Noir
22 Mar
## min read

Zero-knowledge gaming with BattleZips x Noir

BattleZips and Noir partnered up for zero-knowledge gaming, showcasing encrypted gameplay on the blockchain.

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Building games of imperfect information with Aztec’s Noir language

Noir was conceived of as an open-source, universal zero knowledge language. It was always meant to make the experience of developing in zero-knowledge much more accessible, by:

  • having simple to read syntax that’s easy to reason about
  • abstracting away cryptographic concepts and security considerations
  • incorporating cryptographic libraries for commonly used crypto primitives

So when we heard about the Mach34 team and their work on BattleZips — a Battleship clone relying on zero-knowledge — we knew we had to work together.We met the Mach34 team after they placed at the ETHDenver 2022 hackathon with a Circom-written version of the classic Hasbro game Battleship.Shortly after we released Noir, they expressed ➡️ interest in rewriting Battlezips, providing us feedback, and creating a tutorial series on writing zk circuits and programs in Noir.

➡️ Watch the BattleZips-Noir YouTube series here.

We provided them an Aztec Grant in late 2022, and they were off to the races, culminating in showcasing the Noir-powered Battlezips running in the browser at our sponsored game night at ETHDenver 2023.

➡️ Play Battlezips in your browser.

Here’s an unabridged conversation with Mach34 on their experience building on Noir and what developers can expect building on the universal zk language.

A Noir-ish conversation with Mach34

Q: Tell us about BattleZips. How does the game use zero-knowledge cryptography?

A: BattleZips is a zero-knowledge implementation of the popular board game Battleship that uses proofs to shield ship positions. While this is by no means an original idea for a zero-knowledge application, Battleships was chosen as it is a simple but complete example of integrating arbitrary business logic in zero knowledge circuits.

By settling zero knowledge proofs in smart contracts, we can create novel digital and economic interactions that make the existing role of Information Escrow by third parties obsolete. BattleZips helped us understand how to apply zero knowledge proofs, and we hope the BattleZips-Noir course gives you the same advantages!

Q: What inspired you to start Mach 34 and develop BattleZips? Why explore Noir?

A: BattleZips marked the beginning of our journey into zero-knowledge cryptography and expanded our horizon on where this technology could be applied in real world use cases.

This is one of the factors that lead us to creating Mach 34. Mach 34 is a Web3 and ZK Software Consultancy. We chose to focus on mastering the web3 tech stack for the sake of expertise rather than a specific application. This enables us to explore any industry ripe for decentralization, growing our overall experience with the enterprise of web3.

Corporations and governments alike habitually abuse the authoritative topology of web2 networks; as Web3/ ZK Consultants, we have the means and the desire to help innovators usurp centralized processes and give sovereignty in cyberspace back to the users.

It is crucial that we stay up to date with the latest trends in this fast developing space to ensure we provide superior expertise to clients. Our prior experience writing proofs demonstrated to us that there is a significant variation between the different tools that exist, how rapidly they can be applied to an engineering problem, and what they accomplish. This led us to explore Noir upon its official release and see how it differentiated itself from pre-existing alternatives.

Q: How did you find the ease of usability of Noir compared to other zero-knowledge domain specific languages you’ve worked with?

A: Prior to Noir we used the Circom language and the Halo 2 proving system written in Rust. Proceeding from a first look at the Noir documentation to writing circuits was a fairly quick and straightforward process.

We thought that Noir lived up to most of what it promised in its introductory medium post. If one were to begin learning Noir without wanting to get bogged down in learning the inner workings of ZK and how circuits translate to proofs then they could certainly do so. It does a good job of abstracting away from the more complex aspects of the topic.

One thing that could improve the developer experience is ensuring that the nargo command-line tool and the Aztec NPM packages compile the same Noir version. This is an issue we ran into mid way through the development process that resulted in a refactor to ensure we could test our circuits with the Aztec NPM packages.

Q: As a full-stack development shop, how has the process of incorporating zk-cryptography changed the way you approach software development projects?

A: Our interest in zero-knowledge cryptography was one of the driving factors for starting Mach 34. Historically and to this day, one of the most sought after skills in the web3 space is the ability to write smart contracts.

Similarly as the past few years have shown, we believe enabling privacy and scalability in web3 applications is only going to become more and sought after and ultimately a necessity. In anticipation of this we have positioned ourselves at Mach 34 to have the skills and expertise necessary to help companies engineer ZK solutions.

Q: What kind of impact do you think Noir and other zero-knowledge domain specific languages will have on the broader software development community? Where do you see the industry going?

