Topic: Sidechain Observer - Bitcoin L2 Projects & current state of development - page 2. (Read 873 times)

I took a deeper look at the Nomic protocol to describe the incentives governing it here. Nomic is currently functional, but the sidechain functionality is limited to 21 BTC before an audit has been concluded. There is also a fork called OraiDex or OraiChain - they seem to be more active with development, but be cautious like with every new project

The whitepaper is here.

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Nomic is to my knowledge the most advanced project which has implemented a dynamic federation. This means: The sidechain is run by a set of validators which also operate a Bitcoin client and vote for every valid peg-in and peg-out. In the case of Nomic, the sidechain is controlled by a proof-of-stake algorithm, i.e. the validators are also probably those with most stake in the utility token. This makes the incentive structure easier than in merged-mined sidechains if we assume that the stakers are interested in their token's value (what Vitalik Buterin called once "altruism-prime"), but of course if this is not the case then the typical potential vulnerabilities of PoS consensus are also present in Nomic.

The Nomic stakers are also signatories of a multisig address called Reserve Wallet on the Bitcoin main chain. They have to pay a collateral which will be slashed if they misbehave. Via Schnorr signatures and MAST trees up to 1000 signatories can be supported in a so called reserve script controlling the coins. This set of signatories is regularly updated, see below.

Nomic signatories have to vote with a 2/3 supermajority for each transaction they carry out. The voting (through the reserve script) occurs in two ways: via a key path using the Musig2 Taproot multisig algorithm containing a "standard" set of signatories, or with a fallback script using a standard multisignature scheme, if one of the signatories in the key path becomes unresponsive.

How does this work in practice?

1. When a Bitcoin user wants to peg-in the coins (i.e. deposit coins on the mainchain to receive sidechainBTC), he transfers the BTC to the Reserve Wallet via a P2TR transaction with an additional OP_RETURN output containing the sidechain address the user wants the sidechain coins to be deposited to, and a timelocked "reclaim" scriptpath for the case the sidechain signatories are unresponsive, then the user can reclaim the funds after a number of blocks (144 are recommended according to the whitepaper).

The sidechain nodes build a deposit proof from the deposit transaction and publish it in the sidechain network. This will later enable the user who deposited Bitcoins create sidechainBTC on the Nomic sidechain.

2. When a sidechain user wants to peg-out, he builds a transaction on the Nomic sidechain burning the sidechainBTC and requesting withdrawal to a Bitcoin address.

3. Periodically, the signatories publish checkpoints on the Bitcoin main chain. This allows to process deposits, pre-process withdrawals and update the signatory set if the set of validators/signatories has changed on Nomic. Checkpoints are made of up to three connected transactions:

- Deposit Collection Transaction: The signatories spend all deposit utxos to a script containing the current sidechain reserve script. This transaction is only carried out if since the last checkpoint deposits have been made.
- Checkpoint Transaction: This transaction is always carried out, even without deposits. It collects the UTXO from the last checkpoint transactions and, if deposits were made, the UTXO from the Deposit Collection Transaction. The coins are spent to the Reserve script, and if withdrawals have been made, then a second UTXO is spent to which will pay out the withdrawals. The main purpose of this transaction is to update the set of signatories (stakers).
- Disbursal Transaction: This transaction pays out pending peg-outs or withdrawals from the second UTXO of the Checkpoint Transaction. It is only carried out if there were withdrawals since the last checkpoint.

In addition an Emergency Disbursal Transaction is signed, which would send the whole reserve to the current sidechainBTC holders. This transaction has a long Locktime. It protects sidechain holders from a "liveness failure", i.e. when the signatories become unresponsive for a long time. At the same time it slashes all collaterals on the sidechain, so the signatories are incentived to always create checkpoints regularly.

As far as I interpret the whitepaper, the Deposit Collection Transaction is still signed by the "old" set of signatories (where the depositors spent to), while from the Checkpoint transaction on, the reserve script contains the "new" set of signatories and these also sign the transaction.

I also interpret that after a deposit, the sidechainBTC will be created only after another checkpoint (more precisely: the Deposit Collection transaction) has occurred, to prevent the depositors to cheat, create sidechainBTC and then spending the coins of the "reclaim" script path (see above).

