Aztec Network
25 Mar
## min read

Privacy for Pennies: Scaling Aztec’s zkRollup

Learn how how Aztec's ZkRollup achieves scalable blockchain privacy at a minimal cost, enhancing both efficiency and security.

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Written by
Jon Wu
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The economics of our privacy-first Ethereum rollup.

Our goal at Aztec is to make privacy a no-brainer. That’s why our rollup is designed to give you fully private Ethereum transactions at dramatically lower cost than mainnet.

We consider privacy a critical missing component of Ethereum’s scalability roadmap, given that its user functionality is non-economic in nature.

But privacy must also be affordable, and in order to understand how we’ll get to privacy for cheap, we need to do a deeper study of rollup economics.

Background on Ethereum scaling

You might already be familiar with the difference between the two consensus Ethereum scaling solutions: Optimistic Rollups (ORUs) and zkRollups (ZKRs). I’ll let Vitalik explain here.

But in case you want my take, here’s the basic trade-off between Optimistic Rollups and zkRollups:

Optimistic

Optimistic rollup block producers post an Ethereum transaction containing a state root. The ecosystem “optimistically” takes the state of the system to be valid.

During a 7 day challenge period, anyone can prove the invalidity of the state transition by downloading the block of transactions and comparing the previous Merkle root state to the new Merkle root state.

If there is an invalid state transition, they can submit a fraud proof, causing the block producer to be slashed and the blockchain state to be rolled back to its original state.

Note that the cost of executing transactions with an optimistic rollup is very close to free, since it’s essentially the cost of computation as done by a single sequencer (just like, a computer somewhere). However, there is still a variable cost of posting data to Ethereum.

Zero-knowledge

In a zero-knowledge rollup, the rollup incurs a significant fixed cost. Rather than passively awaiting fraud proofs, ZKRs proactively post a succinct zero knowledge proof to Ethereum Layer 1 validating a set of off-chain computations (a “validity proof”).

While the security of off-chain transactions in a zkRollup is unimpeachable due to the deterministic nature of zero knowledge proofs, there must be sufficiently high transaction throughput to amortize the cost of posting the proof to Ethereum.

Tl;dr:

  • Optimistic: no fixed costs, finality delayed by 7 day challenge & withdrawal period; in case of fraud, blockchain state gets rolled back
  • zk: high fixed costs, finality limited by speed of rollup, no challenge or withdrawal period, no possible fraud (caveat: as long as the cryptography works as intended)

Simple rollup math

Aztec, of course is a zero-knowledge rollup. (In fact, it’s a recursive zk-rollup–a zk-zk-rollup, but we’ll get to that).

That means it does incur the fixed cost of posting a SNARK-based proof to Ethereum. But it also means it’s highly scalable.

Scalability

What do we mean by scalability? In a blockchain context, scalability means the marginal cost of transactions goes down with each incremental transaction. The faster the marginal cost falls, the more scalable something is.

In terms of cost, optimistic rollups have no fixed expense, but over a large enough number of transactions, zkRollups quickly overcome their fixed cost disadvantage and win over optimistic roll-ups with superior data compression.

So: zkRollups are more scalable.

Now, if you think about most Layer 1’s, including Ethereum, they’re anti-scalable. The more transactions go through Ethereum, the higher the cost of each marginal transaction.

zkRollups for kids

Here’s a school child’s diagram of the scalability equation for Aztec and other zkRollups:

Must be a really good school if this is what they’re teaching ‘em.

Hopefully this gives you a picture of how Aztec’s path to scaling our own rollup:

  • Reduce the cost of posting a rollup (we control this)
  • Increase the number of transactions per rollup (we mostly control this)
  • Lower the per-transaction cost of posting call data (we don’t control this for Ethereum, but we can select a lower-cost data availability solution)

Let’s tackle these one by one, compare the current system relative to performance a year ago, and discuss what they mean for future network performance.

Cost of posting rollups

In Aztec’s current technological paradigm, an improvement of our proving system called UltraPlonk, the cost of posting a proof to Ethereum is approximately 550,000 gas, ~30% cheaper than it was when zk.money was first launched.

We anticipate this coming down to ~180,000 gas with the advent of our next-generation proving system, [super secret code name redacted].

