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Title: Trying to get a deeper understanding of atomic swaps Post by: noobWithAComputer on July 16, 2018, 12:43:59 PM Hi together,
I'm an IT-student and writing a thesis about atomic swaps on BTC and BTC-like blockchains. For the thesis I decided to use BTC, LTC, BCH and DCR. These chains have a somehow similar codebase and the same scripting language (I'm not a professional, so there might be differences, but they are not that serious). And they all have a high enough marketcap to be relevant for atomic swaps. So the goal of the thesis is to find hashed timelock contracts (HTLCs) and connect matching HTLCs from different chains to get the atomic swap. Therefore I first searched the web for anything on atomic swaps [1] and analyzed the input script of this transaction [2] to get a basic understanding how atomic swaps work and what they look like. Then I wrote a go program to search for any script longer than simple P2PKH scripts. This gave me a list of many different scripts which I analyzed by hand to only take the HTLC ones. (Besides many multisig scripts, there is not much to find on BTC^^) At this point I found multiple different types of HTLCs as listed below. Afterwards I crawled* BTC again saving all transactions with HTLC scripts, storing the interesting data like tx-id, input value, pubKeyHashes, the secrets and their hashes. I found about one hundret HTLCs on BTC so far. I did the same for LTC and found about 400 HTLCs. As far as I understood, the secrets of HTLCs have to be the same on both chains. So I wrote another go program to match the found HTLCs from BTC and LTC and got around 30 matches. The next steps would then be to crawl BCH and DCR and also match the HTLCs found there. * Crawling in this case means that I start to search the blockchain backwards (to get the newest first, the beginning years are not that interesting in this case^^) until the beginning of 2017. So about 18 months. As stated in [1] the first known atomic swap between BTC and LTC was made on 19th April 2017 (or April 19th 2017 or 19.4.2017 or whatever you like). So there is not much sense in crawling any further. My questions now are the following:
I'm open to any constructive input and hope you have a few answers for me. Thank you in advance. Type 1: sha256 secret, length=97byte Code: 63 if Type 2a: sha256 secret, length=94byte Code: 63 if Type 2b: sha256 secret, length=93byte Code: 63 if Type 3: ripemd160 secret, length=81byte Code: 63 if Type 4a: hash160 secret, length=86byte Code: 63 if Type 4b: hash160 secret, length=82byte Code: 63 if Type 5a: hash160 secret, length=81byte Code: 63 if Type 5b: hash160 secret, length=78byte Code: 63 if Type 6: hash160 secret, length=79byte Code: 63 if Type 7: multiple ripemd160 secrets, length=80 + n*23byte Code: 63 if Type 8: multiple ripemd160 secrets, length=81 + n*23byte Code: 74 depth [1] http://www.cryptovibes.com/crypto-news/charlie-lees-atomic-swap-between-litecoin-and-bitcoin-was-a-success/ [2] https://insight.bitpay.com/tx/0bb5a53a9c7e84e2c45d6a46a7b72afc2feffb8826b9aeb3848699c6fd856480 Title: Re: Trying to get a deeper understanding of atomic swaps Post by: danda on July 19, 2018, 08:36:27 AM Interesting research. Please keep posting your findings. Do you plan to build/release a tool for people to make atomic swaps?
Well you clearly know more about atomic swaps than I do, but I would guess there are so many types because multiple parties have implemented them in isolation and for different blockchains. Title: Re: Trying to get a deeper understanding of atomic swaps Post by: noobWithAComputer on July 19, 2018, 09:53:06 AM When I find the time to translate my work (I'm writing the thesis in german), I will post them here.
As I will start my Diplom thesis in a few months, I won't have the time to implement such a tool. But I hope my findings may help other people to do so. Title: Re: Trying to get a deeper understanding of atomic swaps Post by: HeRetiK on July 19, 2018, 01:01:40 PM Lightning Network uses HTLCs as fundamental building blocks, so maybe this accounts for some of the HTLCs you are seeing that do not correlate to atomic cross-chain swaps? The first known mainnet LN transaction took place some time in late December 2017 [1] so that should be the first time that a LN related HTLC hit the blockchain. However there are currently more than 6000 LN channels open [2] so maybe LN opening / closing transaction don't satisfy your search criteria and thus don't show up in the first place.
