Crypto News
What the heck is CatVM?

Taproot Wizards released a cartoon yesterday called CatVM. I will not refer to it as a whitepaper, those are real academic documents for adults. In the cartoon, interspersed amongst the absurd childish narratives, were a few valuable technical insights regarding different scaling proposals in the Bitcoin ecosystem. Of course, in true cartoon fashion, buried between wild exaggeration and embellishment.
The end goal of the cartoon was to propose a new mechanism for moving in and out of scaling layers built on top of Bitcoin. To disentangle that actual proposal from the cartoon, we’ll have to break down the two pieces involved.
The Building Blocks
Rijndael’s first OP_CAT experiment was constructing a vault, a scheme that allows a user to create an intermediate “staging” transaction to withdraw their funds from the vault. This kicks off a timelock, during which they can at any time send their funds back to the vault or a secure cold storage wallet, and after the timelock the user can freely withdraw the funds to the destination they chose when beginning the withdrawal process. These are the only two ways bitcoin sent to the vault script can be spent.
Explaining the full mechanics of how this is accomplished is essentially an article in itself, so I’m going to do something I usually don’t and hand waive this away as “magic.” (Explained here by Andrew Poelstra) What this “magic” allows you to do, by creating non-standard Schnorr signatures and with the help of OP_CAT, is to build the transaction the signature check is against on the script stack. This lets you enforce that certain parts of the transaction are exactly as defined ahead of time. It also allows you to put the output from a previous transaction on the stack in the process of building the transaction spending it, meaning you can compare outputs from the spending transaction against outputs from the previous transaction. This allows you to guarantee by comparing them that certain parts of the previous transaction’s outputs match certain parts of the new outputs. I.e. the script, or an amount. So you can “carry forward” parts of the old outputs into the new ones, and enforce that.
Something else you can do with OP_CAT, which did not need Rijndael tinkering and experimenting with to prove, is verify merkle tree branches. Because you can CAT stack items together, and Bitcoin already supports hashing data on the stack, you can slowly build up a merkle tree root from a leaf node with the interior nodes. Hash two pieces together to get one hash, hash that with the pair hash, and so on. Eventually you get the root hash on the stack. You can then compare it with OP_EQUAL against a predefined root hash in the locking script.
Unilateral Withdrawal
These two building blocks are enough to facilitate a unilateral withdrawal mechanism from a group shared UTXO. A merkle root can be embedded in a transaction using OP_RETURN or another mechanism that commits to a leaf node for each user. The UTXO script can be structured so that any user with a balance can attempt to withdraw it. To do so they would provide the merkle branch committing to the amount they are entitled to, the authorization proof such as a public key to check a signature against, and construct the transaction on the stack to verify the appropriate conditions are met.
Similar to Rijndael’s OP_CAT vault, this withdrawal transaction would function as a staging point. User funds would be restricted by a timelock, and they would not be capable of completing the withdrawal until it expires. At any time before the timelock expires, any other user can create a fraud proof to stop the withdrawal and shove funds back into the group UTXO script. They can do this because of OP_CAT’s ability to verify merkle trees. If someone has used a specific merkle branch to withdraw funds from the UTXO before, then that was included in a block somewhere. By constructing a transaction containing the SPV proof of that transaction inside an actual block, which can use OP_LESSTHANOREQUAL to verify the blockheader meets some minimum difficulty, they can prove on the stack that the merkle branch was used before. This allows duplicate withdrawals to be prevented.
In addition to this, because you can use the “CAT on the stack” trick to ensure specific pieces of a previous transaction must be included in the next, you can guarantee that the current merkle root is carried forward into the next transaction after a successful withdrawal. You can also guarantee that change from the withdrawal goes back into the group sharing script. This guarantees that after one user withdraws their funds, the change UTXO is locked with a script that allows any remaining user to withdraw, and so on. Any user can unilaterally withdraw their funds at any time in any order, with the guarantee that the remainder of funds are still accessible to the rest of the users.