A: Noir and other ZK DSLs play a pivotal role in the proliferation of zero-knowledge cryptography by abstracting away from the underlying cryptographic principles.

As history shows, abstraction is absolutely necessary for any technology to become widely adopted. If engineers were never able to design high level programming languages from low-level opcodes then we would have far fewer and less effective software developers than we do today.

Once the complexity and thought is removed from the underlying components that make zero-knowledge cryptography possible in the first place, engineers have more time to think about applications that would benefit from ZK. It looks like we are about to enter an exciting phase where we will start to see more examples of the technology applied to real world use cases.

Q: What advice would you give to developers who are interested in learning more about zero-knowledge cryptography and how to use it in their projects?

A: This is definitely an exciting space to get involved in given it is still very much in its infancy. It is poised to solve issues related to privacy and scalability in public blockchains, as well as contexts out of web3 where there is currently a lack of much needed privacy.

This being said, resources for learning are still sparse and those that exist often have a technical complexity that can make them hard to digest. It can take quite a bit of patience and perseverance to become acclimated to this space but it is well worth the effort given that you are one of the individuals pioneering the ecosystem.

If you are a developer that has an interest in getting started in ZK then I think reading some high-level introductory materials would be a good starting point.

After a basic understanding is gained on the topic then exploring a DSL like Circom or Noir to write a simple circuit would be a beneficial next step.

Once it becomes clearer to you what can be accomplished and what tools are at your disposal then really the limit is what you can ideate. The cool thing is that there is still so much room for novel innovation that it could very well be the case no one has thought of your idea yet. Don’t sit idle and wait for things to develop further! Now is a great time to jump in!

Q: Are there any upcoming projects at Mach 34 that you can share with us that utilize zero-knowledge cryptography or other cutting-edge technologies?

A: Mach 34 has been researching and working towards constructing a “Zero-Knowledge State Channel”. While rollups offer fantastic scalability, we were put off by the need for a sequencer. Furthermore, aside from Aztec Connect and a few others, ZK Rollups do not have any private state. Thus, we began to explore how state channels might be repurposed with zero knowledge.

To open a ZK State Channel, parties will agree on the terms of the execution (like a smart contract). The channel initialization dictates what steps can be taken next, and by whom. Rather than posting every transaction on-chain, a state object is recursively built off-chain.

While previous state channel constructions had optimistic trust assumptions, we can leverage ZK to perform verifiable computations that have instant, trustless finality. Once a state channel has reached an end condition, the entire state execution is notarized by posting the state channel proof on-chain for all nodes to verify in zero knowledge.

This final proof further employs zero knowledge to hide most of the intermediate state; only pre-determined derived metrics or public outputs are made publicly available on-chain.

This has many interesting use-cases; we plan to demonstrate how this construction is useful for credit scoring by adding ELO scores to the State Channel version of BattleZips. This provides a verifiable metric that scores the performance of an individual without revealing any of their in-game moves.

We envision countless use-cases for ZK State Channels across all segments of web3. Undoubtedly, there are use-cases that we haven’t thought of. For this reason, all of our work on ZK State Channels is free and open source. While we intend to utilize the infrastructure for profit, we want to make sure that all possibilities are explored in service of the best possible future for web3 developers and users.

Q: What are some use cases you’re excited for?

A: One area of exciting potential outside of blockchain is how zero-knowledge can transform personal identification.

When providing personal ID, the majority of the time more information is conveyed than necessary. Proving one is of a legal drinking age need only confirm the person is above 21 years of age, yet sharing the ID divulges information such as street address and name.

Using zero knowledge proofs conceivably one could prove they are at least 21 without having to provide additional information. Another example is having to provide a social security number in a KYC process. Leaking a SSN number can have catastrophic consequences so one would prefer this is done as infrequently as possible. With ZK proofs instead one could prove they bear a SSN number without needing to reveal exactly what theirs is.

Explore the BattleZips project

We’re thrilled that the Mach34 team have done such a deep and candid dive into Noir’s capabilities, and their feedback has been invaluable.For developers interested in building on Noir, check out their well-documented BattleZips repo.

➡️ Explore the BattleZips Github repo and codebase.

Build on Noir

Interested in building zero-knowledge applications on Noir — or contributing to the open-source project?

Join Us

We’re always looking for talented engineers, cryptographers, and businesspeople to join Aztec. We are committed to bringing encryption to blockchain through our encrypted zkRollup, and we’ve raised over $125 million from the best investors in crypto, including a16z and Paradigm to do so. Come onboard.

