, if you know the key, uh which is basically the uh the pre-image of your hash value, then book gets the money money and if you don't know- or if you don't want to use for some reasons this uh this lock. This hash log then the after a certain time. uh Timeout this transaction can be reverted, so basically alice gets back the money, uh pretty simple, so that's like htrc, uh and then I'm gonna show some very simple examples.

B

uh How such hdlcs can be implemented in each idiom or or even with hyperledger fabric. It's important to note these are these are not productive, ready solutions. These are more strict for.

A

For them purposes,.

B

So what I'm having here? Basically I just use remix. I hope I hope you can see actually the code it can be deployed basically uh to the mainnet as well. I I use here remix, because it's just you know I mean I mean much much faster uh to demonstrate both the code and actually the transactions, if I just deploy it to to the mainnet like or even drop stand uh I mean for for all transaction. I should wait basically a couple of couple of like uh you know.

B

I mean I mean not minutes, but about 10 seconds at least.

B

So what I'm having here is a very simple hdic implementation.

B

It looks that way, as I mentioned, so we got like alice.

A

Hey daniel sorry to interrupt and alice.

B

Yeah sure sure uh let me have some some some questions, if you, if you feel like uh just I mean some short questions. uh Well, let me just much better. Let me just take a look on the chat yeah. I should so you don't see the code.

B

So you don't see the code at the moment there should be a chat window and some some solidity code.

A

Basically, on my on my be.

A

The presentation is on the screen: okay,.

A

So, let's try to.

A

Let me take a look.

A

So how about now.

A

Perfect now, okay.

B

Yeah, so let me just know, I I think I think it should be uh so if I just change window theoretically, I was.

A

B

I was sharing my desktop, but if I change window it doesn't always work, so it might be the case yeah. So what I'm having here is a very simple hdrc on ethereum. It looks that way. uh I hope. If I play with the window, you still see it so basically from alice. I want to send some heater to bob and this is not a general smart contract, so it's actually used just for this use case just for very simple uh example.

B

So supposing we have ethereum uh and supposing the value transfer in ethereum is sending ether, then the intermediary state can be basically a smart contract. So what I do basically, I don't send directly either from a list to bob, but I will send it to a smart contract. That's basically an htrc and that implements my learning.

B

So this is very simple solidity. uh If I just if we just take look basically, we have like the addresses, so we have like the addresses from alice. uh We have two bob. We have one timeout and one hash lock. uh So basically, this whole hdrc is the smart contract itself. It's nothing special.

B

uh We got one even that's committing actually the even so. If we, if you commit the transaction, there will be an even phrase reason we get the constructor I mean constructor looks that way we initiate the transaction uh from alice, so basically alice always who deploys this. This smart contract and the again. This is a very, very simple example, so it is assumed that for for each hdlc you just deploy a new contract. It can be done in a more complicated way, of course, and more productive, of course, but that's actually the simplest thing.

B

Implementation so basically alice deploys this smart contract, so alice will be the deployer and we get some parameters parameters like bob, the hash clock and the time lock, which is actually a timeout, so nothing special.

B

uh It allows payment. So basically it works that way, I don't send directly ether to bob, but I will send it to this intermediary state. That's my intermediary state, that's a smart contract and what's gonna happen is uh there will be from this.

A

Smart contract to functions uh that we have it actually with green.

B

And with red, so one will be the commit.

B

And the second one will be delivered, so the other one will be delivered.

B

So if you just go back, we see these functions. I have one function which which gets how much balance do I have in my contract, and I have just two two functions. Two transactions. One is the commit. I can commit the transaction uh with one input, that's the secret hash, that's the that's the primage of the hash, or we can say it as a password of basically this hash and then I'm checking is the password is good. uh So I mean, if I initiate this contract, I will have the hash log.

B

So if I have the password, I should take a look that this special password is really the premier of this.

B

That's important, I take a look if time lock is not activated not already activated, so if timeout is still not happened, then I'm pretty happy with that uh and if everything's set, I just transfer basically this money to bob. uh So this is like the this is like the commit part. Basically and what's important or it's gonna be important in the future.

B

I just raised basically one event uh which contains this: this secret uh secret password basically and the second one is revert. I just use c reverting because reward is, uh is, uh is a keyboard in solidity, so I can't have it as uh with the name as reward. So it's just reverting uh it's very simple. Basically, I take a look if, if time lock is active, uh so it's I mean if the would already happened and- and if so then I rewrite this transaction, which means that I just I just send that demand to alice.

B

uh It's pretty simple. uh Let me just uh let me just show how it works. uh I just compiled it. I hope it works, so I just use basically this this remix stuff. I hope it's.

A

uh It's spectacular enough, uh not quite sure if I have my transactions somewhere yeah here is my transaction window.

B

So what I'm doing? Basically, I just set up here the the basic series, so I have like one one deep I mean. Let me have let me just change this. uh Let me have just two accounts.

B

This one will be deployer.

B

This was the third one uh and then the deployer will be alice and then the fourth account this was the. This was the fourth account and the fifth second is gonna, be bob.

