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Hi all, this is Burak. Feel free to ask me anything about Ark. Ark is a new privacy-preserving Bitcoin layer-two idea for those unfamiliar. I would love to address all of your questions or concerns you might have. Stupid questions are welcome :)

When do you think will be available some testing code for all this ark?

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I'm currently assembling a team of Bitcoin devs and wizards with the goal of building a prototype. We aim for a rollout later this year on inquisition signet or liquid.

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Liquid?! Ya don’t say!

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It has covenants, man. Can't deny that..

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It has covenants, man. Can't deny that..

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What's the greatest challenge you see to developing Ark (aside from CTV activation)?

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It's probably the bootstrapping phase. Ark uses a shared utxo model, which by design, gets cheaper the more people participate in the system.

Considering there won't be much usage in the early days, transacting on the protocol will be relatively expensive.

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Do you regret the manner in which you broke lnd? Why or why not?

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Bitcoiners loved and appreciated what I did. I am sure I would have regretted it if I had a pushback from the community.

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How did you break lnd?

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On October 9, 2022, Burak from Bitmatrix (a swap tool built on the Liquid Network) created and broadcast a transaction to the main Bitcoin network, spending a UTXO with a Tapscript multisig with a 998-of-999 threshold. This transaction had 998 individual signatures in the witness field, and was almost 0.1 MB in size, and kind of hilariously, reused the exact same public key for every one of the 999 participants in the multisig. This transaction caused a massive disruption for the Lightning Network by exposing a bug in LND and btcd (an alternative client for the Bitcoin network).

Source: https://bitcoinmagazine.com/technical/learning-from-the-lnd-bug-on-lightning

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How would mempool fare if a large ASP goes under and all vTXOs need to get on-chain? Is there always enough time to start unrolling your tx with/without CTV congestion control?

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We plan to use Rubin's congestion control tree idea for vTXO closures. In a disaster case, it could take years to withdraw from the tree, although the four-week locktime is over.

https://rubin.io/bitcoin/2021/12/09/advent-12/

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But even with Congestion Control there would still be a time-limit for lots of tx: one per pool tx that has at least one unspent vTXO. They are smaller than unrolling everything, but there are still ~500k 5-second periods in 4 weeks. Or could they be batched in some way?

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Will an ASP be able to sweep the funds after the 4 weeks but before all users have been able to claim back their funds for years?

I couldn't imagine having funds locked up for years either way....

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What help do you need most with respect to Ark?

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I think there are a lot of misconceptions about covenants. There is certainly room for help in educating people on covenants and their benefits.

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https://bitcoinops.org/en/topics/covenants/ seems a good starting point. Any other resources you'd recommend?

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You saw the LN as being too difficult and complicated for the new user due to necessity of incoming liquidity, failed transaction, etc. Are you confident Ark will be a seamless, simple experience for a new user?

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Absolutely. That's what I designed Ark for. Ark brings custodial-grade UX to self-custody.

Ark offloads complexity from end users to service providers. End-users do not need to take care of their channel management/liquidity. Everything is abstracted from the user, yet the user retains self-custody.

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What happens if a coin-join round "fails'?

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The vTXOs that would have been consumed and created by that coinjoin round are not consumed and not created. For the round to fully fail the ASP probably needs to spend the input they were planning to use in that round in another on chain transaction, which then gives the participants certainty that the coinjoin will never happen, and frees them up to spend their vTXOs in another round.

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Follow-up question.

What would happen if the transaction gets stuck in the mempool. Can the ASP do an RBF on the transaction or would it require all participants in the coin-join to sign the transaction again.

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The ASP cannot RBF, but could CPFP or pay a miner out of band to include a stuck coinjoin transaction.

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Eventually someone will need to use it as inputs and they're going to have to pay fees using CPFP, I suppose. Until then, Ark txs will be public so all participants in the round will have an incentive to keep it around to broadcast it if needed.

It does allow the ASP to double spend the input coins though as long as the tx is unconfirmed. Supposedly that can be mitigated by using one of the nonce-fixing strategies.

How much liquidity do you expect a typical ASP to have? Perhaps also explain how you plan to lower the requirements (that old VTXOs will be able to get more efficiently redeemed).

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ASPs can customize their fee tier configs and vTXO liveness delta preference according to fee market & liquidity conditions.

One must own a large chunk of BTC to run an ASP infra. Otherwise, its better to join an ASP federation.

Although intense capital requirements, overall, Ark uses liquidity as efficiently as Lightning since recipients are always one hop away from the senders, unlike Lightning, where the liquidity must be deployed on every single hop.

There is also room for liquidity optimizations: #192143

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Dangers of centralisation?

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Does a single user's unilateral exit force everyone in their VTXO set (meaning all users of the ASP who made a payment in that 5 second interval) to chain? If so this could be a type of DoS attack. The single attacker pays an onchain fee, now thousands or tens of thousands of people have to also. Maybe miners even profit from this attack? Pay a single fee and send thousands of fees to miners?

