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Comparing privacy on Aztec, Canton, Starkware, Tempo, and zkSync
Privacy has become a baseline requirement for L1s and L2s who care about bringing real-world users onchain. Users don't want their activity broadcast to competitors or the general public, but applications operating at scale also need some form of auditability, whether for regulators, compliance requirements, or tax reporting. Selective disclosure resolves that tension: privacy by default, with the ability to prove specific facts when required. What separates these networks is not whether they offer that switch, but who gets to hold it.
Aztec, Canton, Starknet, Tempo, and zkSync all offer some form of privacy with selective disclosure, but under the hood they make fundamentally different architectural decisions about who can see your data and who can turn your privacy off. Those decisions determine whether your privacy stays under your own control or sits behind a switch that someone else operates.
Three questions reveal where these networks actually diverge:
The answers determine whether your privacy off-switch is held by a policy, by an operator's good behavior, or by you alone through a cryptographic proof. As you'll see in this post, there are legitimate reasons to use each one with different tradeoffs. Aztec is the only network, however, where that switch stays in the user's hands, answering all three questions without putting a permissioned set of operators or a standing viewing key in control of your privacy. That gives developers the flexibility to build apps that comply with applicable laws while still keeping full privacy under the user's control.
This article will compare the privacy approaches of Aztec, Canton, Starknet, Tempo, and zkSync to give developers insight into the privacy tradeoffs of each network.
Here’s how each network handles the selective disclosure privacy off-switch, and who has control over your privacy:
Each of these networks offers privacy with selective disclosure, but each rests on a different network design with its own tradeoffs. We have ordered them by who holds your privacy off-switch, starting with designs where a third party controls access to your data and ending with designs where that control stays with you. At the top, the switch sits behind a policy promise and an honest operator, and further down it is replaced by proofs that the user generates and controls.
Canton keeps data private by controlling viewing permissions for the various actors on its network. A transaction splits into per-participant views, so each party receives only the sub-transactions that name it, and the parts it is not entitled to never reach it. The sequencer and mediator move those views without reading them, which is real privacy against those roles.
However, the data is still read in plaintext by the participant nodes that host the relevant parties, and in the common regulated-asset pattern where the issuer is a signatory on its own token, the issuer's node sees every transfer. The harder gap is verification, because no third party can reconstruct the global ledger, so correctness rests on the confirming nodes staying honest and their keys staying safe. In practice the off-switch sits with those nodes rather than with you, since you cannot see when your data is read and cannot stop it.
Tempo is designed for payments and uses validity proofs to verify that each zone is executing correctly, while still giving the zone operator full plaintext visibility into every transaction within that zone. Privacy comes from Tempo Zones, which are parallel execution environments connected to the Tempo mainnet.
By design, the zone operator has visibility into all transactions within the zone, while users see only their own and the public sees only a proof that the zone is valid. Token issuers set compliance controls, allowlists, blocklists, and freezes, enforced across zones. The mainnet checks each zone's validity, so execution is verified, while the operator still reads every transaction in plaintext and holds the off-switch over what is revealed. Your privacy is from the public, not from the operator.
zkSync Prividium adds the verifiability piece that Canton lacks. Every batch produces a validity proof settled to Ethereum, so a compromised operator cannot forge state or mint tokens from nothing without also forging a proof, which it cannot do. The tradeoff is that the operator processes every transaction in plaintext and decides who sees what, which means the off-switch stays with the operator and your privacy is from the outside world rather than from the operator itself.
This tradeoff has legitimate uses in high-trust institutional environments. If Bank of America, JPMorgan, and Wells Fargo are transacting on a shared network, a zone where BofA's infrastructure processes BofA-originated transactions satisfies internal control requirements while still delivering genuine ZK privacy from the other banks and the rest of the world. Where this model breaks down is in lower-trust environments where giving an operator full plaintext access and the switch that comes with it holds back product design possibilities.