The VM Part
Readers should be familiar with the basic idea of BitVM. You can take an arbitrary computation and break it up into each of its constituent pieces and embed them in a large taproot tree, turning that computation into a back and forth challenge/response game. This allows you to lock bitcoin with more complicated conditions than is directly supported by bitcoin script itself. The only real shortcoming is the need to craft a massive amount of pre-signed transactions to facilitate this.
The requirement to use pre-signed transactions is so that in the challenge/response dynamic, you can guarantee that coins are spent back into the large taproot tree encoding it unless an exit condition one way or the other is reached. OP_CAT and the ability to “carry forward” data from previous transactions allows you to guarantee that without needing pre-signed transactions.
So not only does this scheme allow any user to unilaterally exit on their own, it also allows locking conditions supported by a second layer that are not supported by Bitcoin script to actually be enforced in the withdrawal process. I.e. if some coins were encumbered by a smart contract the base layer doesn’t understand, and then withdrawn from the second layer, those more complicated conditions could still be settled correctly on the base layer as the coins are withdrawn.
The Missing Piece
One thing that OP_CAT does not enable is updating a merkle tree root representing user balances off-chain verifiably. It can enable an already committed state to facilitate unilateral withdrawals, but that is because a whole section of the tree is actually put on-chain and verified. To update that root off-chain by definition means you are not putting the data on-chain. This represents a problem. There is no way with just CAT to efficiently verify that all changes to the merkle tree were authorized properly by the relevant users.
Someone(s) has to be trusted, and by the nature of things capable of spending the UTXO however and wherever they want, to efficiently replace an old state root with a new one to represent all off-chain balance changes. A new opcode in addition to OP_CAT, such as OP_ZKVERIFY, would be needed to do this in a trustless manner.
This wouldn’t be the end of the world without OP_ZKVERIFY though. The entity updating the merkle root for off-chain transfers could be an n-of-n multisig, with 100% of the participants required to sign off on any root changes. This boils down to the same trust model as BitVM based pegs, where as long as a single honest participant exists, no one’s funds can be stolen. It is a stark improvement over existing BitVM designs however when it comes to the withdrawal process.
In BitVM pegs, users do not have a unilateral withdrawal mechanism. Peg operators must be trusted to fulfill user withdrawals, knowing that they can claim back funds they have spent doing so relatively trustlessly from the BitVM peg. While the incentives of this are very solid, it still does require users essentially getting permission from someone else to exit the system, they cannot do it on their own. With CatVM, users can claim back their funds unilaterally, and an operator is not required to front their own liquidity to process withdrawals.
Wrapping Up
Overall, the design is incomplete in terms of construction. This is not something I would call a Layer 2 in and of itself. It is the core of one, the mechanism and structure for how funds are locked into a Layer 2, and the process for how users can withdraw their funds. It definitely has a lot of flexibility and usefulness to it.
In the worst case scenario, users do not need anyone’s permission to safely claim their funds back on-chain. It also allows more flexible programmability of funds, while still carrying the enforcement of those conditions to the base layer in the event of worst case unilateral exits. If one day we do eventually get something like OP_ZKVERIFY, the off-chain state progression can become an actually trustless process.
I don’t expect any concrete demos in the near future, but it definitely is a sound idea in my opinion, and something worth considering. It also shows that the wizards are doing a little more than just pumping stupid jpegs.
A breakdown of Taproot Wizard’s recent CatVM proposal, what it actually is, and what it could be useful for.
Crypto News
BitVM Just Got A Massive Upgrade

The introduction of BitVM smart contracts has marked a significant milestone in the path for scalability and programmability of Bitcoin. Rooted in the original BitVM protocol, Bitlayer’s Finality Bridge introduces the first version of the protocol live on testnet, which is a good starting point for realizing the promises of the Bitcoin Renaissance or “Season 2”.
Unlike earlier BTC bridges that often required reliance on centralized entities or questionable trust assumptions, the Finality Bridge leverages a blend of BitVM smart contracts, fraud proofs, and zero-knowledge proofs. This combination not only enhances security but also significantly reduces the need for trust in third parties. We’re not at the trustless level that Lightning provides, but this is a million times better than current sidechains designs claiming to be Bitcoin Layers 2s (in addition to significantly increasing the design space for Bitcoin applications).