➡️ See our open roles here.

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Aztec Network
Aztec Network
8 Oct
xx min read

Aztec: The Private World Computer

Privacy has emerged as a major driver for the crypto industry in 2025. We’ve seen the explosion of Zcash, the Ethereum Foundation’s refocusing of PSE, and the launch of Aztec’s testnet with over 24,000 validators powering the network. Many apps have also emerged to bring private transactions to Ethereum and Solana in various ways, and exciting technologies like ZKPassport that privately bring identity on-chain using Noir have become some of the most talked about developments for ushering in the next big movements to the space. 

Underpinning all of these developments is the emerging consensus that without privacy, blockchains will struggle to gain real-world adoption. 

Without privacy, institutions can’t bring assets on-chain in a compliant way or conduct complex swaps and trades without revealing their strategies. Without privacy, DeFi remains dominated and controlled by advanced traders who can see all upcoming transactions and manipulate the market. Without privacy, regular people will not want to move their lives on-chain for the entire world to see every detail about their every move. 

While there's been lots of talk about privacy, few can define it. In this piece we’ll outline the three pillars of privacy and gives you a framework for evaluating the privacy claims of any project. 

The Three Pillars of Privacy 

True privacy rests on three essential pillars: transaction privacy, identity privacy, and computational privacy. It is only when we have all three pillars that we see the emergence of a private world computer. 

Transaction: What is being sent?

Transaction privacy means that both inputs and outputs are not viewable by anyone other than the intended participants. Inputs include any asset, value, message, or function calldata that is being sent. Outputs include any state changes or transaction effects, or any transaction metadata caused by the transaction. Transaction privacy is often primarily achieved using a UTXO model (like Zcash or Aztec’s private state tree). If a project has only the option for this pillar, it can be said to be confidential, but not private. 

Identity: Who is involved?

Identity privacy means that the identities of those involved are not viewable by anyone other than the intended participants. This includes addresses or accounts and any information about the identity of the participants, such as tx.origin, msg.sender, or linking one’s private account to public accounts. Identity privacy can be achieved in several ways, including client-side proof generation that keeps all user info on the users’ devices. If a project has only the option for this pillar, it can be said to be anonymous, but not private. 

Computation: What happened? 

Computation privacy means that any activity that happens is not viewable by anyone other than the intended participants. This includes the contract code itself, function execution, contract address, and full callstack privacy. Additionally, any metadata generated by the transaction is able to be appropriately obfuscated (such as transaction effects, events are appropriately padded, inclusion block number are in appropriate sets). Callstack privacy includes which contracts you call, what functions in those contracts you’ve called, what the results of those functions were, any subsequent functions that will be called after, and what the inputs to the function were. A project must have the option for this pillar to do anything privately other than basic transactions. 

From private money to a private world computer 

Bitcoin ushered in a new paradigm of digital money. As a permissionless, peer-to-peer currency and store of value, it changed the way value could be sent around the world and who could participate. Ethereum expanded this vision to bring us the world computer, a decentralized, general-purpose blockchain with programmable smart contracts. 

Given the limitations of running a transparent blockchain that exposes all user activity, accounts, and assets, it was clear that adding the option to preserve privacy would unlock many benefits (and more closely resemble real cash). But this was a very challenging problem. Zcash was one of the first to extend Bitcoin’s functionality with optional privacy, unlocking a new privacy-preserving UTXO model for transacting privately. As we’ll see below, many of the current privacy-focused projects are working on similar kinds of private digital money for Ethereum or other chains. 

Now, Aztec is bringing us the final missing piece: a private world computer.

A private world computer is fully decentralized, programmable, and permissionless like Ethereum and has optional privacy at every level. In other words, Aztec is extending all the functionality of Ethereum with optional transaction, identity, and computational privacy. This is the only approach that enables fully compliant, decentralized applications to be built that preserve user privacy, a new design space that we see as ushering in the next Renaissance for the space. 

Where are we now? 

Private digital money

Private digital money emerges when you have the first two privacy pillars covered - transactions and identity - but you don’t have the third - computation. Almost all projects today that claim some level of privacy are working on private digital money. This includes everything from privacy pools on Ethereum and L2s to newly emerging payment L1s like Tempo and Arc that are developing various degrees of transaction privacy 

When it comes to digital money, privacy exists on a spectrum. If your identity is hidden but your transactions are visible, that's what we call anonymous. If your transactions are hidden but your identity is known, that's confidential. And when both your identity and transactions are protected, that's true privacy. Projects are working on many different approaches to implement this, from PSE to Payy using Noir, the zkDSL built to make it intuitive to build zk applications using familiar Rust-like syntax. 