B

So this is the fifth second. So what I'm gonna do? I'm gonna initialize this contract as alice? uh This is the account for alice and, if I have want to deploy, I should use three parameters.

B

I should use basically the the address of bob. I should use the hash log and I should use the timeout as well, so I'm gonna have this address to bob.

A

A

Generate bomb password.

B

So let me have this uh hdrc. That will be our password at the moment. So what I'm using here is the hash function of our for secret. So that's our secret or that's our password and I'm just using the the hash function.

A

For that and then it looks that way, this is my second parameter, so I should use like 0x and I.

B

Want to use the timeout uh time of this, I mean pretty much in a simple way: it's like unix timestamp, so I will use kind of uh 2050.

A

For instance- or I don't know 30., uh so I just want to make sure that it's it's.

B

Not expired, it's just for demonstration for for normal use cases you can set this like you know I mean for the next hour or 10 minutes or 15 minutes or something similar. So that's my time mode.

A

B

A

B

So basically I mean let me just transact again because it was already deployed. So let's just have it again, so my contract is deployed and it looks that way. Just try to zoom a little bit in. So I'm not quite sure if you familiar with remix, but on the left side we can actually take a look on the smart contract, so we can take a look like the transactions and and some of the parameters that you can reload. So we can read out that from alice address. Is this one.

B

Is this one? The smart contract doesn't have money at the moment, uh our hash lock, that's the hash. Is this one, and our timeout is something this is. I don't know uh if I'm not mistaken, that should be like 2030..

B

So it's a pretty. I mean you know it's a pretty long time. So what I'm gonna do is it's pretty simple. I send some some heater to this contract and I do it in a way I just send like 10 eater to this contract and I'm having this. uh This is elise, so you can check that it's having like 99 eater on these 10 accounts and I'm sending like 10 liter to this smart contract.

A

Let me transact so at the moment.

B

We got an eater which is in this intermediary state, so it's it's neither neither on the account of at least nor, from the account of bob it's somehow the smart contract that can be sold as an intermediary state.

B

So I got here two ways of of somehow resolving this intermediary state and then, of course, the one way is like committing this transaction. If I want to commit the transaction, what I have to do is to sign this password is to have this password. That was htic.

B

So supposing I just want to commit this transaction, I have to basically sign- or have this password, this primage hash, primage and then say commit and if we say commit, then theoretically, bob that is the next account should get. Basically, this meter.

A

So, let's take a look if it works.

B

So the transaction has been executed. It looks great uh if I take a look: get balances zero. So basically the the ether has been transferred uh from the smart contract from the intermediary save state, and if I take a look here, you can see that bob, which was the following account, has something as okay I mean revert is pretty much the same. uh I should make sure that I have some some values, that is it somehow in the in the near future and then wait a little bit and we can revert the transaction as well.

B

So this is basically an implementation in etlu.

A

B

The private scheme I mean the private key- I mean the smart contract doesn't have private keys. uh Smart contract in ethereum can actually send send eater, uh as it is programmed uh smart contracts. I mean. Even the address of the smart contract is created with the help of the creator account, so spark contracts do not basically have uh have private keys. uh Ethereum works that way that you got externally on the account and smart contracts externally on the accounts.

B

Having private keys can interact with the network can interact with smart contracts, but smart contracts themselves do not has private keys so anyway, um let me take a look: how such a thing look like with hyperledger family and uh so first question. If you see my screen, I just changed to visual studio. I I hope, actually uh I mean desktop, sharing followed my visual studio code. So let me know if you, if you don't see, okay, awesome.

A

So if you don't see, I believe your code.

B

So, first problem in high pleasure fabric: you don't get something as token or eater or crypto or anything. So what I'm doing is that I implement something similar. So what I do basically I I have some some tokens. Tokens are very easy. uh I will have some basic token functions.

B

It's like mint token minting token is nothing special if you're familiar with with hyperledger fabric, I just use, I just put into blockchain an account which is an id that will be alice and bob and basically a balance. So that's all it will be very simple use case. So if I mean token, it means that I basically put something into a blockchain.

A

So this function is.

B

With an id and with an amount- and what I do is that I put this amount uh into this id so basically, I will have like, like basic ids in hyperledger fabric, and for this basic ids there will be a kind of a kind of an amount associated, and this is a very simple like token use case in high collagen fabric. um You can have it in a more complicated way, but it's again it's just for demonstration.

B

So first I had to create actually some some primitive functions. So we got like get balance. uh Get balance. Looks that way that we get actually the id that will be alice and bob, and then what's happening is that I just get the balance. So I really read out the value uh what's in this id and then it's a number. So if it's hundred I got hundred tokens if it's hundred and fifty I got 150 tokens.

A

That door, that's.

B

I have something token, then mint token actually adds some some money to the to the token: it's not money. It's you know it's just effective money or effective token. So I just read out the amount. That's on the uh that's, basically on the uh on the given account and then I just I just add some some more money uh for that. So, if like, if I'm into token foreign, then alice previously having like 100 tokens, if I mean like 100 more, then she will have 200 tokens pretty simple.