[1] https://news.bitcoin.com/first-real-bitcoin-lightning-network-payment-completed-via-bitrefill/ [2] https://lnmainnet.gaben.win/ Title: Re: Trying to get a deeper understanding of atomic swaps Post by: noobWithAComputer on July 20, 2018, 09:41:43 AM Interesting, thank you for these information.
I just checked the HTLCs I found and there was none in Dec 2017. So it seems the LN HTLCs have another structure. I will take a deeper look into this in the next days. Title: Re: Trying to get a deeper understanding of atomic swaps Post by: Kallisteiros on July 21, 2018, 09:21:47 PM
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Type 2a appears to be broken, couldn't figure this one out. It tries to compare hash160(puzzle_hash) == pubkey_hash1, with both values in the same script, which doesn't make sense. Type 2b is the most straightforward. If sha256 of preimage matches the hash and signed by Bob, or timelock is unlocked and signed by Alice, allow to spend the output. Type 3 is equivalent to 2b, except it uses ripemd160 puzzle instead of sha256. Type 4a just swaps the conditions, which doesn't affect anything (except the switch value you put that will decide which branch of OP_IF will be executed). Plus, as in Type 1, it puts constraints on the secret preimage's size. You got the labels here wrong, by the way, <secret_hash 20byte> and <pubkey_hash1 20byte> should be swapped. Type 4b is the same as 4a, minus the size check. Type 5a uses CHECKSEQUENCEVERIFY instead of CHECKLOCKTIMEVERIFY, which is a minor difference. If you're at block 500, and you want to lock the coins until block 530, you can either say "530 CHECKLOCKTIMEVERIFY" or "30 CHECKSEQUENCEVERIFY" (I might have made an off-by-one error here though, check the BIP for the exact usage). Type 5b: the only difference with 5a is timelock value size (instead of 4 byte integer, you can have it in a more compact form with only 1 byte integer, which will give you a lock period of up to 256 blocks). Type 6: is exactly like Type 4b, only it uses a shorthand for pushing the timelock value. You also got the labels backwards here, swap <secret_hash> with <pubkey_hash1>. Type 7 and 8: as you correctly noticed, they use several puzzles at once. Got no idea why. Maybe it has something to do with the puzzle datatype size constraints on the altcoin side of the exchange. Quote
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Title: Re: Trying to get a deeper understanding of atomic swaps Post by: mr_sparkles on July 22, 2018, 04:54:31 PM You might want to look into the privacy angle: i.e. atomic swaps that cannot be linked across chains by anyone other than the parties involved.
This is a good place to start: https://joinmarket.me/blog/blog/the-half-scriptless-swap/ Title: Re: Trying to get a deeper understanding of atomic swaps Post by: noobWithAComputer on July 23, 2018, 07:54:24 PM Thank you all for your thoughts. Especially to Kallisteiros for your long post.
You are right about the swapped parameters in Type 4a/b and 6. @mr_sparkles I will look into it. This might be interesting. Title: Re: Trying to get a deeper understanding of atomic swaps Post by: noobWithAComputer on September 21, 2018, 10:31:49 AM Hi together,
I finished my thesis now and have some results. I put everything I accomplished in a git repo, so everybody can view my results. At the moment there is only the german thesis, but I will try to translate it within the next days. I hope my work is usefull to somebody. Git: https://github.com/noobWithAComputer/detect-atomic-swaps (https://github.com/noobWithAComputer/detect-atomic-swaps) Greetings. Title: Re: Trying to get a deeper understanding of atomic swaps Post by: noobWithAComputer on September 21, 2018, 11:55:41 AM I will start translating it today. Maybe I get it done this weekend. My thesis starts at the very beginning, so I hope even people who are not familiar with atomic swaps can under stand it.
As this is a thesis to a unimportant module in my course of studies, it was not peer reviewed and also not published (besides my personal git repo). I will take a look at the homomorphic hashing stuff, this seems interesting, thanks. Title: Re: Trying to get a deeper understanding of atomic swaps Post by: noobWithAComputer on October 09, 2018, 08:07:07 PM I'm very sorry, that I was not able to translate it within a few days as I planned... And as it seems atm, it will take a few more weeks, as I have a lot on my table right now...
I hope to get it done this year, but I won't make any promises. Sorry :( |