The Private World Computer 

Private digital money is designed to make payments private, but any interaction with more complex smart contracts than a straightforward payment transaction is fully exposed. 

What if we also want to build decentralized private apps using smart contracts (usually multiple that talk to each other)? For this, you need all three privacy pillars: transaction, identity, and compute. 

If you have these three pillars covered and you have decentralization, you have built a private world computer. Without decentralization, you are vulnerable to censorship, privileged backdoors and inevitable centralized control that can compromise privacy guarantees. 

Aztec: the Private World Computer 

What exactly is a private world computer? A private world computer extends all the functionality of Ethereum with optional privacy at every level, so developers can easily control which aspects they want public or private and users can selectively disclose information. With Aztec, developers can build apps with optional transaction, identity, and compute privacy on a fully decentralized network. Below, we’ll break down the main components of a private world computer.

Private Smart Contracts 

A private world computer is powered by private smart contracts. Private smart contracts have fully optional privacy and also enable seamless public and private function interaction. 

Private smart contracts simply extend the functionality of regular smart contracts with added privacy. 

As a developer, you can easily designate which functions you want to keep private and which you want to make public. For example, a voting app might allow users to privately cast votes and publicly display the result. Private smart contracts can also interact privately with other smart contracts, without needing to make it public which contracts have interacted. 

Aztec’s Three Pillars of Privacy

Transaction: Aztec supports the optionality for fully private inputs, including messages, state, and function calldata. Private state is updated via a private UTXO state tree.

Identity: Using client-side proofs and function execution, Aztec can optionally keep all user info private, including tx.origin and msg.sender for transactions. 

Computation: The contract code itself, function execution, and call stack can all be kept private. This includes which contracts you call, what functions in those contracts you’ve called, what the results of those functions were, and what the inputs to the function were. 

Decentralization

A decentralized network must be made up of a permissionless network of operators who run the network and decide on upgrades. Aztec is run by a decentralized network of node operators who propose and attest to transactions. Rollup proofs on Aztec are also run by a decentralized prover network that can permissionlessly submit proofs and participate in block rewards. Finally, the Aztec network is governed by the sequencers, who propose, signal, vote, and execute network upgrades.

What Can You Build with a Private World Computer?

Private DeFi

A private world computer enables the creation of DeFi applications where accounts, transactions, order books, and swaps remain private. Users can protect their trading strategies and positions from public view, preventing front-running and maintaining competitive advantages. Additionally, users can bridge privately into cross-chain DeFi applications, allowing them to participate in DeFi across multiple blockchains while keeping their identity private despite being on an existing transparent blockchain.

Private Dark Pools

This technology makes it possible to bring institutional trading activity on-chain while maintaining the privacy that traditional finance requires. Institutions can privately trade with other institutions globally, without having to touch public markets, enjoying the benefits of blockchain technology such as fast settlement and reduced counterparty risk, without exposing their trading intentions or volumes to the broader market.

Private RWAs & Stablecoins

Organizations can bring client accounts and assets on-chain while maintaining full compliance. This infrastructure protects on-chain asset trading and settlement strategies, ensuring that sophisticated financial operations remain private. A private world computer also supports private stablecoin issuance and redemption, allowing financial institutions to manage digital currency operations without revealing sensitive business information.

Compliant Apps

Users have granular control over their privacy settings, allowing them to fine-tune privacy levels for their on-chain identity according to their specific needs. The system enables selective disclosure of on-chain activity, meaning users can choose to reveal certain transactions or holdings to regulators, auditors, or business partners while keeping other information private, meeting compliance requirements.

Let’s build

The shift from transparent blockchains to privacy-preserving infrastructure is the foundation for bringing the next billion users on-chain. Whether you're a developer building the future of private DeFi, an institution exploring compliant on-chain solutions, or simply someone who believes privacy is a fundamental right, now is the time to get involved.

Follow Aztec on X to stay updated on the latest developments in private smart contracts and decentralized privacy technology. Ready to contribute to the network? Run a node and help power the private world computer. 

The next Renaissance is here, and it’s being powered by the private world computer.

Aztec Network
Aztec Network
24 Sep
xx min read

Testnet Retro - 2.0.3 Network Upgrade

Special thanks to Santiago Palladino, Phil Windle, Alex Gherghisan, and Mitch Tracy for technical updates and review.

