Crypto News
Why Bitcoin Wallets Need Block Filters

With the advent of software development kits like BDK and LDK, building a bitcoin wallet has never been easier. However, as much as easier development is necessary, it’s important to build in a way that protects user security and privacy by default. For example, how a light wallet connects to a third-party server to receive and send transaction data is an important issue to address.
I believe that bitcoin wallets need block filters to respect a user’s privacy. Why? It’s the only way to keep data from leaking to the server, which would allow it to link a user’s transaction data beyond what is publicly available.
In this article, we will explore why bitcoin wallets need block filters by first looking at how many bitcoin users run full nodes, how API wallets offer good user experience but ultimately lead to all your transactions being linked together, how bloom filters have failed to protect privacy, how block filters are the only lightweight wallet network privacy solution, and finally how this can all be implemented using Tor-only communication to also protect a user’s IP address.
Only a Few Users Run Full Nodes
Running and using a Bitcoin node is the best thing you can do because you’re part of the network and you don’t need any intermediaries to receive and broadcast transaction data. However, It’s obvious that running a full node is not for everyone; the existence and need for light clients (Simple Payment Verification) was even envisioned by Satoshi in the Bitcoin whitepaper.
We can’t know how many users are running a full node, we can only know how many nodes there are. Conservative estimates that count only listening nodes would put this number at around 16,000, as seen on the Bitnodes.io site. More accurate estimates that count both listening and non-listening nodes such as Luke Dashjr’s node count tool put this number higher, at around 53,000.
It’s also important to be aware of the historical context of the number of full bitcoin nodes. According to the Bitcoin Node Count History by Luke Dashjr, we can observe that the usage of bitcoin nodes is far from its peak. On January 13, 2018, the count reached 205,000. This was highly related to the fact that bitcoin had reached its previous all-time high a few weeks earlier. In 2021, we can observe that the node count also increased when the price went up, but it only reached close to 90,000.
We can confirm that there are few users running bitcoin nodes, and that this number is not increasing over time. Light wallets are much easier to use than a bitcoin node, and we need to find the right network privacy solution to implement. Let’s take a look at the most used technology today, which is API wallets.
API Wallet Service Providers Collect Your Data by Default
Most bitcoin wallets use APIs (Application Specific Interface) to send and receive user transaction data. This technology is highly scalable and provides the best user experience, as requests are instantaneous. However, it has an inherent privacy caveat. Let’s break down how it works and how service providers collect your data by default.
When you initialize a standard bitcoin wallet, you import or create a mnemonic seed phrase and set the desired derivation path (often automatically). This gives you a master public key, often called an xpub. Here’s what it looks like:
xpub6CUGRUonZSQ4TWtTMmzXdrXDtypWKiKrhko4egpiMZbpiaQL2jkwSB1icqYh2cfDfVxdx4df189oLKnC5fSwqPfgyP3hooxujYzAu3fDVmz
Once that’s done, the xpub is automatically sent to the service provider’s server, where it derives bitcoin addresses within the gap limit (how many unused addresses with a balance of zero will be checked before the server stops scanning for funds). These addresses are looked up in the server’s index, and if transactions are found, they are sent to the user’s client. The addresses are watched in case new transactions occur. In addition, when a user sends a transaction, it’s also sent through the same communication channel.
It’s obvious that this process is very efficient and allows API wallets to provide a fast and easy user experience. However, the service provider will be able to link all of our transactions together, and thus collect your private information by default. Fortunately, many API wallets allow users to connect through Tor, so at least a user’s IP address is protected.
Let’s now examine an alternative method that does not depend on a single server, the use of bloom filters on light wallets.
Why Bloom Filters Don’t Work for Privacy
Some wallets allow a user to receive and send transaction data through Bloom filters. This communication method was introduced in BIP37 and was originally thought to be private. In this section, we’ll break down what Bloom filters are and why they’re actually not good for privacy.
Bloom filters are probabilistic data structures used to test whether an element is a member of a set. In the bitcoin context, bloom filters are created by a light client and sent to network peers, which test whether there’s a match between an address (element) and blockchain data (set). If there’s a match, the transaction data is sent to the light client. It’s probabilistic because there are false positives, but these are later discarded by the light client.
It was thought that the false positive rate would be high enough that a network peer wouldn’t be able to tell which transactions were really yours and which were fake. However, due to an implementation error, the false positive rate was actually reduced.
Additionally, a light client can create different bloom filters for the same wallet, and if two or more are collected by a network peer, the intersection can be calculated to remove false positives. Finally, if blockchain data is analyzed and the user doesn’t coinjoin or use coin control, a network peer can infer which addresses don’t belong to the user.
You can read more about the privacy issues with BIP37 here. Now let’s examine the remaining light client network solution.
A Bitcoin Wallet Needs Block Filters for Privacy
Back in 2018, there was no real solution to this problem, block filters weren’t a thing yet. Fortunately, they were introduced the following year in BIP157 and 158, and are now implemented in several wallets and bitcoin software such as Wasabi, Blixt, Breez, LND, and LDK. They’re often referred to as Neutrino. In this section, we’ll examine how they work and why they’re the right solution for network privacy.
Block filters compress block data to help wallets receive transactions from peers without compromising privacy by downloading specific blocks instead of looking up individual transactions.
The block filter process typically involves three steps. First, a user downloads the block filters representing the blockchain from a network peer in the case of Breez, or from the coordinator server in the case of Wasabi. Then, the light client checks to see if the addresses within the gap limit match a block filter. Finally, if there’s a match, the corresponding block is downloaded.
Because we’re downloading entire blocks instead of individual transactions, and because there’s a false positive rate, the block filter method works to protect a user’s privacy from network peers. Unlike Bloom filters and API wallets, it can’t figure out (or doesn’t collect directly) the connection between a user’s transactions, other than what is publicly known on the blockchain.
Block filters are part of the solution to network privacy, but something else is needed to complete the picture.
Tor is the Last Remaining Piece to Solving Network Privacy
Tor and bitcoin go hand in hand, and together with block filters, can solve network privacy for lightweight clients. Tor hides a user’s IP address from the destination server by routing it through a network of nodes. This mechanism is called onion routing because of the multiple layers of communication.
Tor and block filtering have one thing in common. They’re both processes that can slow down performance, and that can be noticeable and degrade the user experience. Some people think you just have to accept this, but I think it can be improved to the point where it’s barely noticeable.
For example, the Tor community has implemented a communication reliability solution called Conflux. Instead of making a single request, clients make two requests using two different Tor circuits to increase the likelihood of fast completion. This, along with innovations in wallet loading for block filters like Turbosync on the Wasabi wallet, will lead us to a future where a user doesn’t have to choose between usability and privacy, but can enjoy both.
This is a guest post by Gustavo Flores Echaiz. Opinions expressed are entirely their own and do not necessarily reflect those of BTC Inc or Bitcoin Magazine.
Most Bitcoin wallets leak your private information to the wallet provider, block filters can help fix that.
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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