The peg-out process depends on the behavior of the signatories before the Disbursal Transaction is built. This means that, before voting positively for a withdrawal, the nodes have to check that the withdrawal request corresponds to a legitimate "burn" on the sidechain and that its ancestry is correct (this should of course be validated continuously by the PoS validators).

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At a first glance the scheme looks reasonable. It does not protect 100% from a liveness failure but as long as the PoS incentive process works correctly the sidechain should also work as expected. In the case of a liveness failure the coins will be returned and the signatories/stakers will be punished for that failure. This means that the system depends heavily on the Nomic tokens having at least some value to make punishing effective, but again, that is common to PoS systems. Another reason the utility token should be valuable is that otherwise the signatories could be contempted to "pause" their participation in periods with high Bitcoin fees (e.g. around Bitcoin's last halving).

The big con is, of course like in most L2 projects, the premine of the utility token NOM. However, at this moment the NOM token is not traded at any exchange, so it's not the typical pump and dump where the utility token is launched and dumped before the main functionality is added. And of course it's possible to think about a no-premine fork

Nomic also doesn't provide a tail emission for Bitcoin miners via merge-mining, a topic we discussed in several threads which could be a long term solution for Bitcoin's "Year 2140 problem". Possibly the protocol could however be changed in a way to make that possible, for example if the sidechain block "production" is changed to a PoW/PoS model.

I disagree here. I'll keep it short because it's OT in this thread: for me Bitcoin and all cryptocurrencies work like platforms (i.e. social networks). The mining cost is not very relevant for the value creation, it's usage and above all demand for the blockchain. If you want a "cost" to speculate on, I think the most convincing metric would be the volume of fiat/other assets being converted to Bitcoin without being immediately converted back ("new buy orders created", for example). So I actually don't see a big difference to PoS coins here.

Correct.

A short remark here: I guess there will be always an equilibrium between the coins "pegged into subnetworks" and those that "stay at the mainchain". And it will be always better to have several subnetworks, above all if we talk about sidechains.

If a subnetwork becomes too important without its underlying blockchain providing a convincing amount of security, this could lead into this subnetwork becoming an attractive target for attackers wanting to short Bitcoin (attacking the sidechain's consensus). So I guess that if millions of BTC are eventually locked into sidechains, we could see community action caring about no one of them becoming too strong, similar to what's currently occuring with mining pools (no one should come close to 50%).

We could speculate that this could even lead to the situation where already strong mainnets which have still some space for transactions could become attractive for "layer-2" mechanisms. This is for example the reason why I created a thread about the idea "Bitcoin on Litecoin" (until now, I conclude that it's possible but would require a lot of development work for the protocol). tBTC on Ethereum (pegged to wBTC) is another example, but Ethereum doesn't really have the capacity to accomodate all transactions of a full-fledged Bitcoin "subnetwork", i.e. working as Bitcoin sidechain. LTC would be a more convincing choice.

Yes, that's an interesting point. So actually I think Sztorc is too fearful of altcoins being able to "dethrone" Bitcoin.

If we talk only about "features" of the scripting language, Ethereum should have "dethroned" it already but that didn't happen. The market thus thinks that either 1) Ethereum's features are not that relevant and/or 2) Ethereum has some disadvantages with respect to Bitcoin. I think both things could actually be true. The disadvantages being, apart from Bitcoin's first mover advantage, the large premine, the not-complete censorship resistance (TheDAO rollback) and PoS as an inferior consensus system.

value/price/market cap flippening:
alot of people think blockchain currency units are created at no cost and so the market can speculate down to zero or up 'to the moon'.. much is true for PoS coins and other silly meme tokens that are based on nothing but drama. however bitcoin does have major cost of block/coin creation cost. the hashrate/difficulty vs mining cost gives bitcoin units real underlying creation cost value which the markets then speculate above, preventing it from going to complete zero(unless the hashrate/difficulty dropped)

for there to be a flippening where another network takes the top spot, it requires some real underlying cost security, meaning that a currency needs to push itself above the underlying cost of bitcoin or bitcoin loses a substantial amount of hashrate/difficulty to drop its underlying cost

currently ethereums cost of creation dropped by 95% when it changed to PoS and is only being held up speculatively by its conversion to bitcoin where traders on the bitcoin side are manipulating the ethereum price to keep ethereum speculative high compared to its cost value.
in short ethereum has alot more chances of crashing to near zero compared to bitcoin because its only due to bitcoin that ethereum is being held up so high