Transactions per rollup

Our current system was recently upgraded from 112 transactions per rollup at zk.money’s launch to 896 transactions per rollup, an improvement in throughput of 8x.

The way Aztec worked under the hood prior to this most recent upgrade is:

  • A proof is generated client-side in-browser
  • 28 client proofs are then aggregated into an “inner” rollup proof
  • 4 inner rollup proofs are then aggregated into an “outer” rollup proof

That “outer” rollup proof is then verified in what we call the root rollup circuit — the circuit that establishes the validity of all the underlying work that goes into ensuring execution on Aztec happened as expected. Then that final proof gets posted on-chain for posterity.

It’s proofs on proofs on proofs.

For the release of Aztec Connect SDK, we’ve increased the outer rollup’s capacity to 32 inner proofs by optimizing the outer rollup circuit. 28 * 32 = 896. Magic.

That’s why we go through all this headache, writing circuits that can efficiently verify recursive Plonk proofs.

If you’re following so far, the share of rollup costs per transaction fell from:

  • 750k / 112 = 6,700 gas; to
  • 550k / 896 = 614 gas → an 11x improvement!

We think that’s well worth inventing novel forms of cryptography.

Per-txn cost of call data

In addition to the proof, which validates Aztec’s off-chain transactions, Aztec also has to post call data¹ for each transaction, such that anyone can reconstruct the state of Aztec’s rollup and prove the validity of off-chain computation.

Currently, the cost of posting call data to Ethereum is 16 gas per byte. Vitalik has submitted EIP-4488 lowering the cost of call data to 3 gas per byte, while there’s another proposal, confusingly named EIP-4844, which offers a new data format specifically designed to lower the cost to rollups of posting data on Ethereum.

Aztec broadly supports efforts to reduce the cost of data on Ethereum, and we’ll discuss the minutiae of the two EIPs in a separate post.

For now, it’s true for our architecture that scaling costs beyond a few hundred transactions asymptotically approach the cost of call data:

aditi on Twitter: "the result is that even in the case of end users leveraging rollups, posting call data to Eth beholds them to the gas costs they face today as a result of this fixed ratio. modeled below, you'll see that cost will always hit a rough asymptote b/c of fixed call data cost pic.twitter.com/uq9cTYARC4 / Twitter"

the result is that even in the case of end users leveraging rollups, posting call data to Eth beholds them to the gas costs they face today as a result of this fixed ratio.

Note that the chain on which Aztec posts call data is critical for security, because data availability is of chief concern in case Aztec’s rollup provider ceases to function and system state needs to be reconstructed once the provider comes back online.

Note that while a rollup provider going down can only freeze users’ funds in place, with no ability to steal funds, recomputing blockchain state can only happen if state is available (hence data availability).

That’s why for the foreseeable future, we intend to post the rollup’s state to Ethereum–it is for now the Lindy-est, most secure chain with consistent and proven uptime. We’re also excited about exploring our own first-party offchain data availability solution and 3rd-party chains like Celestia.

For now, an Aztec transaction requires the storage of a number of items on-chain:

  • Transaction viewing keys (8,480 gas)²
  • Join-split call data (2,064 gas)³
  • For DeFi transactions, call data for deposit and claim (2,064 * 2)⁴
  • Total: 14,672 gas

Recap & what the future holds

Aztec’s zkRollup has scaled efficiently since the launch of zk.money on mainnet. The impending launch of the Aztec Connect SDK brings up to 100x cost savings for Ethereum DeFi services, all while offering full privacy.

The cost of a private transaction on Aztec will always be cheaper than the cost of a public transaction on Ethereum, despite the added complexity of encrypted transactions — you always get privacy for free (or better than free).

The one elephant in the room is data cost on Ethereum. Call data represents the vast majority (88.8%) of the gas cost for a DeFi transaction. And over time, as proof verification costs fall and the rollup scales further, call data will represent nearly 100% of transaction costs.

At that point, scaling Aztec will also mean optimizing Ethereum.

Next time we’ll cover:

  • Our initiatives to reduce these costs, including taking viewing keys off-chain and pushing for EIP’s reducing the cost of call data on Ethereum
  • How Aztec Connect SDK adds just a little more math to the above

Build with Aztec Connect SDK

Are you a developer who wants to bring privacy to your favorite DeFi protocol? If you build it, we’ll fund it.