The system operates on a principle where funds are securely locked in addresses governed by a BitVM smart contract, functioning under the premise that at least one participant in the system will act honestly. This setup inherently reduces the trust requirements but has to introduce additional complexities that Bitlayer aims to manage with this version of the bridge.
The Mechanics of Trust
In practical terms, when Bitcoin is locked into the BitVM smart contract through the Finality Bridge, users are issued YBTC – a token that maintains a strict 1:1 peg with Bitcoin. This peg is not just a promise but is enforced by the underlying smart contract logic, ensuring that each YBTC represents a real, locked Bitcoin on the main chain (no fake “restacked” BTC metrics). This mechanism allows users to participate in DeFi activities like lending, borrowing, and yield farming within the Bitlayer ecosystem without compromising on the security and settlement assurances that Bitcoin provides.
While some in the community might find these activities objectionable, this type of architecture allows users to get some guarantees that they previously could not hope to get with traditional sidechain designs, with the added bonus that we do not need to “change” Bitcoin to make it happen (although covenants would make this bridge design completely “trust-minimized, which would effectively make it a “True” Bitcoin Layer 2). For more details about the different levels of risks associated with sidechains designs, take a look at Bitcoin Layers assessment of Bitlayer here.
However, until such advancements come to fruition, the Bitlayer Finality Bridge serves as the best realization of the BitVM 2 paradigm. It’s a testament to what’s possible after the dev “brain drain” from centralized chains back to Bitcoin. Despite all the challenges that BitVM chains will face, I remain exceptionally excited at the prospect of Bitcoin fulfilling its destiny as the Ultimate Settlement Chain for all economic activity.
This article is a Take. Opinions expressed are entirely the author’s and do not necessarily reflect those of BTC Inc or Bitcoin Magazine.
Guillaume’s articles in particular may discuss topics or companies that are part of his firm’s investment portfolio (UTXO Management). The views expressed are solely his own and do not represent the opinions of his employer or its affiliates. He’s receiving no financial compensation for these Takes. Readers should not consider this content as financial advice or an endorsement of any particular company or investment. Always do your own research before making financial decisions.
The BitLayer Finality Bridge is Delivering On The Promises of BitVM – While still far from a fully trustless system, the progress made over the past year is remarkable
Crypto News
Bitcoin Banks: We Should Build Them Ourselves

Bitcoin banks are going to happen. We already have a few of them. We’re going to have more of them. Existing legacy banks are going to start offering services. New banks are going to be founded around Bitcoin. This is completely unavoidable at this point. Bitcoin doesn’t scale. Even absent that, people value other services that inherently require other parties. Debt being the chief one.
This is an inescapable reality.
Even if we could snap our fingers and roll out every well specified opcode and covenant proposal at once, it would still take a lot of time to begin building out self-custodial layers that could compete with something like credit unions and banks offering bitcoin accounts at scale. That is not a problem that can be trivially solved overnight.
So what can we do? We need to embrace a localist attitude around making interaction with your bitcoin easy. This requires a two pronged approach, one involving technical development and the other involving, I hate to say it, lobbying.
There already exist pieces of software like LNDHub or LNBits that allow people to offer custodial accounts for Lightning. We need a lot more software like this, and we need it to be miles better. It needs to not involve tinkering around on the command line and hooking up independent software, or perusing Github to follow manual installation instructions, or fumbling around trying to fix dependencies mismatches.
It needs to just work.
Click, sync to the network, done. It needs to be something that power users who are still not very tech savvy can run safely, and not lose other people’s money. It needs to support more than basic accounts for Lightning. Ecash offers privacy, which would be something important when it comes to small groups of people who know each other. You don’t want your friend seeing what you spend your money on. It needs to support things like Unchained or Nunchuck style on-chain self custody. People aren’t going to want to hold all their friends and family’s life savings, but holding a recovery key to safeguard them from their own mistakes is another matter.