utility/usage/popularity flippening:
currently no subnetwork has more then ~6000 coin pegged so i dont see any subnetwork taking on the majority of usage/utility away from bitcoin.
as for other mainnets, which pretend to offer more/better/faster features, if you look at their market price movements, most just shadow follow bitcoins movements so there is little independent market sentiment separating other mainnets from bitcoin. they just shadow each other due to the arbitrage opportunities of bitcoin.
if we start to see things like ethereum become more price independent and less shadowing bitcoins whim, then it shows they are developing more independence, but for the moment i cant see a flippening happening where a different mainnet gets popular in utility/usage to go full independent and starts to be the dominant mainnet for crypto.. but with thats said, the future can change things

Well I hope you are right, but BIP 300/301 were already created in 2019, and the problem is that there are several high-profile developers skeptical about the concept. Unfortunately I have read no recent news about that to be changing.

Regarding shitcoins becoming useless and disappear, I really doubt it. The incentives for shitcoins aren't that much "that they offer something different" than Bitcoin. For example if you start a simple Bitcoin clone from 0, a lot of people could actually buy it only because they would even make a profit if the coin gets 0.001% of Bitcoin's market cap, even if all the difference is that it has a new genesis block. That's what happened with some of the first altcoins, namely Bytecoin (BTE), but you could say it even about LTC which managed to survive until today in the top-25 altcoins. There are lots of other coins out there having a lot in common, that's also true for the 999 "Ethereum clones". They'll never put Bitcoin's (and Ethereum's) leadership in danger, but they survive.

I think Sztorc's opinion there is of course directed to those that say that Bitcoin is "outdated" and there will be a "flippening", and in this case I somewhat agree.

The issue is that it is extremely easy to build a blockchain today. There are a lot of open source libraries. And then you add a centralized bridge and call it a "L2". Or directly clone Ethereum's Optimism rollup and add a wBTC bridge. That's what happened with most projects I've reviewed on the l2.watch website.

Not that this is bad per se, maybe somebody actually creates an interesting project. But a 50% premined "L2" with no convincing 2-way peg and only vague ideas how this could be decentralized is a no-go for me.

So many l2 projects without any real users. We already have lightning network and it still not wide supported, that's sad especially when you know how fast it is

It doesn't take years for Drivechain and most of the stuff is already ready to be deployed with BIP 300 and BIP 301.
Than you can create any sidechains you want, we could have actual privacy on bitcoin, and most of the shitcoins would become useless and dead.
https://github.com/bitcoin/bips/blob/master/bip-0300.mediawiki
https://github.com/bitcoin/bips/blob/master/bip-0301.mediawiki

Myself I'm not particularly fond of the "layer" buzzword. But it seems to be the most popular at this moment, more so than "sidechain".

And for me it's also different than a simple "bridge". Current "bridges" like wBTC are not tied strong enough to Bitcoin's consensus mechanisms as they often imply trust in some bridge custodian. In other words: if "wBTC" is a bridge, then I'd like another word for a sidechain or another mechanism where no direct trust is required, be it "layer" or whatever. L-BTC if we follow this definition is a bridge though, not a layer, due to the necessary trust in a Federation.

For a "layer" I would personally expect such a strong tie, like provided by mechanisms like Drivechain. I would tolerate however that the layer is based on a set of additional, but decentralized incentives. This means: a decentralized system external to the Bitcoin main chain which rewards custodians to play by the rules and punishes them if they don't, could be enough to classify it as a "layer".

If the "layer" is the contract dealing with the Bitcoin-pegged token (multisig federation etc.), the rest of the chain functionality not necessarily has to be part of the "layer". In my transaction-graph centric "layer definition" the chains are independent from each other. So a chain can without problems contain a "layer" to infinite mainnets. The chains are only the technical infrastructure.

From the current point of view I agree - with current transaction fees I would stay on mainchain, with Lightning as an option for smaller payments in hign-fee times.
Of course the point of this thread however is to find projects which have the potential to change that. For now, still Nomic, Stacks, perhaps BEVM and tBTC are the most interesting ones.
Drivechain is cool but I don't know if it will happen in the next 10 years on BTC. Perhaps if it's first tried on a "real" altcoin, not only on testnets.