Aztec Grants Program: https://airtable.com/shrvglCZ24jaH73oe

Connect Starter: https://github.com/AztecProtocol/aztec-connect-starter.

Help make privacy a no-brainer.

Join the Aztec Community

We’re always on the lookout for talented engineers and applied cryptographers. If joining our mission to bring scalable privacy to Ethereum excites you — check out our open roles.

And continue the conversation with us on Discord or Twitter.

  1. Call data is currently the cheapest form of data storage on Ethereum. It’s a special form of memory used to store function parameters (hence “call” data, because it’s used to call external functions).
  2. Viewing keys are required to view encrypted transactions and read the details of a transaction. Unlike state, they’re not critical for system liveness.
  3. The join-split circuit is a simple formula that ensures Aztec encrypted notes are added (joined) and divided (split) correctly. It follows the simple equivalence (a + b) = (c + d).
  4. The DeFi circuit ensures assets are correctly delivered to the Aztec Rollup (deposited) and returned from the Aztec Rollup (withdrawn).

Privacy for Pennies: Scaling Aztec’s zkRollup was originally published in Aztec on Medium, where people are continuing the conversation by highlighting and responding to this story

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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.

Aztec Network
Aztec Network
22 Jul
xx min read

Introducing the Adversarial Testnet

Aztec’s Public Testnet launched in May 2025.

Since then, we’ve been obsessively working toward our ultimate goal: launching the first fully decentralized privacy-preserving layer-2 (L2) network on Ethereum. This effort has involved a team of over 70 people, including world-renowned cryptographers and builders, with extensive collaboration from the Aztec community.

To make something private is one thing, but to also make it decentralized is another. Privacy is only half of the story. Every component of the Aztec Network will be decentralized from day one because decentralization is the foundation that allows privacy to be enforced by code, not by trust. This includes sequencers, which order and validate transactions, provers, which create privacy-preserving cryptographic proofs, and settlement on Ethereum, which finalizes transactions on the secure Ethereum mainnet to ensure trust and immutability.

Strong progress is being made by the community toward full decentralization. The Aztec Network now includes nearly 1,000 sequencers in its validator set, with 15,000 nodes spread across more than 50 countries on six continents. With this globally distributed network in place, the Aztec Network is ready for users to stress test and challenge its resilience.

Introducing the Adversarial Testnet

We're now entering a new phase: the Adversarial Testnet. This stage will test the resilience of the Aztec Testnet and its decentralization mechanisms.

The Adversarial Testnet introduces two key features: slashing, which penalizes validators for malicious or negligent behavior in Proof-of-Stake (PoS) networks, and a fully decentralized governance mechanism for protocol upgrades.

This phase will also simulate network attacks to test its ability to recover independently, ensuring it could continue to operate even if the core team and servers disappeared (see more on Vitalik’s “walkaway test” here). It also opens the validator set to more people using ZKPassport, a private identity verification app, to verify their identity online.  

Slashing on the Aztec Network

The Aztec Network testnet is decentralized, run by a permissionless network of sequencers.

The slashing upgrade tests one of the most fundamental mechanisms for removing inactive or malicious sequencers from the validator set, an essential step toward strengthening decentralization.

Similar to Ethereum, on the Aztec Network, any inactive or malicious sequencers will be slashed and removed from the validator set. Sequencers will be able to slash any validator that makes no attestations for an entire epoch or proposes an invalid block.

Three slashes will result in being removed from the validator set. Sequencers may rejoin the validator set at any time after getting slashed; they just need to rejoin the queue.

Decentralized Governance

In addition to testing network resilience when validators go offline and evaluating the slashing mechanisms, the Adversarial Testnet will also assess the robustness of the network’s decentralized governance during protocol upgrades.

Adversarial Testnet introduces changes to Aztec Network’s governance system.

Sequencers now have an even more central role, as they are the sole actors permitted to deposit assets into the Governance contract.

After the upgrade is defined and the proposed contracts are deployed, sequencers will vote on and implement the upgrade independently, without any involvement from Aztec Labs and/or the Aztec Foundation.