B

I do have some burnt tokens as well. It's the opposite of me, so I decrease the the amount of money for alice and what I'm having for the first run. I get a transfer and transfer is a final transaction. It's a final value value transfer. Let me put it that way. So it's very simple. I just burn some tokens from the from account and I mean some token to the two account.

A

Error handling uh slight catalyst to just version.

B

So basically transfer looks that way I got from. I got two and I get an amount and then, if at least having like 100 coin and or token book, having like like 100 coins as well, if I just transfer like 50, then one will having like like 50 and the other one is like 150..

B

So this is a transfer, uh and this is a this is a this- is a very classical transfer setup transfer in ethereum. Again I mean hyperledger fabric. Do not have this basic structure for tokens, so I had to implement something to work with. uh You can do it in a more complicated way as well. There are, there are examples, uh even for hypoallergenic fabric, where you can use different token standards. Even so, what I have to do is to extend this very.

A

Basic transfer function.

B

In a way that it works with in in an hdr cv in in a hash time or contract way, and for that I will have something as as transfer conditioner and transfer. Conditioner is a conditioner transfer which is pretty similar to ethereum, so I'm having for the first one id, which is which basically lock id um it's strangely set in the in ledger.

B

It's perhaps not so important, but what I'm having is a from id is a two id similarly to to the transfer or to ethereum, and I have the amount amount is pretty simple as well, and what I'm having is two more parameters.

B

I got the hash look and I get a time lock as well, so transfer conditioner is more complicated. Basically, it's it.

A

Makes I mean it burns from from one.

B

Account but it doesn't add tokens to another account, but it somehow uh puts these tokens to a temporal state which looks that way that I just create a hash timelock, which is again a structure that I that I put into the blockchain to the hyperledger fabric blockchain and that's transfer conditioner.

B

And similarly, as seen as in ethereum, I will have I mean I have one function. I can read out this hash timelock, but basically I have two functions. One is commit and commit works that way that basically I have to refer to this hashtag contract that I created. But basically what I have here is the pre-image.

B

So the primage of my of my of my hash that I created in the conditional transfer and if this primage is cool, then basically the party gets the money, so the so the transaction committed fully.

B

So basically, there will be the other part which was missing in the conditional uh transfer and that's minting the money and there's another way, which is reward. Sorry word is again similar. I just use this lock. This hashtag, lock id but basically revert, looks that way uh that if basically uh this timestamp is already in the past, uh so the timelock has been activated then basically bob gets the money back. uh Basically, so bob gets the tokens minted.

B

A

Me just start and let's just take a look: if.

B

It works uh uh again, I'm not quite sure if you're familiar with hyperledger fabric, but this is usually not so spectacular. So what I'm having here.

A

A

A

And let me just show what I'm having here. I just.

B

Prepared the very simple presentation here, so it's a very simple network. I don't want to go very much into the details. I just use it uh to to start basically everything so what I'm having here uh in the middle in the meantime, it starts what I'm having here. I just basically what I want to do here.

A

Let me just go back to my sketchpad. uh I just.

B

Want from bob to send some money to eat to alice, so that's our use case uh in a second uh hashtag contract. So I want to send some some high pillager freddie token from bob to alice, and then this gets to an intermediate state and then basically, if I commit, then this transaction will be fully executed and if I revert then bob gets actually these hyperledger fabric tokens back.

A

So something is not right, so I hope it will work eventually just a second. This is the classical demo effect.

A

B

So what's gonna happen here, uh I will have some comments, uh which demonstrates that kind of stuff. First, I will just get the balances of alice and bob. uh Basically again, it's a very simple command. It's get balanced and I have just the id it's bob, so basically that's the icon. For bob. I have the ids elise, that's the that's the account for alice uh and the first ibm means some token.

B

So I will meet like 100 tokens for alice and I will meet like 200 tokens for bob at the moment, after minting tokens, I just again get the balances again for bob and alice uh and then, after that I just create a classical transfer. So classical transfer looks that way. uh I just want to send some some some high pillager fabric tokens from bob to alice. It's just 50 token.

B

So after this step, basically bob and that is- should get like 150 150 tokens and after this step I will execute a conditional transfer and conditional transfer looks that way that ib is sent from bob to alice 50 tokens, but in a conditional way. uh That means that I'm having, on the one hand, basically uh a hash of a pre-image password.

B

This is actually not exactly the same hash. It's it's the hash of password, if I'm not mistaken and I'm having basically a time value as well. This is zero normal time at the moment, so, basically, uh this temporary transaction, this conditional transfer, can be executed with the help of the of the pre-image of the hash and up to up to 2022, basically uh so that so on and after having this uh stuff first, I should get basically a time lock, which is a complex structure.

A

Written in the written in the.

B

In the blockchain- and I would expect something that bob getting like uh 50 50 tokens less but alice didn't get this 50 token, uh so this 50 token in a temporary state, and after that I will commit basically this uh explicitly this uh this this transfer, this hdlc. So what I would expect that actually alice gets this 50 token that was in a conditional state previously.

B

So let me take a look if it works, and then it looks much better.