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vTXOs in a shared UTXO are self-isolated from each other. One vTXO exiting tree doesn't affect the others.

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This wouldn't be a DDOS attack. Everyone else's vtxo is locked into the sharedUTXO which is being paid to the ASP until the 4 week timeout.

When the remaining members of the shared UTXO come back online at the 4 week mark, the ASP pushes them into the next coinjoin round to create another sharedUTXO with other people who are entering in that round.

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Do you foresee bitcoin moving to larger blocks in the future?

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No, at least not in my lifetime.

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591 sats \ 1 reply \ @kr 12 Jun 2023

How did you decide on the name Ark?

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I named it Ark because it resonated a lot with Noah’s Ark. Ark is here to save plebs from the dangers of chainalaysis companies and custodians.

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  • op_ctv
  • sighash_anyprevout
  • op_cat
  • something else

Which covenant soft-fork or combination of them would be most optimal for building the best Ark?

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My favorite combo is OP_TXHASH + OP_CHECKSIGFROMSTACK.

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Interesting - so the (slightly) larger on chain size is more than compensated for in your mind by the flexibility?

IIUC these two can do everything that APO + CTV can do with just a few "extra" witness bytes in typical usage, and TXHASH+CSFS can also do many things that CTV+APO cannot.

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I believe op_ctv's byte-efficiency would be greatest, but not positive.

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Do you have concerns around the potentially centralizing effects of ASPs?

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Trustlessness is a binary option, not a spectrum. There is no such thing as 'more trust' or 'less trust'. It's either trustless or not, and Ark falls into the 'trustless' category.

Decentralization, on the other hand, is a spectrum, yes.

Decentralized β‰  Trustless.

Protocols/services can be:

  1. Centralized and trustless (LSPs & ASPs).
  2. Centralized and trusted (WoS).
  3. Decentralized and trustless (Bitcoin).
  4. Decentralized and trusted (Fedimint).
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Decentralization is just a tool for censorship-resistance and self-custody. Decentralization is not the end all and be all of all things.

Both traits are preserved through ARK, so IMO it's not a big concern.

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Do you see any potential solutions to addressing the liquidity requirements that doesn't include borrowing bitcoin from lenders and raising ASP fees? Something in the design we can do to potentially make available bitcoin from ARK depositors that the ASP could immediately use to fund transfers?

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There is room for two main liquidity optimizations.

  1. vTXO delta auto-adjustments vTXO liveness delta can adjust to liquidity conditions. i.e if we cut the vTXO liveness delta by half (2 weeks), we also cut this liquidity lockup requirement by two, and so on.
  2. A revocation logic I'm working on a revocation logic where a set of users in a shared utxo give up their ownership of vTXOs by revealing some secret. ASPs can efficiently redeem these funds without affecting the remaining participants before the four-week locktime is over.
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Did you get VC funding already? :)

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I plan to build an infrastructure firm, similar to Lightning Labs play, to build & ship Ark. I'm in talks with a couple of venture capital firms.

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I've noticed that lightning doesn't work well when using Tor. It seems that routing fails and I'm unable to transact.

Will Ark suffer similar problems?

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It could potentially affect the CJ round. But outside of that, no.

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Yeah, Tor makes coinjoins super tricky to coordinate. We're considering less privacy-preserving but more efficient alternatives for the transport layer.

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1.We'll have PoC around Ark?

2.Ark is compatible with Nostr?

3.What's scenario Ark with PayJoin?

4.It will have VC influence like LL, Blockstream?

5.Why CTV is important for Ark?

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1.We'll have PoC around Ark? Please don't take my word for it, I've been historically wrong with deadlines, but it's fair to expect a prototype later this year.

2.Ark is compatible with Nostr? Yes, we plan to use Nostr as the transport layer for Ark; for things like out-of-band communications and coinjoin coordination.

3.What's scenario Ark with PayJoin? TBH, I don't really know what a PayJoin is and how it works.

4.It will have VC influence like LL, Blockstream? VC influence on the company, yes. VC influence on the protocol, no.

5.Why CTV is important for Ark? We need CTV (or a similar proposal) to make Ark work non-interactively. Non-interactive as in receiving funds on the go (without being online).

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Excellent. Thanks for answers! :)

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Wen ark?

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two weeks β„’

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The sender of the payment gets something like a preimage from LN that proves payment was successful. How does that exactly work?

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The public key of the intended vTXO is tweaked with a payment commitment that reveals the payment proof when spent. Tweaking details can be found here:

https://github.com/ark-network/boats/blob/main/01.md

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What kinda of soft forks do we need to enable a non-interactive ARK?

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Either APO, CTV, or TXHASH. Some opcode combinations also give you the same functionality.

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Menemen - with onions or without?

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IF it's a proper one, with onions please. without onions otherwise.

it's a BIG IF though.

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Why not make a pool every Bitcoin block? And reduce the lock-in time to one week or two instead of four?

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What did convince you to join the big blockers first?