I can find only few of them useful but I would never keep any large amounts of coins long term in any of bitcoin sidechains.
It's funny that some people are promoting Lightning Network so much but only 5,122 BTC is locked so far, that is nothing compared to 21 million.
I won't even get into less know sidechains that are making a bunch of false promises.
Instead of using sidechains, it would be much more interesting with drivechain.info.

but many side chains bridge to many mainnets
take liquid for instance.. it has many different tokens/assets/pegged coins. so its not solely a skin of bitcoin, it doesnt just cover bitcoin

i know you are trying to interpret the contracts(federations) within the sidechain which are pegged/linked to a particular mainnet justify the "layer" buzzword. but thats then assuming that a sidechain that operates with many networks is not the layer due to bridging to many networks, but within the sidechain its the contract(federation) that is the (?)layer(?) of a mainnet, thus making it appear that the mainnet must be then within the sidechain if the (?)"layer"(?) is within the sidechain.. it starts to not make sense in that way.

this is why the main community prefer the wordage of bridges. offramps, subnetworks rather than 'layers'(skins)
especially people are not going along with the "ontop"(better) subliminal's too when talking about subnetworks as most subnetworks are less secure then mainnets

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anyway a good stat to update regularly in the top post of topic is how much value in locked utxo's are pegged to a particular subnetwork bridge, as that then shows which ones are populating the most

I actually agree with you a bit about this issue, above all if we talk about sidechains. From a networking point of view, a sidechain is indeed a subnetwork, or in some cases a separate network with some overlap with the main network (if not all nodes on the "L2" chain are also nodes of the L1 chain).

But only a bit

Because if we look at the whole thing from a transaction-centric view, i.e. instead of looking at the node network graph, looking at the transaction graph, then I think the Layer-2 analogy still holds.

If an user pegs-in 1 BTC into a sidechain, and then 1 month later another users pegs-out this 1 BTC after with the "sidechainBTC" (i.e. the utxos created on the sidechain as a result of the peg-in) 1000 transactions were done on the sidechain, from Bitcoin's transaction graph's point of view what you do is bundling 1000 transactions into one (very simplified). The sidechainBTC transactions thus can be considered a layer to the "true BTC" of the mainchain.

Perhaps we can agree on that sidechains can act as a layer for transactions, but they aren't only a layer but actually can have a lot of other functions too, and from a networking point of view they are actually often not really a layer.

i appreciate d5000 taking the time to delve into the wider world of subnetworks so ill give him some merit


but the wordage of the whole L2/"layer" tag is becoming defunct/redundant

its not like most subnetworks remain layers that only wrap around a core network and function solely to secure the enclosed value of that one mainnet.. instead many are subnetworks that bridge between multiple mainnets so thats why the community prefer words like subnetworks and bridges (think subways and highways and bridges with on and off ramps between multiple communities)

the terminology of analogies is not fixed but the "layer" term is getting less and less relevance when most subnetworks start offering access to different currencies and no longer just wrap around and function with one network

as for the definition of subnetworks. is similar/akin to subdomains and also illustrating the analogy that these subnetworks are below the mainnet in terms of security. as many subnetworks will never be as secure as the mainnet, thus a subclass of network security, rather than the illusion/delusion of top quality penthouse, top security, leader, subliminal word garbage done for fame stealing and false promising of being 'solutions'/better than the mainnet

Last issue of the l2.watch reviews. This time I'll cover Rollux, Sovryn, U Protocol and MintLayer.

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Rollux is an Optimistic rollup mentioned, but still not reviewed on BitcoinLayers.org. Its native chain is not Bitcoin but Syscoin, a quite old altcoin (from 2014/15, if I remember well) which is merge-mined with Bitcoin. According to their website, it "introduces DeFi, NFT’s and cheap smart contracts". So the data to reconstruct the transactions and create proofs is stored on an altchain. This is not bad per se, but as the altchain itself was premined, it doesn't exactly improve the decentralization, and also of course there may be additional attack vectors in comparison to a rollup settling on Bitcoin. It also relies on  "Syscoin’s masternodes" "to provide finality", i.e. the Syscoin masternodes vote about the proofs.

At this moment the rollup is centralized, only the Syscoin foundation runs a sequencer node (i.e. produces blocks on the sidechain). According to the website this is temporary ... let's see. There seems to be currently no decentralized Bitcoin bridge either. While the project looks a bit more serious than those coming from the Ordinals/BRC-20 space, at least in the current state it's also not really interesting.