A

B

See I can show these steps basically up and running as well, so the first step is bob, and that is both are having like zero tokens.

B

So the first step is that I mean like 120 tokens or 100 and 200 tokens for alice and bob. So basically, after this alice sorry bob having 200 tokens, and that is having 100 tokens after that, I just make a classical transfer uh where bob transfers 50 token to alice so getting the balance, basically both bob and that is having like 150 tokens.

B

So after that I just do a conditional transfer, which is basically the htrc. That's the hash timer contract, with two conditions uh with the hash and with the time lock and both and.

A

B

But conditionally, so it means that first there will be a time lock, hash time, lock, that's registered in the hyperledger fabric, blockchain and after that it looks that way that the account from bob was decreased by 50. But basically this money didn't arrive to alice, so it's in a in a temporal state in an hdlc contract.

B

So what's gonna happen as the last step. I just commit this step uh here. Actually, the the secret was password itself, and that was that was the hash that I that I that I gave in uh I do not have revert at the moment, but I mean uh it's in the code, so you can, you can make a loop. You can take a look so basically like like executing this. Commit uh what's gonna happen. Is that bob having hundreds but alice having like 200 tokens? So basically the plus 50 tokens uh right.

A

The echo calculus.

B

That's the simply hdlc implementation are basically on high volatile fabric. um I would stop here perhaps for a little bit.

A

If you have some questions, uh some short questions uh and then and then I would just.

B

Continue with one more, it's gonna be like 15, more minutes, probably how you can build up like atomic cross chain swaps between like these two uh hashtag contracts,.

A

Yeah uh david, so uh how it is different from the centralized way like previously, you were saying uh we have one ethereum and bitcoin blockchain network so and there's a one third party e. So that's uh we are sending ethereum to e and again is sending some ethereum converting with ethereum to uh bitcoin, not converting like he's taking ethereum and if they're having some bitcoin again, he is sending that become that value of bitcoin to the bitcoin network.

A

B

A

We are going to see here we are doing the same. We are having one converter. We are sending some transactions from ethereum to that converter and again that can what are sending the transaction fabric so how it is different from the previous.

B

So uh uh I will answer in the in the next next session. This question so based on the two two hdlcs: uh we can build up an atomic cross chain swap, and that will be that will be non-custodial, so it will. It will work without uh without the central party without a.

A

Central trusted party- okay, yeah got it thanks.

B

So hts is basically the building blocks. It's it's like you know. I mean the cryptographic building blocks of of doing something. It's like you need. You need a cryptographic. Hash functions function for a lot of things, uh but it says that's just like a cryptographic primitive. So in this sense, htsc is basically a kind of an algorithmic protocol, cryptographic primitive uh that can be used to build up.

A

B

A

Things, no I'm I was just asking it is centralized or the you know, distributed that new way. That's a hltc, it's centralized or it's.

B

Distributed so I mean htic is just kind of a concept running on a blockchain. uh It's still not it's decentralized, because it's it's on a blockchain. Basically, um but ideas show the protocol in a second, basically and and and you can see uh how it works uh without the central uh without the central uh uh counterparty.

A

Okay, good yeah, so thank.

B

You then, let's cover basically this protocol, because I mean, uh as I see uh we got, we got already the questions related this one. So what we want to do. We want to build up this atomic cross chain swap uh with the head of hdlcs, and this is how the protocol looks like it has. Four steps so first alice creates, creates basically a secret password and then what she does. She creates a hash of this password, uh which is actually the lock itself.

B

So password is like the key and then the hash of the password is is like a lock, and she sends this information. I mean the hash itself and the and the time log to bob. uh So basically I mean she sends the the hash of the password and they somehow agree in a time lock as well.

B

A

Let me just perhaps show it on the screen.

B

What we want to do is that we got here eta, etdu.

A

And we have here hyperledgery.

B

And what we want to do this is alice, and this is bob, and here this is bob, and this is alice, and what we want to do is that alice wants to send some eater to bob and bob wants to some send some some some high pillager fabric tokens to alice on hyperledger fabric, and we want to somehow reach or achieve that these two transactions either happening.

B

I mean either both happens or or none of them happen, so that that's what we want to do, and the first step is that alice actually finds out somehow a password and the hash of this password.

B

And what she sends and- and it's actually a time lock as well, so what she sends for for bob is this the hash of the password?

B

So again, it's important here that actually alice is alice knows the password. So she knows here the password, but bob doesn't know the password, but she sends actually the hash of the password and basically the time log form. So that's the first step. The second step, both alice and bob, creates an hdlc uh with the parameters.

B

So htrc requires the hash, lock and basically the time mode. So what they doing is the next step they both creating uh this, this hdlc so money transfers to an intermediate state with like two conditions. Again, one is the hash of this password and the and the second one is the dialogue and book does the same one, uh sorry, but with but with hyperledger fabric, so what he does he creates this intermediary state, uh but with like two parameters, one is the hash of this password and the second one is d.