And at which point did you realize you made a mistake?

edit: Oh, these are not questions about Ark. I hope you don't mind. If you do, feel free to ignore haha

You might get asked this a lot

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I thought Bitcoin could only scale on the base layer, as Lightning initially seemed to be a flawed design. Over time, I started exploring the Lighting space more closely and realized some of my objections were addressable. Eventually, I dedicated myself to improving Lightning, which evolved into a distinct new layer two protocol.

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it's called "ask me anything"

What's your favorite pokemon?

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Maybe I took this too serious, haha:

Feel free to ask me anything about Ark
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1090 sats \ 1 reply \ @k00b 12 Jun 2023

If you can get all the new opcodes you need, what might prevent Ark from being successful?

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A better Ark.

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Do you feel you have the adequate resources to build something of this stature? Or are you coming up with it as you go along?

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Will Ark replace LN or complement LN?

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How can we self custody in Ark? How would it look like for a not so techie user?

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The people programed that the segwit activate the inscribtion but not acknowledge that the taproot make it more eadir to inscribe it , it is very risky to change the conseus to make some cool stuff 🀣

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How do you imagine ARK being used? For daily payments? Or more of a savings account?

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From an end-user standpoint, Ark is both great for savings and payments.

Ark is great for savings because you can own (and transact) BTC without demanding Bitcoin block space.

Ark is great for payments because you can pay invoices, as it's interoperable with Lightning.

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Got it. So it wouldn't be an onchain txn for the lightning payment. Is that right?

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Any good video about ark?

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Why are you trying to reinvent Monero ?

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𝐇𝗼𝐰𝐝𝐲 𝐝𝗼 ? 🀠 πŸ‘‹

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What would happen if an ASP runs out of liquidity? I know I can take my VTXO and redeem it, so not too worried about that side, but realistically what would be an ASP approach to this? it seems like the only choice would be to wait until more funds can be unlocked from the 14 days lockup period, right?

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ASPs would proactively manage liquidity - they have visibility into the flow of funds from expiring pool transactions, and would likely pursue lines of bitcoin credit to bridge times of low expiration flow.

The ASP can also manage liquidity fees to discourage users from making high liquidity requirement payments in times like that. For example spending large vTXOs costs more liquidity than spending small, so the ASP may encourage users to consolidate their small vTXOs to make payments at times of low liquidity. Opposite of on-chain bitcoin in that way where ASP fees being high means its time to consolidate, and ASP fees being low means it's time to consume large "costly" vTXOs.

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Do you foresee Ark as a payment system, or do you think of VTXOs as a method of opening Lightning channels for payments?

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Has the protocol evolved from when you first released the www.arkpill.me/deep-dive page? If so, will that page get updated or should we follow the Github specs for updates? I like a good spec, but I did find the diagrams on the arkpill.me page helpful

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How much capital are you seeking and how does Ark plan to make money / investment returns for its VC partners?

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Que lo motiva a regalar coins

What are confirmation times like on Ark? Reading Ruben Somsen's explanation it seems you need one confirmation on-chain for an Ark transfer, but you could trust that the pool provider doesn't double-spend before it's confirmed.

So would it be safe to send someone funds via Ark and for them to accept it before the next block (or several blocks of confirmation), and also be able to continue to spend those funds into even more transactions

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Which programming language are you going to use for your Ark implementation?

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Do you expect to replace the network effect already acquired by the LN?

If not, what is the goal of ARK?

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Can you ELI5 what ARK is and why it differs from LN?

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I don't know what Ark is. What are the differences between LN and Ark?

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We not going to change the conseus

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I've seen claims that Ark requires 1/256th of all blockspace. Is that true? If yes, who pays for it? If not, what was that about?

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There is a new on-chain transaction i.e every five seconds, so yes, Ark constantly demands bitcoin backspace. I consider this approach footprint-minimal as we can fit thousands of transfers in this transfer period.

Since Ark is based on a shared UTXO model, on-chain fees for the shared UTXO are shared among all other participants.

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What is the main goal of creating ark?

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Scaling self-custody to billions.

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Don't play in consensus , dev make taproot and faciliting the inscribtion we don't know this ark shit is going to do

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You're probably mistaken. SegWit enabled inscriptions, not taproot.

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In Ark, is 1 connector used to gain custody of multiple vTXOs? I was a little confused about this because in the whiteboard video it looked like 1 connector was needed for each redemption of a vTXO.

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Connectors output is also a tree of connectors. There is a 1:1 mapping from a connector to an anchor. I used one connector in the whiteboard session to keep things simple.

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Do you believe Ark+LN can realisticly put a sat in every hand?

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Yeah, that's the goal. A few hundred sats, ideally.

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Do you think there will be a dominant second layer, if so which one will it be?

Also, do you think the same people will use Lightning and Ark are mostly only one of them?

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edit: Typo. Wanted to say:

Also, do you think the same people will use Lightning and Ark or mostly only one of them?
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What motivated you to create Ark?

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I've always been obsessed with scaling Bitcoin to the entire planet, although realistically thinking in the end, this is probably not what will happen.

I've been seeking the perfect solution to scaling, and changes are high that Ark might be it.

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