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Sovryn uses currently the Rootstock sidechain, which is still federated, for their Bitcoin-backed stablecoins. In the future, they claim to be developing a Bitcoin bridge using an Ethereum-based Optimistic Rollup called BOB ("Build on Bitcoin") as its base. Website looks nice but the project in its current state is not a Bitcoin sidechain but a simple altcoin.

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U Protocol claims to be a "Layer 3" for Bitcoin. After a lot of projects which didn't have even a Bitcoin bridge, it has at least one - the Bitcoin "synthetic currency" uBTC. Arbitrum is mentioned on the start page of the website so probably Optimistic Rollup technology is used. There is also an utility token called YOU.

The Bitcoin bridge is however unfortuntately also not really a Bitcoin bridge. The uBTC coin is backed by Lido Staked Ether and BTC.b, "a decentralized Bitcoin (WTF?) bridged to EVM via the Avalanche Bridge" according to their website. The model thus looks very similar to BVM where wBTC was bridged instead of BTC itself.

Thus again, we have not really a Bitcoin sidechain but this time a combined Avalanche and Ethereum sidechain. But at least a sidechain with a Bitcoin bridge, which is more than most of the products on l2.watch do offer. I'd have to analyze the BTC.b bridge to know if there's some interesting tech behind it.

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MintLayer is one I forgot to review. It's however even less interesting than the other ones: simply a PoS blockchain allowing atomic swaps with Bitcoin. A bridge is not mentioned on their website. Tokenomics are extremely ugly and  shameless namedropping ("Von Neumann" and "Lovelace" testnets) also leave an extremely bad impression.

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In conclusion to my reviews of the projects with working "mainnets" on L2.watch, it was really disappointing. At least, 2 or 3 projects have some interesting elements, and I will also review in the future the tBTC Ethereum bridge (not to be confused with testnet Bitcoins, of course!) and perhaps the BTC.b Avalanche bridge. But L2.watch should really change the way they categorize the projects. Most projects are not sidechains, and those that are, are not more decentralized than the well-known federated sidechains Rootstock and Liquid. The BitcoinLayers project is thus totally correct - most "L2s" are probably marketing technobabble.

Fifth and penultimate group of short reviews of the sidechain/rollup chains shown on l2.watch as having a working mainnet: Kadena, Merlin, MVC and Map Protocol.

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Merlin Chain is one of the sidechains covered on the Bitcoinlayers website linked above. And unfortunately their review is quite clear: at least in the current state it seems to be completely centralized (the committee is selected by the admin, the sequencer "producing blocks" is a single node).

It claims to be a ZK rollup and is built upon Polygon technology. But according to BitcoinLayers it seems to be unclear which chain is used for settlement. It seems not to be Bitcoin (nor Ethereum) at least. Another red flag is that not all code is open source.

Merlin plans to transition to a to another rollup technology, more in line with Optimistic Rollups, on Bitcoin.

Another one which currently doesn't look interesting, even if it seems to be supported by some big names like OKX and ViaBTC.

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Map Protocol is another older project, launched in 2018. It claims to be the "Layer 0 of Bitcoin L2s, aimed at achieving interoperability among various Bitcoin L2s". Or taking the buzzword for such chains: an "omnichain".

A superficial high-level description of the architecture is here. It has a "Relay Chain" operated by a PoS algorithm, and a bridge for BRC-20 tokens based on an own Ordinals-based protocol called BRC-201  .

The "omnichain" design is explained a bit deeper in the whitepaper. Basically it seems to be a network of light client operators of different blockchains forming a committee. These "maintainers" create ZK proofs that the blocks of the origin chain are valid.

There is however no good description of the Bitcoin bridging mechanism with an incentive analysis. Thus I'm also quite skeptic about this project. In general I conclude it's also a design similar to Thorchain, where the incentives for the committees to operate honestly are only generated on the sidechain. That their technical documents are bloated with trivialities doesn't improve the general impression.

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Just for the records, the following two protocols listed on L2.watch seem not to be Bitcoin sidechains:

Kadena does use some sidechain technology in its Chainweb concept, but there seems to be no Bitcoin-pegged token - it's a sidechain architecture enabling an altcoin to be created on several chains instead of one. While not sounding uninteresting it's OT in this topic.

MV or Microvisionchain is also seemingly not really a L2 project. It's main feature is the "Smart Contract on UTXO" functionality, i.e. the blockchain is based on UTXOs but anyway supports turing-complete smart contracts. Again we see much technobabble, but one thing is unique: they opt explicitly for the "proven" "Big Block" model It has a bridge but for ETH, so it's also OT.