B

Is the time mode itself? So that's the second step and the fourth step uh it looks that way that you know. I mean whoever knows the password uh can execute the function. uh So that's what happens. Let me just just uh change to green, so in this example, basically alice initiated the whole atomic cross chain, swap so she knows the password. So what he, what she can do is that she sees that there's basically.

B

Already, an htic that can be executed with the help of the book doesn't know the itself. uh Only alice knows it. So what else can she can basically execute this transaction with the help of the of this password?

B

Okay? So that's that's what she does uh that's next step. Okay, but basically it looks that way. uh It has to be implemented in a way that, as soon alice uh basically commits this commits this transaction. uh This with the password, the password itself is revealed. Okay, so if we can take a look both in the both in both implementations, so basically I mean I mean in ethereum. Everything is basically public. So if you, if you have a transaction with the secret hash, it will be revealed um in a better implementation.

B

I even have basically an event that publishes this password basically same is in hyperledger fabric, it's just a little bit more complicated, but anyway, uh if I just commit the transaction, what I'm gonna do is that I commit the password in an event, so I just publish this password in an even so this this password can be seen.

B

I will discuss the problems of that, but anyway, uh in the normal way, this will be seen. Basically, so what's going to happen, is that alice knows the password? She goes to hyperledger fabric commits this transaction uh with the password. So basically it means that box will know the password as well because he sees the password so, but what bob can do uh he can go to ethereum, there's here, basically an htic which that was created like with two parameters.

B

One is the time mode and the second one is the hash of the best board. So what he can do, he can basically activates and commits this transaction as well, so he will get the e-turn uh and that's what we expect. Basically, at the end of the happy case, let me say that this is the happy case. Alice uh committed the transaction in hyperledger fabric, so she gets the hyperledger fabric token. The pub the password is revealed so with the half of the password. Bob basically commits the transaction on ethereum.

B

So basically, at the end of the day, both transactions are committed on both ledgers. Okay. So that's the happy case. uh We got the set set case as well, so.

A

What happens if you know, I mean at least.

B

At least she she doesn't want to to to to have this transaction for some reasons, uh so she doesn't commit this kind. This part of the transaction then what's happening is that basically, the time lock expires and as soon as the time lock expires, basically the this hdlc. This time the contract is reverted, so the same is going to happen in ethereum. uh If the the action is not activated it's, if it's not committed, then the time lock will be expired and basically uh the transaction will be reverted. So that's what we wanted to achieve.

B

uh It's a protocol that makes sure that either both transactions are executed on both chains or none of these none of these transactions are executed in none of these chains, so both are regarded. So that's an atomic cross.

A

Chain swap and then.

B

uh Pictures but I think uh what I'm having here was perhaps a little bit more visualized. So basically, this is what happens uh both parties doing an hdlc, which is this decentralized stone in a way uh and then basically alice knows the password. So she can actually activate the hdlc that was initiated by bob on another chain uh and then, as bob sees the password, he can basically execute fully the the the transaction on ethereum uh and then it means both transactions will be executed.

B

uh That's the happy case, and the unhappy case is that, for some reasons I mean I mean the hts are created, but for some reasons they are not fully committed because I don't know at least goes offline. So you can imagine like here that l.

A

Is cool so fine for any.

B

Sense so she doesn't activate the password on hyperledger fabric uh and then for some reasons, it's just not activated, so it means that basically the timelock will be expired and then all the funding gonna go back basically uh to the to the original initiator.

B

So that's the atomic cross chain swap uh between between two uh two ledgers. uh With the help of the uh with the help of the code that I shown you can actually make it I mean I can do it uh very fast if you feel like, but perhaps I would just have some practical considerations uh before before showing the demo.

B

So this is the theoretical way of of doing like uh atomic cross chain swaps, uh between hyperledger uh fabric and and ethereum, or between any any two blockchains. It's important to note that it's not so.

A

Straight for more.

B

If you delete between and high pressure fabric, there are some tricks actually that you should be aware, um and then there are some general tricks that are not related to fabric so like usually it's not the best idea to to implement it on your own, uh such an hdlc, unless, unless you do not have any other chance, so basically there's like uh like erc standards for that uh that are pretty much a little bit like work in progress but like for ethereum there's an erc stand.

B

That's that's the erc 1630 uh there's no such thing for for for hyperledger fabric. As far as I know, so that's one thing: if there's already something implemented, it's just better to use it, the other one. It's it's important to know that I mean this algorith work works pretty well. If you transfer tokens because I mean there's, there's an assumption and it's a that's- an economical assumption that both party want to get the token. So it's it's better.

B

If, if I have eater than if I don't have the eater, it's better, if I have the bitcoin, then then, if I don't have bitcoin it's better, if I have the the hyperledger fabric token than if I don't have this psychological token, but it's important to know that's an economical consideration, so it's it's. It's usually valid for for such tokenization stuff, but it's not necessarily valid for any transaction so like, even if we have token uh just imagine that the token is is not money.

B

It is not ether or bitcoin or or something positive, but like getting. The token is something negative so like if like getting a token uh that is, like you know, it's like a penalty for a for a driving uh or a driving license penalty point or something then it might not work so well, because I'm not really interested of of getting an additional penalty point for my driving license.