Start Your Plan of Attack  

Starting today, you can join the Adversarial Testnet to help battle-test Aztec’s decentralization and security. Anyone can compete in six categories for a chance to win exclusive Aztec swag, be featured on the Aztec X account, and earn a DappNode. The six challenge categories include:

  • Homestaker Sentinel: Earn 1 Aztec Dappnode by maximizing attestation and proposal success rates and volumes, and actively participating in governance.
  • The Slash Priest: Awarded to the participant who most effectively detects and penalizes misbehaving validators or nodes, helping to maintain network security by identifying and “slashing” bad actors.
  • High Attester: Recognizes the participant with the highest accuracy and volume of valid attestations, ensuring reliable and secure consensus during the adversarial testnet.
  • Proposer Commander: Awarded to the participant who consistently creates the most successful and timely proposals, driving efficient consensus.
  • Meme Lord: Celebrates the creator of the most creative and viral meme that captures the spirit of the adversarial testnet.
  • Content Chronicler: Honors the participant who produces the most engaging and insightful content documenting the adversarial testnet experience.

Performance will be tracked using Dashtec, a community-built dashboard that pulls data from publicly available sources. Dashtec displays a weighted score of your validator performance, which may be used to evaluate challenges and award prizes.

The dashboard offers detailed insights into sequencer performance through a stunning UI, allowing users to see exactly who is in the current validator set and providing a block-by-block view of every action taken by sequencers.

To join the validator set and start tracking your performance, click here. Join us on Thursday, July 31, 2025, at 4 pm CET on Discord for a Town Hall to hear more about the challenges and prizes. Who knows, we might even drop some alpha.

To stay up-to-date on all things Noir and Aztec, make sure you’re following along on X.

Noir
Noir
26 Jun
xx min read

ZKPassport Case Study: A Look into Online Identity Verification

Preventing sybil attacks and malicious actors is one of the fundamental challenges of Web3 – it’s why we have proof-of-work and proof-of-stake networks. But Sybil attacks go a step further for many projects, with bots and advanced AI agents flooding Discord servers, sending thousands of transactions that clog networks, and botting your Typeforms. Determining who is a real human online and on-chain is becoming increasingly difficult, and the consequences of this are making it difficult for projects to interact with real users.

When the Aztec Testnet launched last month, we wrote about the challenges of running a proof-of-stake testnet in an environment where bots are everywhere. The Aztec Testnet is a decentralized network, and in order to give good actors a chance, a daily quota was implemented to limit the number of new sequencers that could join the validator set per day to start proposing blocks. Using this system, good actors who were already in the set could vote to kick out bad actors, with a daily limit of 5 new sequencers able to join the set each day. However, the daily quota quickly got bottlenecked, and it became nearly impossible for real humans who are operating nodes in good faith to join the Aztec Testnet.

In this case study, we break down Sybil attacks, explore different ways the ecosystem currently uses to prevent them, and dive into how we’re leveraging ZKPassport to prevent Sybil attacks on the Aztec Testnet.

Preventing Sybil Attacks

With the massive repercussions that stem from privacy leaks (see the recent Coinbase incident), any solution to prevent Sybil attacks and prove humanity must not compromise on user privacy and should be grounded in the principles of privacy by design and data minimization. Additionally, given that decentralization underpins the entire purpose of Web3 (and the Aztec Network), joining the network should remain permissionless.

Our goal was to find a solution that allows users to permissionlessly prove their humanity without compromising their privacy. If such a technology exists (spoiler alert: it does), we believe that this has the potential to solve one of the biggest problems faced by our industry: Sybil attacks. Some of the ways that projects currently try to prevent Sybil attacks or prove [humanity] include:

  • “Know Your Customer” (KYC): A process in which users upload a picture or scan of their government ID, which is checked and then retained (indefinitely) by the project, and any “bad actors” are rejected.
    • Pros: High likelihood they are human, although AI has begun to introduce a new set of challenges.
    • Cons: User data is retained and viewable by a centralized entity, which could lead to compromised data and privacy leaks, ultimately impacting the security of the individuals. Also, KYC processes in the age of AI means it is easy to fake a passport as only an image is used to verify and not any biometric data held on the passport itself. Existing KYC practices are outdated, not secure and prone to data leaks increasing personal security risk for the users.
  • On-chain activity and account linking (i.e, Gitcoin passport)
    • Pros: No personal identity data shared (name, location, etc.)
    • Cons: Onchain activity and social accounts are not Sybil-resistant.
  • Small payment to participate
    • Pros: Impractical/financially consequential for bots to join. Effective for centralized infra providers as it can cover the cost they incur from Sybil attacks.
    • Cons: Requires users to pay out of pocket to test the network, and doesn’t prevent bots from participating, and is ineffective for decentralized infra as it is difficult to spread incurred costs to all affected operators.
  • zkEmail
    • Pros: The user shares no private information.
    • Cons: Users cannot be blocked by jurisdiction, for example, it would be impossible to carry out sanctions checks, if required.
  • ZKPassport, a private identity verification app.
    • Pros: User verifies they possess a valid ID without sharing private information. No information is retained therefore no leaks of data can occur impacting the personal security of the user.
    • Cons: Users must have a valid passport or a compatible government ID, in each case, that is not expired.

Both zkEmail and ZKPassport are powered by Noir, the universal language of zk, and are great solutions for preventing Sybil attacks.

With zkEmail, users can do things like prove that they received a confirmation email from a centralized exchange showing that they successfully passed KYC, all without showing any of the email contents or personal information. While this offers a good solution for this use case, we also wanted the functionality of enabling the network to block certain jurisdictions (if needed), without the network knowing where the user is from. This also enables users to directly interface with the network rather than through a third-party email confirmation.

Given this context, ZKPassport was, and is, the perfect fit.

About ZKPassport

For the Aztec Testnet, we’ve integrated ZKPassport to enable node operators to prove they are human and participate in the network. This integration allows the network to dramatically increase the number of sequencers that can be added each day, which is a huge step forward in decentralizing the network with real operators.

ZKPassport allows users to share only the details about themselves that they choose by scanning a passport or government ID. This is achieved using zero-knowledge proofs (ZKPs) that are generated locally on the user’s phone. Implementing client-side zk-proofs in this way enables novel use-cases like age verification, where someone can prove their age without actually sharing how old they are (see the recent report on How to Enable Age Verification on the Internet Today Using Zero-Knowledge Proofs).

As of this week, the ZKPassport app is live and available to download on Google Play and the Apple App Store.

How ZKPassport works

Most countries today issue biometric passports or national IDs containing NFC chips (over 120 countries are currently supported by ZKPassport). These chips contain information on the full name, date of birth, nationality, and even digital photographs of the passport or ID holder. They can also contain biometric data such as fingerprints and iris scans.

By scanning the NFC chip located in their ID document with a smartphone, users generate proof based on a specific request from an app. For example, some apps might require only the user’s age or nationality. In the case of Aztec, no information is needed about the user other than that they do indeed hold a valid passport or ID.

Client-side proving

Once the user installs the ZKPassport app and scans their passport, the proof of identity is generated on the user's smartphone (client-side).

All the private data read from the NFC chip in the passport or ID is processed client-side and never leaves the smartphone (aka: only the user is aware of their data). Only this proof is sent to an app that has requested some information. The app can then verify the validity of the user’s age or nationality, all without actually seeing anything about the user other than what the user has authorized the app to see. In the case of age verification, the user may want to prove that they are over 18, so they’ll create a proof of this on their phone, and the requesting app is able to verify this information without knowing anything else about them.

For the Aztec Testnet, the network only needs to know that the user holds a valid passport, so no information is shared by the user other than “yes, I hold a valid passport or ID.”

Getting started with ZKPassport on Aztec Testnet

This is a nascent and evolving technology, and various phone models, operating systems, and countries are still being optimized for. To ensure this works seamlessly, we’ll be selecting the first cohort of people who have already been running active validators on a rolling basis to help test ZKPassport and provide early feedback.

If someone successfully verifies that they are a valid passport holder, they will be added to a queue to enter the validator set. Once they are in line, they are guaranteed entry. The queue will enable an estimated additional 10% of the current set to be allowed in each day. For example, if 800 sequencers are currently in the set, 80 new sequencers will be allowed to join that day.