P.S.: I have linked the reviews of the last posts in the OP and categorized them into different classes according to the potential they have.

Thank you for that interesting screenshot and the Blockspace article! That's indeed the impression I'm getting too, that most "L2s" are more or less traditional shitcoins with some wBTC-style bridging, but few have really mechanisms qualifying them as a "sidechain" or "rollup" with a convincing, decentralized 2-way-peg.

I've done some googling and found BitcoinLayers.org, which seems to be the origin of the screenshot. It's a very interesting website, and they've done basically what I'm doing in this thread but with a much more systematic approach. They do a risk analysis of a couple of known layer-2's, their categories being Bridge custody, Data availability, network operators and settlement assurance (that seem to be these green, yellow and red icons).

It's really shocking that apart from Lightning all other projects have at least one point marked in red. This could of course mean that the site is run by "Lightning network fans", but I think in general the criticism they do on the existing projects is mostly valid. Have to dig a bit deeper though.

PS: Ah, interesting, so ZKsats already is known as a scam according to the Blockspace article? Then of course it won't be covered by my "Observer" posts. L2.watch should then also remove them ...

PS2: Didn't find really info about the ZKsats rugpull, but they went silent on X/Twitter two months ago, so this may be the red flag here. There are also some users complaining in this post.

I found one article claiming that most Bitcoin Layer solutions are just marketing scams.
We could argue if that is true or not, but there is one interesting screenshot in this article that shows all Bitcoin sidechains compared.
I am looking to find website origin of that screenshot, if someone knows about it please post link below


https://blockspace.media/insight/most-bitcoin-layer-2s-are-marketing-scams/

Let's go for the next group on l2.watch.

ckBTC on the ICP altcoin network is supposedly a decentralized bridge, converting ICP in a Bitcoin sidechain. But there is no good technical explanation available, much less about the incentives. There seem to be smart contracts (called "canisters") which track the Bitcoin network, probably with a SPV client (see Bitcoin Integration). These so-called "ckBTC minters" track if BTC users spend Bitcoins to an address controlled by them, and create a ckBTC token on ICP. While if a ckBTC is burnt, the ckBTC minters redeem it on the BTC chain.

The most ridiculous thing here is that they claim to use "no middlemen" and "no custodians", but - somebody has to operate the ckBTC minter contract. This is the middleman, FFS!

For me that sounds too easy to be convincing - if this was that easy, it could have been implemented 10 years ago in any altcoin, at least on any offering turing-complete smart contracts. I distrust ICP in general for the high amount of technobabble they use, so this "sidechain technology" doesn't improve my impression here.

In addition, I found this (lol):

Source

Oh. So it does KYT and is decentralized? How does this magic tech work, is there some SchellingCoin-based blacklist for example? Or simply the founders maintaining a centralized blacklist ...

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Libre doesn't seem to be really a sidechain, even if they talk about "improving" scalability on their website. They instead use a bridge called pNetwork. Nothing more to expect from a "tech" coming from the Ordinals/Runes sector, despite the "beautiful" name .

Quote from the pNetwork whitepaper:

They seem to be transitioning from a completely centralized bridge to an optimistic rollup approach, but the whitepaper lacks a description how this would work with Bitcoin.

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Nervos Network is a chain I have stumbled upon somewhen in the past (Ah I remember now, it's the guys with the RGB++ protocol). It's a relatively old (2018) PoW altcoin with smart contract functionality. But even if they are listed on L2.watch as a Bitcoin sidechain, this functionality seems not to have been implemented yet. It seems to be in an early state of development.

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And finally Gelios, another EVM-compatible "sidechain" and "the first Runes-based blockchain" (looks good right?). Their "bridge" has one characteristic I haven't seen before: they encode some data via OP_RETURN when doing a peg-in (see here), for example the Ethereum address of the receiver. But again, no info is provided about how the incentives of the bridge work. It's probably a completely centralized bridge like wBTC.

Edit: Gelios seems to be extremely dubious, see this post. However to label it as a "scam" I need more info.

Again I found nothing really interesting here, but if my conclusions are wrong I'm grateful for any feedback The purpose of this Sidechain Observer is "not" to denigrate projects as "shitcoins", but actually to find interesting approaches. But the success has been limited until now, so I can actually understand why most Bitcoiners are still not really interested in sidechain technology.