B

So I have here like opposite, economical interest than than getting eater or getting bitcoin or getting something positive uh token in hyperledger family. So that's important uh it. It must.

A

B

That this is a crypto economic protocol and it has some economic consideration as well, and the economical assumption as well is that I mean getting this eater or token or fabric token is something better. So it's it's better if I have it than if I don't have it. Basically, that's the second one and the third one uh is basically so.

B

The point is that hyperledger fabric is a console, assume blockchain, which means it's permissioned, so hts's and atomic cross chain swaps work pretty well if you have like public blockchains, but it might be tricky if you have consortiums consortium blockchains- and the point is that, if you have permission ledgers, I mean the system might be tricked a little bit. So, for instance, you have to make sure that if this password is activated here, then then bob needs to needs to have needs to have the right to read it.

B

So as it is a permission ledger, there might be some attack that you know. I mean at least um how makes sure that bob doesn't have access anymore to hyperledger fabric. She just uh activates this transaction with the with the password bob, doesn't see this the password anymore, uh so he he can't really actually execute the the the transaction on ethereum. So it's not always happens. It depends when you start this transaction, but there might be tricky uh if you have one ledger as the cause of assume one.

B

If you have both ledgers as consortium ledgers, it's even more tricky, so it has to make sure make sure that the the parties I mean the right of of reading out informations for the parties are not revoked in the mean in the middle of the protocol, and but last but not least, there can be some uh some timing issues between the different uh blockchains as well. That must be implemented carefully.

B

So this is the basic idea. So I would stop here and then I would just try to have uh answer the questions uh again. This is the basic idea here.

A

So uh is there any specific values there like if uh ali is sending a hundred eighth here to bob, so how much uh apple is a fabric token bob needs to again send to alice. So is there any link between them or like for some amount of ethereum? How much amount of apples and fabric token needs to be needs to be shared.

B

So I mean I mean regarding the value it can be somehow negotiated. So, like you know, I mean it's. This is like 100 liter.

B

And on the hyperledger fabric, it's, like I, don't know two tokens.

A

Who will define that? Where, should you find it who will defend it? It.

B

Will be, it will be divided by the participants. So, as you basically, I mean as alice initiates. Basically the this whole protocol, but you know I mean bob has to agree uh so they they have to agree in the in the in the hash of the password and in the timelock as well, and they must agree uh at the beginning uh in the exact value exchange as well. So so they must agree that that okay, one transaction, will look like in one chain that I have I have.

B

I have hundred eater and the second one will look like that. Okay, I have two two tokens, so they they must agree at the beginning uh uh as they as they exchange these two parameters. What's the what's the exact value value exchange?

B

That's one way. Actually, uh as far as I know there, there might be some some protocols as well uh that try to try to integrate uh hdlc with with like uh with like decentralized exchanges and in in that sense there might be. But it's you know it's way more complicated, but this uh valuation might might not negotiated by alice and bob, but might come from from uh from a decent rise exchange.

B

Somehow and then they only have to agree uh it's possible, but you know it's not part of the the atomic cross chain swap uh atomic russian swap itself a protocol that can be integrated. So if you have like a decentralized exchange that makes some kind of an order book matching, for instance, and based on the order book, matching uh saying that that the current valuation of of two token is hundred each or uh and it's it's okay for both parties. Then this valuation might come from a decentralized exchange. For instance,.

A

B

Again, it's like a.

A

Little bit more complicated using schedule is it? Is this used? Yes, it's applicable for supply chain. We can implement in supply chain.

B

So so supply chain is tricky uh and the problem is with supply chain. um So so so, as you see, I mean I mean what you see here basically, is that these these assets exist fully on the blockchain and then as they as they exit fully on the blockchain.

B

This is simple, because you can have this this intermediate state.

B

If you have, if your supply chain, you can have some more consideration, because I mean, if you have supply chain, then usually your two tokens is is something tangible. So it's like two physical containers.

B

Okay, so you want to do kind of an exchange that two weeks two two physical containers are exchanged for like hundred liter, uh so you can model this intermediate state, uh of course, in the blockchain in hyperledger fabric. But of course the question is: what's gonna happen with these physical containers, so I mean, if you have supply chain uh the trick. uh What must be cost uh is that you got some physical goods, and then I mean perhaps you have this intermediate state in the blockchain.

B

But it's the question is: if the, if the, if, if this intermediate state can really be interpreted in the physical world as well, so like you know, I mean you got two containers, so how you put two continents into an intermediate state. um It's.

A

Probably not not the most trivial question yeah, I got it. You gotcha thanks thanks daniel. uh So let me take a look on the questions.

A

When the time is finished for the uh for that.

B

A

Be called by the person.

B

Let's just imagine this situation that this password is not activated, so something went wrong. This password is not here so what's gonna happen is that that we have here basically uh this this this intel. I mean this like hundred detour, which is in an intermediate state.

B

So actually anybody can call this contract, so anybody calls this contract with a reward function at least gets back the money. So it might happen that we have some some centralized stuff working or calling this function, but it's not necessary so alice, it's her. It's her own interest, calling this function and reverting the money, because I mean if, if she rewards she gets the money back very simple, but actually I mean anybody can can call it but usually alice who caused it because she wants to get the money back.