On September 17th, 2025, a new network upgrade was deployed, making Aztec more secure and flexible for home stakers. This upgrade, shipped with all the features needed for a fully decentralized network launch, includes a completely redesigned slashing system that allows inactive or malicious operators to be removed, and does not penalize home stakers for short outages. 

With over 23,000 operators running validators across 6 continents (in a variety of conditions), it is critical not to penalize nodes that temporarily drop due to internet connectivity issues. This is because users of the network are also found across the globe, some of whom might have older phones. A significant effort was put into shipping a low-memory proving mode that allows older mobile devices to send transactions and use privacy-preserving apps. 

The network was successfully deployed, and all active validators on the old testnet were added to the queue of the new testnet. This manual migration was only necessary because major upgrades to the governance contracts had gone in since the last testnet was deployed. The new testnet started producing blocks after the queue started to be “flushed,” moving validators into the rollup. Because the network is fully decentralized, the initial flush could have been called by anyone. The network produced ~2k blocks before an invalid block made it to the chain and temporarily stalled block production. Block production is now restored and the network is healthy. This post explains what caused the issue and provides an update on the current status of the network. 

Note: if you are a network operator, you must upgrade to version 2.0.3 and restart your node to participate in the latest testnet. If you want to run a node, it’s easy to get started.

What’s included in the upgrade? 

This upgrade was a team-wide effort that optimized performance and implemented all the mechanisms needed to launch Aztec as a fully decentralized network from day 1. 

Feature highlights include: 

  • Improved node stability: The Aztec node software is now far more stable. Users will see far fewer crashes and increased performance in terms of attestations and blocks produced. This translates into a far better experience using testnet, as transactions get included much faster.
  • Boneh–Lynn–Shacham (BLS) keys: When a validator registers on the rollup, they also provide keys that allow BLS signature aggregation. This unlocks future optimizations where signatures can be combined via p2p communication, then verified on Ethereum, while proving that the signatures come from block proposers.
  • Low-memory proving mode: The client-side proving requirements have dropped dramatically from 3.7GB to 1.3GB through a new low-memory proving mode, enabling older mobile devices to send Aztec transactions and use apps like zkPassport. 
  • AVM performance: The Aztec Virtual Machine (AVM) performance has seen major improvements with constraint coverage jumping from 0% to approximately 90-95%, providing far more secure AVM proving and more realistic proving performance numbers from provers. 
  • Flexible key management: The system now supports flexible key management through keystores, multi-EOA support, and remote signers, eliminating the need to pass private keys through environment variables and representing a significant step toward institutional readiness. 
  • Redesigned slashing: Slashing has been redesigned to provide much better consensus guarantees. Further, the new configuration allows nodes not to penalize home stakers for short outages, such as 20-minute interruptions. 
  • Slashing Vetoer: The Slasher contract now has an explicit vetoer: an address that can prevent slashing. At Mainnet, the initial vetoer will be operated by an independent group of security researchers who will also provide security assessments on upgrades. This acts as a failsafe in the event that nodes are erroneously trying to slash other nodes due to a bug.

With these updates in place, we’re ready to test a feature-complete network. 

What happened after deployment? 

As mentioned above, block production started when someone called the flush function and a minimum number of operators from the queue were let into the validator set. 

Shortly thereafter, while testing the network, a member of the Aztec Labs team spun up a “bad” sequencer that produced an invalid block proposal. Specifically, one of the state trees in the proposal was tampered with. 

Initial block production 

The expectation was that this would be detected immediately and the block rejected. Instead, a bug was discovered in the validator code where the invalid block proposal wasn't checked thoroughly enough. In effect, the proposal got enough attestations, so it was posted to the rollup. Due to extra checks in the nodes, when the nodes pulled the invalid block from Ethereum, they detected the tampered tree and refused to sync it. This is a good outcome as it prevented the attack. Additionally, prover nodes refused to prove the epoch containing the invalid block. This allowed the rollup to prune the entire bad epoch away. After the prune, the invalid state was reset to the last known good block.

Block production stalled

The prune revealed another, smaller bug, where, after a failed block sync, a prune does not get processed correctly, requiring a node restart to clear up. This led to a 90-minute outage from the moment the block proposal was posted until the testnet recovered. The time was equally split between waiting for pruning to happen and for the nodes to restart in order to process the prune.

The Fix

Validators were correctly re-executing all transactions in the block proposals and verifying that the world state root matched the one in the block proposal, but they failed to check that intermediate tree roots, which are included in the proposal and posted to the rollup contract on L1, were also correct. The attack tweaked one of these intermediate roots while proposing a correct world state root, so it went unnoticed by the attestors. 