The following protocols with a working mainnet are still missing: Kadena, MVC, Map protocol, Rollyx, Sovryn, U Protocol and ZkSats (seems to be a scam, see article linked by dkbit98 in the post below).

Elastos is the next project in my list to present here. It's a L2 project initially launched in 2017, now having archieved mainchain stage.

The consensus is based on merged mining with Bitcoin, with "standard" block rewards through the ELA token, including halvings and a capped total supply. A quite "traditional" altcoin up to this point.

For Bitcoin scaling, the BE-L2 technology is presented as a solution (the link leads to the whitepaper). However, it seems that the Bitcoin stay on the mainchain. They can be used, through zero-knowledge proofs, on the sidechain for smart contracts, for example for lending contracts and other DeFi apps.

So in general I think this is not a full-fledged sidechain but a project addressing some limited scaling use cases. In contrast to the category it was put in on l2.watch, it seems also not to be really a rollup, more a kind of atomic swap technology. The technical concept looks okay though. But again, we have tokenomics with a centralized character, with 50% of the tokens pre-allocated. Another more or less disappointing project, but regarding its market cap one of the bigger ones.

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Edit: Decided to expand the post because there are various projects on l2.watch which do not really deserve an own post, as they aren't really Bitcoin sidechains. Just to mention them here so to help people which projects on that site aren't that interesting.

CoreDAO is one of these. It's basically a DPoW altcoin anchored on the Bitcoin blockchain. Again we have shameless namedropping ("Satoshi Plus Consensus") and a highly centralized distribution where only about 40% are available for miners and through other rewards. There was a substantial airdrop (25% of total supply) though, but this doesn't necessarily mean the founders didn't benefit from it.

The Bitcoin bridge called coreBTC. To "move" BTC to the Core blockchain, you can select a custodian (called "lockers") from a list which will have to provide a collateral and are incentived to return the Bitcoin if there is a peg-out. So if I interpret it correctly, it works a bit like Thorchain. But on a whole this doesn't look really interesting, it's a mechanism you could build on most blockchains.

Ok, let's continue with BEVM. It seems that this sidechain is a little bit more interesting than the two I covered in the last post, so I'll dedicate a whole post to it.

Like BVM (do not confuse both!) this project's goal is to provide an EVM-compatible environment for dApps which can use Bitcoin for smart contracts and as "gas". The consensus algorithm is based on PoS, with up to 1000 "consensus nodes". Addresses are Ethereum-style, and Ethereum tokens can be swapped to the chain. It's build with the Substrate blockchain framework. The Whitepaper can be found on Github.

Now to the most important part: how does the bridge (2-way-peg) work?

The PoS consensus nodes manage the bridge as custodians. When a peg-in is performed, the user transfers the Bitcoin to the custodians. All custodians run a Bitcoin light node which is part of the consensus, and thus they can prove that the transaction occured on the mainchain. A peg-out is performed by a BFT vote. Each peg-out intent is checked by the custodians and only if 2/3 of them vote that the peg-out is legitimate (i.e. the ancestry of the pegged-out coins goes back to a peg-in and there was no double spend) one of the custodians creates a transaction to the user who pegs out.

This looks very similar to Thorchain: The chain works purely by the incentives the PoS consensus on the sidechain generates. However, the docs are not as detailed as I would have liked. They don't answer the following questions: 1) to which node the peg-in is performed, 2) which kind of transaction is generated in the peg-in (multisig? with whom?), 3) how the node is selected which pegs-out the coins on the mainchain, and also 4) what happens if a node misbehaves?

So I'll continue to investigate about this one. I'm not totally convinced it's a serious project but it could be one - it claims to have got investments from ViaBTC, for example.

What does not look that good is the tokenomics. 50% of the coins are beneffitting the founder team (15% direct team allocation, 20% investors, 15% foundation). Validator incentives make up only 22%. This is thus also a project where I would propose to fork it with 100% validator incentives if it works

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PS: I found this blogpost which explains the peg mechanism a bit:

- The PoS consensus nodes form a multisig federation with up to 1000 nodes thanks to Schnorr signatures. Instead of a traditional multisig structure a MAST (Merkelized Abstract Syntax Tree) is used.
- If an user pegs-in into the sidechain, he sends the BTC to this federation.
- For a peg-out, 66%+ of the federation members have to "vote" for this peg-out via multisig consensus.