We need the software that will actually scale this type of user interaction beyond a bunch of activist nerds online.
We also need a regulatory carve out. There needs to be a clear acknowledgement that running this type of software for friends and family with trivial amounts of money, say thousands of dollars, and without charging anything for it, is an unregulated activity. Helping friends and family interact with Bitcoin safely and easily, and for free, does not make you a bank. The idea of a few thousand dollars needing to comply with the regulations banks managing billions of dollars do is frankly absurd.
This is the path forward given the current constraints of Bitcoin, and the reality of growing and accelerating adoption, that leads us away from a system that eventually becomes completely captured and neutered by legacy financial institutions.
Instead of depending on them to deal with the current scaling limitations of Bitcoin, we depend on each other.
This article is a Take. Opinions expressed are entirely the author’s and do not necessarily reflect those of BTC Inc or Bitcoin Magazine.
Bitcoiners shouldn’t sit around and wait for fiat banks and financial companies to offer services built on Bitcoin, we should do it ourselves.
Crypto News
Galoy Launches Bitcoin-Backed Loan Software, Sets Groundwork For Open-Source Banking

Founder: Nicolas Burtey
Date Founded: September 2019
Location of Headquarters: United States
Number of Employees: 11
Website: https://www.galoy.io/
Public or Private? Private
Last week, Galoy launched Lana, software that enables banks to accept bitcoin as collateral for loans.
Lana helps community and challenger banks (the banks with which Galoy is looking to work) to offer bitcoin-backed loans to various types of customers.
“Some banks might want to use it to sell to retail, and some might want to use it to sell commercial customers or high-net-worth individuals,” Burtey told Bitcoin Magazine.
In offering such loans to a wide array of customers, Burtey believes that the high cost of borrowing currently associated with such products will come down.
“Today’s interest rates are 12% to 15% if you want to get a loan using your bitcoin as collateral,” said Burtey.
“The rates are high because there are so few financial institutions offering this type of product. We see an opportunity now that the regulations are allowing banks to do things with bitcoin,” he added.
“We think a lot of banks will want to enter this market.”
If Burtey is correct in his prediction that banks are keen to offer bitcoin-backed loans, this will not only lower rates for such loans, but it will also introduce open-source Bitcoin software into the world of banking, which could initiate a new trend in the industry.
But more on that in just a minute. First, some background on Galoy.
Galoy’s History: From Blink Wallet To Lana
Founded in September 2019, Galoy had intentions to enable banks to use bitcoin from the start, but it had to hold off on doing so due to an unfriendly regulatory environment.
So, instead, it focused its efforts on creating and supporting Blink wallet (which was originally called the Bitcoin Beach wallet and which Galoy recently sold), a custodial Bitcoin and Lightning wallet predominantly used at first in El Salvador and then in Bitcoin circular economies globally.
“Galoy’s mission was to onboard banks to Bitcoin five years ago,” said Burtey.
“But the regulatory environment was so bad during the last five years that we decided to create Blink. The reason we are now focusing on our original mission is because with the end of Choke Point 2.0 and the repeal of SAB 121, we think now is the perfect time to help banks adopt Bitcoin.”
Burtey spoke about his work in creating and growing Blink fondly and shared that he had to stop working on the project only because it would be too difficult to continue managing it while also aiming to serve a new type of clientele.
“Blink is a B2C (Business-To-Customer) play, and it’s hard as an early-stage startup to focus on too many things,” explained Burtey.
“Galoy is a B2B (Business-To-Business)-driven business, and we want to work with banks and financial institutions,” he added.
“It’s good to be focused on just one thing.”
And, as mentioned, that one thing will now be Lana.
How Lana Works
Lana is software that Galoy helps banks integrate and manage for a subscription fee. With this software, banks can issue bitcoin-backed loans under the terms they create.
“We’re not the ones deciding how much interest will be charged or anything like that,” explained Burtey.
“We give banks the platform to do this, and then they can figure out their cost of capital, the duration of the loan, the liquidation price for the bitcoin in the loan and the rate at which they want to lend,” he added.