Starknet's STRK20 breaks from relying on an operator for privacy. It shields ERC-20 balances and transfers in a privacy pool, and every private transaction carries a zero-knowledge proof generated client-side, so no operator sees your plaintext in order to build it.
Disclosure is where STRK20 diverges from Aztec. To join the Starknet Privacy Pool, you register an encrypted viewing key onchain, and it sits there for the life of your participation. On a regulatory request, a designated auditing entity can decrypt that key and trace your complete transaction history, forwards and backwards. StarkWare calls this ‘not a backdoor’ but a carefully scoped access mechanism, and the safeguard is a policy promise that the auditor decrypts only when required. The privacy is cryptographic, but the off-switch is a standing key that someone else holds and can flip whether or not you are watching.
On Aztec your private state lives as encrypted private data that only you can decrypt. The contract developer can choose what state is public and what is private, and whether your encrypted private data is emitted onchain as a private log or shared off-chain instead.
Your transactions get proven client-side on your own device, so no sequencer or operator sees your unencrypted private data. Those proofs settle to Ethereum, which gives the same integrity anchor marketed by Prividium, with every transaction verified and no forged state, but without a single operator who reads your data. The base protocol decentralizes sequencing, proving, and governance, so there is no operator to choose and trust in the first place.
Disclosure is your choice too: you decide who learns your private data, and whether they learn it in encrypted or decrypted form. To grant discovery without readability, you share an app-specific tagging secret that lets an auditor find your data in encrypted form without being able to decrypt and read it. This is enough to prove things calculated from that data, such as a tax basis or a profit and loss figure. Granting permission to actually read the data works differently. There's no per-contract read key you can hand out, because decryption uses your master viewing key, which would unlock all your data across every contract. So instead of sharing a key, you share the data itself, plus a proof that your plaintext is what encrypts to the on-chain ciphertext.
Aztec has true selective disclosure in that you can selectively share it, and nothing else you don’t need to. This is app specific, meaning that private data discoverability access on one app does not grant access on another. Most importantly, the off-switch stays in your hands, and you never need to trust the network to handle access to any of your private data and activity.
This is not just conceptual: here is a working proof-of-concept of this model on Aztec. PrivPNL takes you from private DEX trades through a tagging-key disclosure to a browser-generated ZK proof of your PnL. The auditor verifies a proof while the prover only has to reveal the amount they owe, and your portfolio stays private.
Canton keeps the switch with the participant nodes that read your data in plaintext, so disclosure rests on those nodes staying honest rather than on anything you control. Tempo similarly gives the off-switch to a zone-based node operator, but allows you to verify the correctness of transactions using validity proofs. Prividium hardens that promise with a proof settled to Ethereum, a real improvement, but the operator still reads every transaction and still decides who sees what. This can work well for large institutions, but small to medium sized enterprises are left with the same privacy as their current banks unless they run their own Prividium nodes. STRK20 moves the switch into a standing viewing key and asks you to trust that a designated auditor reaches for it only when needed. In each of these models the real question is not whether your privacy can be switched off, but who gets to do the switching, and whether you would even know it happened.
Aztec takes the operator and the standing key out of the question entirely. You keep the data, you generate the proof, and you disclose the result, one fact at a time and only when you choose to. The off-switch never leaves your hands, and no operator, auditor, or node can reach it on your behalf. This is one of the benefits of a network that offers fully programmable, privacy-preserving smart contracts that put you in control.
Selective disclosure is how privacy survives contact with a regulator, and the model you pick decides who can open your history when you are not looking. On Aztec, that answer is no one but you.
Dive into the technical details: Try a live demo of selective disclosure on Aztec and read the technical article on how it was built.
Integrate with Aztec: Reach out if you are interested in integrating privacy into your project.
Aztec is built on one idea: smart contracts on Ethereum where developers choose what is public and what is private. That doesn't just mean shielded transactions. It means who acts (identity), what they transact (state), and how they execute (computation) can all be private. Aztec makes end-to-end privacy possible; even the contracts themselves can be private.