As mentioned above, even though the block made it through the initial attestation and was posted to L1, the invalid block was caught by the validators, and the entire epoch was never proven as provers refused to generate a proof for the inconsistent state. 

A fix was pushed that resolved this issue and ensured that invalid block proposals would be caught and rejected. A second fix was pushed that ensures inconsistent state is removed from the uncommitted cache of the world state.

Block production restored

What’s Next

Block production is currently running smoothly, and the network health has been restored. 

Operators who had previously upgraded to version 2.0.3 will need to restart their nodes. Any operator who has not upgraded to 2.0.3 should do so immediately. 

Attestation and Block Production rate on the new rollup

Slashing has also been functioning as expected. Below you can see the slashing signals for each round. A single signal can contain votes for multiple validators, but a validator's attester needs to receive 65 votes to be slashed.

Votes on slashing signals

Join us this Thursday, September 25, 2025, at 4 PM CET on the Discord Town Hall to hear more about the 2.0.3 upgrade. To stay up to date with the latest updates for network operators, join the Aztec Discord and follow Aztec on X.

Noir
Noir
18 Sep
xx min read

Just write “if”: Why Payy left Halo2 for Noir

The TL;DR:

Payy, a privacy-focused payment network, just rewrote its entire ZK architecture from Halo2 to Noir while keeping its network live, funds safe, and users happy. 

Code that took months to write now takes weeks (with MVPs built in as little as 30 minutes). Payy’s codebase shrank from thousands of lines to 250, and now their entire engineering team can actually work on its privacy infra. 

This is the story of how they transformed their ZK ecosystem from one bottlenecked by a single developer to a system their entire team can modify and maintain.

Starting with Halo2

Eighteen months ago, Payy faced a deceptively simple requirement: build a privacy-preserving payment network that actually works on phones. That requires client-side proving.

"Anyone who tells you they can give you privacy without the proof being on the phone is lying to you," Calum Moore - Payy's Technical Lead - states bluntly.

To make a private, mobile network work, they needed:

  • Mobile proof generation with sub-second performance
  • Minimal proof sizes for transmission over weak mobile signals
  • Low memory footprint for on-device proving
  • Ethereum verifier for on-chain settlement

To start, the team evaluated available ZK stacks through their zkbench framework:

STARKs (e.g., RISC Zero): Memory requirements made them a non-starter on mobile. Large proof sizes are unsuitable for mobile data transmission.

Circom with Groth16: Required trusted setup ceremonies for each circuit update. It had “abstracted a bit too early” and, as a result, is not high-level enough to develop comfortably, but not low-level enough for controls and optimizations, said Calum.

Halo2: Selected based on existing production deployments (ZCash, Scroll), small proof sizes, and an existing Ethereum verifier. As Calum admitted with the wisdom of hindsight: “Back a year and a half ago, there weren’t any other real options.”

Bus factor = 1 😳

Halo2 delivered on its promises: Payy successfully launched its network. But cracks started showing almost immediately.

First, they had to write their own chips from scratch. Then came the real fun: if statements.

"With Halo2, I'm building a chip, I'm passing this chip in... It's basically a container chip, so you'd set the value to zero or one depending on which way you want it to go. And, you'd zero out the previous value if you didn't want it to make a difference to the calculation," Calum explained, “when I’m writing in Noir, I just write ‘if’. "

With Halo2, writing an if statement (programming 101) required building custom chip infra. 

Binary decomposition, another fundamental operation for rollups, meant more custom chips. The Halo2 implementation quickly grew to thousands of lines of incomprehensible code.

And only Calum could touch any of it.

The Bottleneck

"It became this black box that no one could touch, no one could reason about, no one could verify," he recalls. "Obviously, we had it audited, and we were confident in that. But any changes could only be done by me, could only be verified by me or an auditor."

In engineering terms, this is called a bus factor of one: if Calum got hit by a bus (or took a vacation to Argentina), Payy's entire proving system would be frozen. "Those circuits are open source," Calum notes wryly, "but who's gonna be able to read the Halo2 circuits? Nobody."

Evaluating Noir: One day, in Argentina…

During a launch event in Argentina, "I was like, oh, I'll check out Noir again. See how it's going," Calum remembers. He'd been tracking Noir's progress for months, occasionally testing it out, waiting for it to be reliable.

"I wrote basically our entire client-side proof in about half an hour in Noir. And it probably took me - I don't know, three weeks to write that proof originally in Halo2."