B

And similarly, here I mean we get some high pressure fabric transaction, uh some in an intermediate state, some tokens, um so supposing it has value, uh then, of course bob wants to get this value back and then bob gets this value back if he calls this reward function, so he will revert this. He will call this revert function, but again it's not necessary. So, theoretically anybody can call this reward function, but you know I mean it is supposed that those who will profit from it.

A

A

I can't call it immediately.

B

She has to have access.

A

B

A

B

So so that's right, that's correct! So again! uh Basically uh so so that's that's one of the that's one of the things uh thing that that want to be. That must be actually um that one that must be uh considered if you have like hyperledger fabric network. So one one thing is basically uh it's a permission ledger.

B

So we got like read, access and write access and then so one problem can be if like uh alice, alice, really is the password here uh commits this transaction and then, basically, before committing this transaction, she just drops out books somehow from hyperledger fabric. uh That's the problem. uh The other problem might be if the transaction should be reverted, but before reverting the transaction. Somehow, in the meantime, uh bob bob access will be will be denied from the network, so yeah um the algorithm works.

B

Well, if, if basically uh I mean the excess rights of alice and bob will not change in the middle of in the middle of the protocol, uh that's uh that's what's tricky and then yeah. We can say that I mean if, if we have hyperledger fabric, it's it's not a totally trustless solution. It's just because hyperledger fabric is is not totally trustless.

B

So it's like a semi-trusted network. So if we integrate, like you know a totally trustless public blockchain, which is which is semi-trusted blockchain, um then then for the first up for the naive implementation.

B

What we get is not a totally trustless, but it's kind of a semi-trusted atomic cross-chain swap uh that assumes that, in the middle of the protocol the excess right of the parties in hyperledger fabric will not change.

A

Daniel to protect against this attack is it? Is it an id that you play with who which of the two parties starts the transaction meaning? Is there an importance to either start on the on the semi uh permissible blockchain rather than on ethereum or the other way around.

B

That's a good point.

A

So so you can, you can protect.

B

So if you, if you start from hyperledger fabric, uh then then you protect you protect against one. You protect against one attack, because if you start in hyperledger fabric, then basically bob bob finds out basically the the password uh the hash of the password and the time, and he sends it to alice. So it means that the first step of revealing the password happens on ethereum.

B

So it means ethereum is always public. So so it protects again this uh this kind of attack uh against revoking the the lead right of a party in the middle of.

A

The in the middle of the transaction.

B

uh In the middle of the protocol, uh I'm not quite sure if it if it protects against the other part of other attack as well. So it's like if, if like bob, wants to revoke the transaction, but before after creating this htsc, but before before, revoking before having the possibility of removing the transaction. If his axis is revoked, I mean if he can't contact this anymore to hyperledger fabric. It can still be a problem.

A

Okay, thank you.

B

But but you're an absolute guide, so if you start from another direction, uh then then then revealing the password happens on the ethereum and and you can't block uh basically ethereum, uh so any anything happens on the ethereum is public, so it will be seen yep.

A

Yes, exactly that's fine! Thank you.

A

So let me see the chats, I'm not quite sure where we start but so question. If it is any of the importance which is where it starts.

B

Yes, so that was the question that I that I was investigating a little bit so normally in.

A

B

In an atomic austrian swap between two public blockchain, uh there's there's no importance uh who starts first. If you have one uh one uh consortium ledger, uh then then it's usually better to start on the consortium ledger, because then your password is revealed on a public blockchain.

A

Which, which can't be you know, I mean.

A

B

So which hts in its shorter timeline, the one created by bob in this case, since it's not the best one, so the uh the one that executes first, I think that should be the uh that must be the the the shorter timeout. uh I should think.

A

It over uh at the moment I just uh I.

B

Don't have right, ready answer it, it can be just a problem or that it should be taken care that you got like two block chains, so the time is is is never the same on the on the on the same blockchain. So even if the, if the timelock is agreed, uh then it might be a couple of seconds delay between the two that can be hacked actually uh in some cases, and I should think it over.

B

uh But if you have the the the right order, then there's no uh such uh hacking possibility uh exploiting the the delay of the time. uh The delay of the times uh can object to see. Feliz actually sent an eater.

A

Or could she send less than finds finds out later.

B

Yes, so so the basic, basically, they can check everything uh so on the ethereum. Everything is is public, uh so if you just go to remix, uh if we start such a contract, this contract is visible for everybody.

A

So it looks like they.

B

Can I mean even the code itself can be seen and uh usually uh you know reviewed, but it can be seen that you know I mean it's from alice, it's to bob. uh So basically the addresses can be checked. The balance can be checked, it's zero at the moment.

B

But if it's like five meter, then it's five meters, if it's standing or it's ten meter and so on uh so again it's more sticky on the hyperledger fabric, hyperledger fabric assumes uh for for such a use cases that, if you want to review basically uh your code, then then it must. I mean you have to have the access uh for your for your hyperactive fabric network. uh If it is revoken, uh I mean if your access is denied in the middle, that that might be a problem.