But privacy also has to be practical. Aztec integrates private and public execution in the same contract, so apps can seamlessly weave together private and public state. Every account is a smart contract, letting users grant granular, revocable access for selective disclosure, which is useful for compliance, tax reporting, or agent permissions.
Finally, Aztec is a decentralized L2, with 3,500+ sequencers participating in the network today. That permissionlessness is what makes Aztec a credible foundation for a global privacy layer.
In this article we’re going to explore the Aztec stack and how we make programmable privacy a reality. We’ll answer questions like ‘what can you do on Aztec?’, ‘how does it all work?’, and ‘what are the core layers of the system that makes it all possible?’
The four layers of the Aztec stack, all live today on the Alpha network:
Aztec smart contracts are written in Noir, a programming language with Rust-like syntax optimized for writing private programs. Noir is an open-source project developed by Aztec and is now the industry-leading language for writing private apps using zero-knowledge proofs. Let’s dive into what Noir is, and why we use it as the building block for writing smart contracts.
Writing zk programs is extremely difficult without a background in cryptography. When developing Noir, our first goal was to create a highly optimized and easy-to-write zk Domain Specific Language (zkDSL) where developers don’t need to know any of the underlying mathematics. As a result, Noir handles all the cryptographic complexities, and will automatically convert your code into fancy zk circuits.
Noir compiles down to the Abstract Circuit Intermediate Representation (ACIR), an adaptable intermediary language that makes it easy to plug in a variety of popular proving backends. These proving backends, such as Aztec’s Barretenberg proving system, take the compiled zero-knowledge circuits and generate proofs attesting to the validity of the program’s execution, all without revealing any private inputs. From authorization systems that keep a password on the user's device, to complex onchain state channels with recursive proofs to verify offchain state; Noir and a proving backend handle everything from compilation to cryptography for you.
In addition to simplifying the developer experience, we also wanted to make it intuitive to specify which elements you want to keep private and which you want to make public. With Noir, privacy is baked in as a default, so all variables and functions are automatically kept completely private, and executed on the user’s device.
If you want to make any part of your code public, you can do so by simply adding a pub attribute.
Noir on its own is great for writing programs that need to execute stateless functions, such as proving that you reside in a specific country based on passport data, or that you hold a certain number of tokens without revealing how many. Projects are already starting to build with Noir outside of Aztec on Base, Scroll, Starknet, and other chains. However, if you are looking to write privacy-preserving apps that store private state data onchain, it’s helpful to utilize a smart contract library that deliberately handles those complexities for you. That’s exactly what we’ve built at Aztec and what we’ll explore in the next section.
Aztec smart contracts leverage Noir to create apps with onchain private and public state. This section covers how smart contracts work on Aztec and how you deploy and interact with your contracts.
An Aztec smart contract is a set of public and private functions written in Noir, deployed on the Aztec Network. They are written using the Aztec.nr framework which handles all the cryptography under the hood for managing private and public state and interacting with other contracts on the network.
To build useful applications, developers need to be able to incorporate both private and public components into their contracts. For example, an onchain voting contract might want to keep the information of the voter private and prevent someone from voting twice, but publicly display how many votes have been cast, and the outcome.
Because contracts are written in Noir, this functionality is as easy as adding a ‘private’ annotation above your function. The following function will be executed privately on the user device, allowing a user to cast a vote without revealing their address:
The output of this private, local execution will be sent to the network, where the correctness of execution is verified and public function calls are executed. The following function is designed to be executed publicly, adding a vote to the total tally without revealing where it came from.
To seamlessly weave together private and public components that can easily interact with onchain state, Aztec smart contracts utilize the Aztec.nr framework to execute private functions on the user’s device and bundle the proofs for these transactions together with the public functions that will be executed by the Aztec Virtual Machine (AVM).
This framework adds the functionality needed to build onchain, privacy-preserving apps, including defining contracts, accessing private or public context, and interacting with the Aztec Network. Similar to how a vanilla Noir program would compile down into zk circuits, Aztec smart contracts are compiled into zk circuits for private functions or AVM bytecode for public functions, and stored in the Aztec contract tree.