Calum recreated Payy's client-side proof in Noir in 30 minutes. And when he tested the proving speed, without any optimization, they were seeing 2x speed improvements.

"I kind of internally… didn't want to tell my cofounder Sid that I'd already made my decision to move to Noir," Calum admits. "I hadn't broken it to him yet because it's hard to justify rewriting your proof system when you have a deployed network with a bunch of money already on the network and a bunch of users."

Rebuilding (Ship of Theseus-ing) Payy

Convincing a team to rewrite the core of a live financial network takes some evidence. The technical evaluation of Noir revealed improvements across every metric:

Proof Generation Time: Sub-0.5 second proof generation on iPhones. "We're obsessive about performance," Calum notes (they’re confident they can push it even further).

Code Complexity: Their entire ZK implementation compressed from thousands of lines of Halo2 to just 250 lines of Noir code. "With rollups, the logic isn't complex—it's more about the preciseness of the logic," Calum explains.

Composability: In Halo2, proof aggregation required hardwiring specific verifiers for each proof type. Noir offers a general-purpose verifier that accepts any proof of consistent size.

"We can have 100 different proving systems, which are hyper-efficient for the kind of application that we're doing," Calum explains. "Have them all aggregated by the same aggregation proof, and reason about whatever needs to be."

Migration Time

Initially, the goal was to "completely mirror our Halo2 proofs": no new features. This conservative approach meant they could verify correctness while maintaining a live network.

The migration preserved Payy's production architecture:

  • Rust core (According to Calum, "Writing a financial application in JavaScript is borderline irresponsible")
  • Three-proof system: client-side proof plus two aggregators  
  • Sparse Merkle tree with Poseidon hashing for state management

When things are transparent, they’re secure

"If you have your proofs in Noir, any person who understands even a little bit about logic or computers can go in and say, 'okay, I can kinda see what's happening here'," Calum notes.

The audit process completely transformed. With Halo2: "The auditors that are available to audit Halo2 are few and far between."

With Noir: "You could have an auditor that had no Noir experience do at least a 95% job."

Why? Most audit issues are logic errors, not ZK-specific bugs. When auditors can read your code, they find real problems instead of getting lost in implementation details.

Code Comparison

Halo2: Binary decomposition

  • Write a custom chip for binary decomposition
  • Implement constraint system manually
  • Handle grid placement and cell references
  • Manage witness generation separately
  • Debug at the circuit level when something goes wrong

Payy’s previous 383 line implementation of binary decomposition can be viewed here (pkg/zk-circuits/src/chips/binary_decomposition.rs).

Payy’s previous binary decomposition implementation

Meanwhile, binary decomposition is handled in Noir with the following single line.

pub fn to_le_bits<let N: u32>(self: Self) -> [u1; N]

(Source)

What's Next

With Noir's composable proof system, Payy can now build specialized provers for different operations, each optimized for its specific task.

"If statements are horrendous in SNARKs because you pay the cost of the if statement regardless of its run," Calum explains. But with Noir's approach, "you can split your application logic into separate proofs, and run whichever proof is for the specific application you're looking for."

Instead of one monolithic proof trying to handle every case, you can have specialized proofs, each perfect for its purpose.

The Bottom Line

"I fell a little bit in love with Halo2," Calum admits, "maybe it's Stockholm syndrome where you're like, you know, it's a love-hate relationship, and it's really hard. But at the same time, when you get a breakthrough with it, you're like, yes, I feel really good because I'm basically writing assembly-level ZK proofs."

“But now? I just write ‘if’.”

Technical Note: While "migrating from Halo2 to Noir" is shorthand that works for this article, technically Halo2 is an integrated proving system where circuits must be written directly in Rust using its constraint APIs, while Noir is a high-level language that compiles to an intermediate representation and can use various proving backends. Payy specifically moved from writing circuits in Halo2's low-level constraint system to writing them in Noir's high-level language, with Barretenberg (UltraHonk) as their proving backend.

Both tools ultimately enable developers to write circuits and generate proofs, but Noir's modular architecture separates circuit logic from the proving system - which is what made Payy's circuits so much more accessible to their entire team, and now allows them to swap out their proving system with minimal effort as proving systems improve.

Payy's code is open source and available for developers looking to learn from their implementation.

Aztec Network
Aztec Network
4 Sep
xx min read

A New Brand for a New Era of Aztec

After eight years of solving impossible problems, the next renaissance is here. 