“We’re giving you software, and helping you run and automate that software.”
Something else that Galoy doesn’t do for banks is custody the bitcoin provided as collateral for the loans they issue. Each of the banks with whom the company works is responsible for selecting their own custodian.
“You can go to BitGo or Fireblocks or each loan can have its own multisig,” said Burtey. “We’re agnostic on custody.”
With that said, Lana helps banks monitor the bitcoin in custody so that banks can be aware of whether or not collateral is nearing liquidation levels.
“A key piece of this product is risk management,” said Burtey.
“Bitcoin is volatile, and the bank will need a tool to show that it’s taking calculated risk. So, we’ll provide banks with a dashboard to monitor this risk,” he added.
Who Will Use Lana?
Galoy is targeting community banks and other smaller financial institutions with this new product mostly because they think these smaller players will benefit most from it — and because the big banks likely won’t need such a product.
“We don’t think JP Morgan will really want to work with us,” said Burtey. “They’re probably building something like this themselves, whereas a smaller bank, a credit union or small company probably isn’t.”
Burtey also understands that smaller lenders’ incorporating Lana as opposed to building something comparable themselves can save these financial institutions a significant amount of time and effort.
“Our goal is to say, ‘Look, you can develop this internally, and it will take you six months, a year or longer depending on how much you know about Bitcoin,’” said Burtey. “‘Or we have a lending product as a service for you, and you can launch it much more quickly.’”
And as Burtey and his team onboard their first round of smaller banks, they’ll not only be making history in enabling more banks to accept bitcoin as collateral for loans, but they’ll potentially be altering the trajectory of banking in general by introducing open-source software to it.
Open-Source Bitcoin Banking
Burtey’s long-term vision for Galoy is to do much more than just help banks issue bitcoin-backed loans. He’s looking to introduce open-source software into banking as more banks begin to embrace Bitcoin.
However, it’s important to note that Lana isn’t open-source just yet. It’s fair-source software, and, under such a license, code becomes open-source after two years.
“It’s a delayed open-source system, but it’s all available on GitHub,” said Burtey. “You can go and try it, test it, and play with it on your own.
Under the fair-source license, no company other than Galoy can sell the product to a bank right now, allowing Galoy to profit while still building with auditable code.
“We sell the deployment, and we help banks to plug in to their custodian,” explained Burtey. “We’re building in the open — but we also want to generate revenue.”
Beyond helping banks implement Lana, Burtey’s wants to develop open-source “core banking software,” as he’s looking to disrupt the “core ledger” oligopoly.
“The core ledger is where banks store the account data, customer information and transaction details,” said Burtey. “It’s the source of truth for banks.”
And only three companies — FIS, Fiserv and Jack Henry — have the core ledger market cornered.
“These are all like hundred billion dollar companies that you’ve probably never heard about because all they do is focus on selling software to banks,” said Burtey.
“Our long-term goal is to disrupt this industry by making something that is open source,” said Burtey. “Today, there is no company that does core banking with the idea of open source, and so we’re working towards this.”
Burtey envisions a world in which open-source software can make it much easier for someone to start a Bitcoin bank. (For those who wince at the words “Bitcoin” and “bank” being used in tandem, might I remind you that it was the legendary Hal Finney himself who wrote that bitcoin-backed banks would serve as a scaling solution.)
“To start a bank today is a very expensive and complicated process,” said Burtey. “You have to pay $100,000 plus just to purchase the core ledger technology.”
Burtey then referenced his own experience in starting Blink wallet, essentially a bitcoin bank run on open-source code, before continuing.
“I just went to El Salvador and started what was effectively my own bank because I wanted to,” said Burtey.
“We need to reinvent how core banking software is being made in the world of Bitcoin, and I think this is where open-source becomes relevant,” he added.
“This is really why I think the world of banking and Bitcoin will be very different from the world of banking with fiat, and I think we’re one of the companies at the forefront of this.”
Galoy founder and CEO Nicolas Burtey wants to help more borrowers use bitcoin as collateral for loans while introducing open-source software into the traditional banking stack.
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