Aztec accounts are also written as smart contracts, implementing what is known as account abstraction. Account abstraction allows application developers to create programmable accounts to dramatically improve user experience, including social recovery, sponsored transactions, and multi-factor authentication. It also makes compliance practical, allowing for granular access controls on accounts.
The Aztec Network is the only decentralized L2 on Ethereum. There are currently over 3,500 sequencers running the alpha network. View the live block explorer for the alpha network.
In order for a network to fully protect users and their data, it must guarantee three levels of privacy:
When you write Aztec smart contracts, everything listed above is taken care of for you. As discussed in the previous two sections, you can easily opt into privacy protections at a granular level by weaving together public and private functions.
To understand how all of these components fit together, let’s examine how a transaction is executed on the Aztec Network.
When a user interacts with your application, private functions are executed client-side on the user’s device: a phone, a personal computer, etc. This happens in a private execution environment (PXE) that is able to create highly-efficient zk proofs even on browsers and mobile devices. Any private state updates are added to the state of the network in an append-only database (UTXO tree). Because the proof is generated client-side, no information can be leaked about the inputs, outputs, accounts, or even the functions that were executed.
On the other hand, public transactions are bundled together with the private client-side proofs and sent off to the Aztec Network, powered by a decentralized network of independent community-run sequencers. Sequencers check the validity of private execution proofs, execute any public functions and update the public state, propose blocks, and publish state updates (“diffs”) to Ethereum L1. Sequencers also coordinate with a decentralized network of provers who compute the final proof for every Aztec “epoch” - defined as a contiguous sequence of 32 L2 blocks - and publish it to Ethereum. Any public functions executed by sequencers update an account-based database similar to Ethereum.
Sequencer and prover roles are fully permissionless. Anyone can spin up the required hardware and join the sequencer set or run provers and start bidding to produce proofs of Aztec epochs.
Aztec delivers on a simple but powerful idea: smart contracts on Ethereum where you choose what's public and what's private across identity, data, and compute. The four layers we've walked through are what make that possible.
Noir gives developers a Rust-like language for writing zero-knowledge programs without a cryptography background, with privacy as the default. Aztec smart contracts build on Noir through the Aztec.nr framework, letting you weave private and public functions into a single contract and use account abstraction to unlock granular access controls for compliance, tax reporting, and selective disclosure. The Aztec Network is the only decentralized L2 on Ethereum, with over 3,500 sequencers powering end-to-end programmable privacy across data, identity, and compute. And it all settles to Ethereum, inheriting L1's economic security.
The result is the first practical platform for privacy on Ethereum, and a credible candidate to become the global settlement layer of the future.
Now it's your turn to build. Head to docs.aztec.network to ship your first privacy-preserving app.
Follow Aztec on X for updates on the current state of the network.
Last week, PSE published an insightful and comprehensive user-research piece on private transfers on Ethereum. They interviewed 38 teams in the space and asked what's broken, what's missing, what builders wish they had. The list reads like a wishlist of features every privacy app on L1 is currently trying to engineer towards. It's the kind of rigorous, builder-grounded research the privacy ecosystem has needed.
We read the list. It's the list we've been building against for years.
Aztec solves all of these problems. Every requested feature already lives on Aztec. The proving system, the private contract language, the decentralized network, the privacy wallet architecture, the key model, the snark-friendliness: all of Aztec was built against this list before it was a list.
What follows is a walkthrough. For each of PSE's top technical findings, here's the feature builders are asking for, and how it works on Aztec today.
Ethereum Problem: Proof generation is too slow on user devices, especially mobile. Elliptic-curve pairing operations are a specific bottleneck. Server-side proving is a censorship and privacy leak vector. Sub-second proving was the stated threshold.