This allows existing operators to maintain control of the network in the event that bad actors enter, while dramatically increasing the number of new validators added compared to the current number.

Humanizing Web3  

With ZKPassport now live, the Aztec Testnet is better equipped to distinguish real users from bots, without compromising on privacy or decentralization.

This integration is already enabling more verified human node operators to join the validator set, and the network is ready to welcome more. By leveraging ZKPs and client-side proving, ZKPassport ensures that humanity checks are both secure and permissionless, bringing us closer to a decentralized future that doesn’t rely on trust in centralized authorities.

This is exciting not just for Aztec but for the broader ecosystem. As the network continues to grow and develop, participation must remain open to anyone acting in good faith, regardless of geography or background, while keeping out bots and other malicious actors. ZKPassport makes this possible.

We’re excited to see the community expand, powered by real people helping to build a more private, inclusive, and human Web3.

Stay up-to-date on Noir and Aztec by following Noir and Aztec on X.

Noir
Noir
4 Jun
xx min read

StealthNote: The Decentralized, Private Glassdoor of Web3

Imagine an app that allows users to post private messages while proving they belong to an organization, without revealing their identity. Thanks to zero-knowledge proofs (ZKPs), it's now possible to protect the user’s identity through secure messaging, confidential voting, secured polling, and more. This development in privacy-preserving authentication creates powerful new ways for teams and individuals to communicate on the Internet while keeping aspects of their identity private.

Introducing Private Posting

Compared to Glassdoor, StealthNote is an app that allows users to post messages privately while proving they belong to a specific organization. Built with Noir, an open-source programming language for writing ZK programs, StealthNote utilizes ZKPs to prove ownership of a company email address, without revealing the particular email or other personal information.

Privately Sign In With Google

To prove the particular domain email ownership, the app asks users to sign in using Google. This utilizes Google’s ‘Sign in with Google’ OAuth authorization. OAuth is usually used by external applications for user authorization and returns verified users’ data, such as name, email, and the organization’s domain.

However, using ‘Sign in with Google’ in a traditional way reveals all of the information about the person’s identity to the app. Furthermore, for an app where you want to allow the public to verify the information about a user, all of this information would be made public to the world. That’s where StealthNote steps in, enabling part of the returned user data to stay private (e.g. name and email) and part of it to be publicly verifiable (e.g. company domain).

How StealthNote Works

Understanding JSON Web Tokens (JWTs)

When you "Sign in with Google" in a third-party app, Google returns some information about the user as a JSON Web Token (JWT) – a standard for sending information around the web.

JWTs are just formatted strings that contain a header (some info about the token), a payload (data about the user), and a signature to ensure the integrity and authenticity of the token:

Anyone can verify the authenticity of the above data by verifying that the JWT was signed by Google using their public key.

Adding Private Messages

In the case of StealthNote, we want to authorize the user and prove that they sent a particular message. To make this possible, custom information is added to the JWT token payload – a hashed message. With this additional field, the JWT becomes a digitally signed proof that a particular user sent that exact message.

Protecting the Sender’s Privacy

You can share the message and the JWT with someone and convince them that the message was sent by someone in the company. However, this would require sharing the whole JWT, which includes your name and email, exposing who the sender is. So, how does StealthNote protect this information?

They used a ZK-programming language, Noir, with the following goals in mind:

  • Verify the signature of the JWT using Google's public key
  • Extract the hashed message from the payload
  • Extract the email domain from the payload

The payload and the signature are kept private, meaning they stay on the user’s device and never need to be revealed, while the hashed message, the domain, and the JWT public key are public. The ZKP is generated in the browser, and no private data ever leaves the user's device.

Noir: What is Happening Under the Hood

By executing the program with Noir and generating a proof, the prover (the user who is posting a message) proves that they can generate a JWT signed by some particular public key, and it contains an email field in the payload with the given domain.

When the message is sent to the StealthNote server, the server verifies that the proof is valid as per the StealthNote circuit and validates that the public key in the proof is the same as Google's public key.

Once both checks pass, the server inserts the proof into the database, which then appears in the feed visible for other users. Other users can also verify the proof in the browser. The role of the server is to act as a data storage layer.

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