We’re at a major inflection point, with both our tech and our builder community going through growth spurts. The purpose of this rebrand is simple: to draw attention to our full-stack privacy-native network and to elevate the rich community of builders who are creating a thriving ecosystem around it. 

For eight years, we’ve been obsessed with solving impossible challenges. We invented new cryptography (Plonk), created an intuitive programming language (Noir), and built the first decentralized network on Ethereum where privacy is native rather than an afterthought. 

It wasn't easy. But now, we're finally bringing that powerful network to life. Testnet is live with thousands of active users and projects that were technically impossible before Aztec.

Our community evolution mirrors our technical progress. What started as an intentionally small, highly engaged group of cracked developers is now welcoming waves of developers eager to build applications that mainstream users actually want and need.

Behind the Brand: A New Mental Model

A brand is more than aesthetics—it's a mental model that makes Aztec's spirit tangible. 

Our Mission: Start a Renaissance

Renaissance means "rebirth"—and that's exactly what happens when developers gain access to privacy-first infrastructure. We're witnessing the emergence of entirely new application categories, business models, and user experiences.

The faces of this renaissance are the builders we serve: the entrepreneurs building privacy-preserving DeFi, the activists building identity systems that protect user privacy, the enterprise architects tokenizing real-world assets, and the game developers creating experiences with hidden information.

Values Driving the Network

This next renaissance isn't just about technology—it's about the ethos behind the build. These aren't just our values. They're the shared DNA of every builder pushing the boundaries of what's possible on Aztec.

Agency: It’s what everyone deserves, and very few truly have: the ability to choose and take action for ourselves. On the Aztec Network, agency is native

Genius: That rare cocktail of existential thirst, extraordinary brilliance, and mind-bending creation. It’s fire that fuels our great leaps forward. 

Integrity: It’s the respect and compassion we show each other. Our commitment to attacking the hardest problems first, and the excellence we demand of any solution. 

Obsession: That highly concentrated insanity, extreme doggedness, and insatiable devotion that makes us tick. We believe in a different future—and we can make it happen, together. 

Visualizing the Next Renaissance

Just as our technology bridges different eras of cryptographic innovation, our new visual identity draws from multiple periods of human creativity and technological advancement. 

The Wordmark: Permissionless Party 

Our new wordmark embodies the diversity of our community and the permissionless nature of our network. Each letter was custom-drawn to reflect different pivotal moments in human communication and technological progress.

  • The A channels the bold architecture of Renaissance calligraphy—when new printing technologies democratized knowledge. 
  • The Z strides confidently into the digital age with clean, screen-optimized serifs. 
  • The T reaches back to antiquity, imagined as carved stone that bridges ancient and modern. 
  • The E embraces the dot-matrix aesthetic of early computing—when machines first began talking to each other. 
  • And the C fuses Renaissance geometric principles with contemporary precision.

Together, these letters tell the story of human innovation: each era building on the last, each breakthrough enabling the next renaissance. And now, we're building the infrastructure for the one that's coming.

The Icon: Layers of the Next Renaissance

We evolved our original icon to reflect this new chapter while honoring our foundation. The layered diamond structure tells the story:

  • Innermost layer: Sensitive data at the core
  • Black privacy layer: The network's native protection
  • Open third layer: Our permissionless builder community
  • Outermost layer: Mainstream adoption and real-world transformation

The architecture echoes a central plaza—the Roman forum, the Greek agora, the English commons, the American town square—places where people gather, exchange ideas, build relationships, and shape culture. It's a fitting symbol for the infrastructure enabling the next leap in human coordination and creativity.

Imagery: Global Genius 

From the Mughal and Edo periods to the Flemish and Italian Renaissance, our brand imagery draws from different cultures and eras of extraordinary human flourishing—periods when science, commerce, culture and technology converged to create unprecedented leaps forward. These visuals reflect both the universal nature of the Renaissance and the global reach of our network. 

But we're not just celebrating the past —we're creating the future: the infrastructure for humanity's next great creative and technological awakening, powered by privacy-native blockchain technology.

You’re Invited 

Join us to ask questions, learn more and dive into the lore.

Join Our Discord Town Hall. September 4th at 8 AM PT, then every Thursday at 7 AM PT. Come hear directly from our team, ask questions, and connect with other builders who are shaping the future of privacy-first applications.

Take your stance on privacy. Visit the privacy glyph generator to create your custom profile pic and build this new world with us.

Stay Connected. Visit the new website and to stay up-to-date on all things Noir and Aztec, make sure you’re following along on X.

The next renaissance is what you build on Aztec—and we can't wait to see what you'll create.