A

B

Yeah sure I mean I mean the video will be available and then basically everything will be available, uh my code and then my slideshow and everything will be publicly available. uh You will find it both in both in youtube. I will link it just just under the youtube presentation and I will link everything in in meetup in meetup.

A

B

Without radiation.

A

uh We, which contract.

B

A

B

So you mean that likely so, like the the contract execution of hyper flagellar fabric, uh it's much faster than an ethereum, I mean the processing time of of a hyperledger fabric. Transaction is like uh three to three to six seconds. I mean the it's like more complicated a little bit uh than like. uh Then like uh ethereum, I mean the whole. The whole constants algorithm is more complicated, uh but it's much faster than ethereum, uh but I guess you mean something if the transactions can be front running front front.

A

And then yeah it's a good question. I mean if there's a front-running.

B

Attack for the whole system, then, then probably you can do it for the first run against ethereum, I'm not quite sure.

A

If there's attack in front running, but there.

B

Might be, but I don't think it's very critical because uh yeah so so what happens? If you see the transaction before before getting to the to the network, uh so you can't double spend uh you can't do anything before so you come through before your time lock expires.

B

It can be an issue if you, if you put your transaction to a network.

A

Very fast before before.

B

The time lock expires and there's there's this kind of a front-running attack, I'm not quite sure, I'm sure so so there might be some kind of an attack, but again so so hyperledger fabric is faster than ethereum. It's like three to five seconds of processing time, and it's just not so easy to see the transaction than in interview.

A

Can this solution be automated without external interaction like.

B

An si server or.

A

Something in the middle.

A

I'm not sure if I, if I understood correctly but.

B

So so there might be the possibility to to have here centralized components generally uh but again, so the point of the other is that it can work in a fully decentralized way as well are, if you want to some put some something through i7 in the middle uh and then start the transactions from a centralized server.

B

Sure it's possible. uh It's again, it's just uh so that's the main. The main idea of the of the whole protocol.

A

So I don't know if I have any more questions or basically.

B

I'm not quite sure if I have the youtube link, that's the youtube link.

A

So just give me one minute and I will try to start the youtube version and perhaps we're gonna have some questions and you mean.

B

Idea of the even.

A

So we're gonna have the youtube version and there's no question uh which looks great so.

B

So then do we have any more questions.

B

So, if not, I would say I would like to.

A

Thank you very much for the presentation uh well and for the for the uh for the for the.

B

Audience uh for for hearing my presentation. uh Actually, uh you can find the code and and everything on on on uh I'm gonna post it I didn't, show actually the the exact atomic cross chain swap uh but based on the two uh hashtag contract. I think it's it's it's more or less trivial.

B

I will also uh also put it here so in the readme file, uh how you can play a little bit like uh with like an atomic atomic cross chain swap between the two two examples code and then then you can actually uh take a look.

A

So again, then, if there's no more questions or comments, then thank you. Thank you very much for everybody and then yeah. I don't know just.

A

To read information.

B

A

From the higher level uh fabric contract.

B

So so the point is vtdu uh that you can't really call external you can't you can't call actually external. So we got an ethereum network, that's our smart contract and basically.

A

This smart control can't call out word so this is like the ethereum smart contract.

B

If you want to import information from the outsider, what you have to do is to have an oracle uh and it can be a centralized or decentralized oracle structure. So this is like the outside world. I don't know how to so. This is the word outside of blockchain. This is the this is an oracle structure. It's like, I think, chain link. uh It was like originalized, perhaps a couple of years ago, so oracle is responsible for reading outside data or uh in the world, and then having this information in your blockchain. uh That's for ethereum.

B

It's pretty much the same in hyperledger fabric as well. I mean in hyperledger fabric. You can theoretically call outside the outside your chain codes. So as far as I know, even in the 1.1.3 or 4 version or perhaps 2 version, it was still possible. I'm not quite sure if it's about the two version, but I mean it- was possible uh for a smart contract uh for a chain code in hyperledger fabric to call call outside uh and like call us call an api or a web service or something, but it was.

B

It was very strong, an anti-pattern, and the reason is for that, because if you did such a things- and usually you got like inconsistent data uh which destroyed your your whole consensus, so initium it's not possible to call outside in hyperledger fabric. Theoretically, it's it's, it was possible, uh but it's.

A

Very strongly and an anti-pattern.

B

If you want to integrate like external data into your blockchain, then then you should have.

A

Some oracle, uh algorithm or.

B

Structure or components it can be centralized or or even decentralized as well. So it's not necessarily centralized.

A

You can have like more oracle.

B

Integrating or reading out data from the real world in an independent way, having some consensus here as well and that's what we call a decentralized oracle oracle structure.

A

Or auburn poverty.

A

Thank you very much.

A

So that's how it looks.

B

Like so, then, any any more questions.

B

So if there's no more question, then thank you very much again and then yeah, I don't know, see we'll see you somehow next time. Perhaps I can bring some more interesting presentations in the future.

B