Not exactly a very complex solution and basically the same what Liquid is, only with far more members and driven by PoS consensus.

About the slashing mechanism I didn't find anything. What if 66% of the PoS federation collide to cheat? Is there any mechanism including Bitcoin mainchain proofs?

PS2: This however is a quite dumb blog post, so I question the technical ability of the BEVM team a bit. WTF, "Before the explosion of BRC20 tokens, few could have believed that it was possible to issue tokens on Bitcoin." Who wrote that utter bullshit?

I'm currently examining the projects which already have a mainnet on L2.watch and are rollups or "traditional" sidechains (things like "wrapped tokens" aren't really interesting here). The big question is: Did they already solve the problem with the 2-way peg?

Ok, let's go through them one by one. Today I'll cover the first two rollups with active mainnet: Biop and BVM.

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Biop is a rollup using the Optimistic Rollup technology we know from Ethereum projects like Optimism (they claim to be the first for Bitcoin). The mainnet was launched in Q1 2024.

There are two characteristics of this project I don't like that much: 1) they seem to come from the BRC-20/Ordinals space, and 2) they have a premined token where no less than 19% were allocated to the founders, and 20% to investors (3,x% in an "IDO), plus 10% which went to a "Foundation". Quite centralized even for the token space, as 49% of the tokens benefit the founders in some way, so I'm very skeptic that this rollup could really attract Bitcoiners.

The Whitepaper explains its inner workings. The chain uses Bitcoin's security and additionally has a PoS consensus. "Sequencers" create blocks on the sidechain, and "validators"' task is to provide fault proofs in the case a Sequencer includes an invalid transaction; so this Sequencer can be slashed. They have a virtual machine for turing-complete smart contracts called BVM (not to be confused with the other rollup!).

I haven't found anything in the whitepaper how their Bitcoin peg/bridge mechanism works and if it's already operative. Yes, I know, optimistic rollup, but how exactly are transactions written "back" to the Bitcoin blockchain and when? So it's a bit hard to take this project seriously. It's also not clear what the different versions of BIOP mean. To me it seems like an altcoin where only perhaps tokens like BRC-20 can be transferred to. Perhaps somebody can enlighten me ...

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BVM (Bitcoin Virtual Machine) is another Optimistic Rollup, or it seems to be a set of different rollup chains: one dedicated to GameFi, one to AI, one to DeFi, and one to SocialFi. And again: they "use a technique akin to that of Ordinals to inscribe data". Good start  They have even a part of the whitepaper which sounds exactly like the Biop whitepaper: explaining that an Optimistic Rollup is "a fancy way of describing a blockchain that piggybacks off the security of another blockchain". Do they copy everything from the same source?

But at least they seem to have a Bitcoin bridge that works, even if it is quite convoluted - see whitepaper. To "deposit" Bitcoin to BVM, you first have to go through WBTC (WTF???), i.e. a centralized Bitcoin<->Ethereum bridge. The same is true for withdrawals: you first exchange your BTC on the sidechain to WBTC, and then to BTC via the centralized bridge.

So this is basically a WBTC sidechain, not a Bitcoin sidechain.

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I'm quite disappointed from these two projects I must say. Let's hope for the better in the next edition(s) of this Observer. Next ones will be BEVM and Elastos.

Of course, everybody having something to share about an existing or future sidechain project, or has experiences with one of the projects in L2.watch, is invited to participate in this thread

Thank you, very helpful website. Some of the projects described as "sidechains" would not meet my own definition (for example, they list Sequentia, which has no peg at all and for me is simply a "Bitcoin-anchored" altchain like Komodo) but others do and generally the site seems a good starting point too. So I've included it in the OP.

There is also L2.watch which lists a quite large list of projects and ideas (included it now in the OP) and the state of their development progress. They include "wrapped token" and other centralized mechanisms too, but there are also some interesting projects I didn't know about.

For example there is BEVM, which claims to work with Taproot contracts and according to L2 Watch is "operational". They claim also to be more decentralized than Stacks. I have however still not understood how their 2-way peg works; in their whitepaper they evade the term it seems and instead talk about "interactions". If someone knows BEVM better and can say if it could help with Bitcoin decentralization or it's just another vapourware/centralized project, more info about that project is welcome!