Aztec solution: Proving on Aztec runs locally in the PXE (Private eXecution Environment, pronounced "pixie"), so no data ever leaves the user's device. Chonk, our client-side zk proving system, is ruthlessly optimised for fast recursive proving on low-memory devices like phones, native and in-browser. Years of optimization have already gone in, and we're still finding more. It’s best in class and we haven’t even merged-in GPU acceleration yet!
The slow pairing checks that PSE's interviewees called out as a bottleneck aren’t a problem with Aztec; pairings are simply batched together and deferred away from the user's device, handled by the more powerful network instead, without leaking any information. With such a powerful local prover, there’s little need to outsource proving to an untrusted party.
Ethereum Problem: Verifying a ZK proof on Ethereum is prohibitively expensive. A Groth16 proof for a private transfer costs several hundred thousand L1 gas. A Halo2 (KZG Plonk) proof can cost approximately one million gas
Aztec solution: Aztec amortises L1 verification gas across all transactions in the rollup. At current network throughput, that cost is split across roughly 2,000 users per proof. Later this year, it’s slated to be split across ~20,000. Rollup costs are also partially subsidised by Aztec block rewards.
Net result: hundreds of L1 gas per user instead of millions. Plus cheap L2 gas. The user pays pennies for an Aztec transaction.
Ethereum Problem: Wrapping and unwrapping tokens leaks privacy and breaks composability. Smart contracts can't easily interact with encrypted balances. Private state is isolated; contract state is normally shared.
Aztec solution: Private state is not isolated on Aztec. The private state of one contract can be composed with that of another. This can unlock new privacy-preserving DeFi patterns directly on Aztec.
A single private transaction can call a stack of private functions across multiple contracts, with private inputs, private state transitions, and privacy over which functions were even executed and how many. Observers see that a transaction landed. They do not see what happened inside it. Stew on that for a second: a call stack of nested private functions across contracts written by different developers, each causing state transitions, all completely private.
Aztec also runs public functions, similar to Ethereum, inside the same smart contract, so you can build existing DeFi primitives on Aztec.
For Ethereum DeFi specifically, Aztec has a tidy L1-to-L2 messaging layer. Private balances can be unshielded to interact with L1 protocols and shielded back, without leaking who did the interaction and without leaky public gas payments. And for private DeFi primitives that need genuinely shared private state (state nobody knows the value of, but which anyone can mutate), people have built Aztec contracts that compose conventional Aztec private state with co-snark or FHE sidecars.
Private and public state are peers inside a single Aztec smart contract. Builders mix and match.
Ethereum Problem: Entry and exit points are the dominant privacy leak, not the protocol itself. Depositing and quickly withdrawing makes identity analysis trivial.
Aztec solution: The main fix is to stop crossing the boundary so often. (Or even if you do cross the boundary, Aztec has leakage protections).
Imagine if thousands of private smart contracts lived on the same network and could call each other without leaking which contracts were called, which arguments were passed, or what was returned. Imagine they all shared one global note tree and one global nullifier tree. That's Aztec. Once funds are inside, users don't need to keep crossing the private/public boundary to do useful things: Aztec is its own rich environment for composable, private execution of smart contracts.
Even when a private function does need to call a public function – be it an L1 DeFi contract, or a native public function within Aztec – the developer controls the information they reveal; not the protocol. The call can even be "incognito" to hide msg_sender. A single environment for many private apps to thrive also means re-usable tooling for builders.
Ethereum Problem: Privacy features (per-dapp addresses, private transfers) aren't natively integrated into major wallets. Reliance on dapp-specific UIs damages UX.
Aztec solution: Ethereum wallets weren't built for any of this, and they don't need to be: the chain underneath them has no private state to protect. Aztec wallets are an entirely new category of software.
Aztec wallets are able to manage all these new privacy-centric concepts:
Aztec wallets are in active development, and this is an area where we expect many teams to build different wallets that are customized to various user needs. An early wallet is already baked into the protocol for developers to start using today.
Ethereum Problem: Encrypted tokens and many privacy protocols depend on external networks for encryption, decryption, or relaying. Threshold-decryption committees and TEE hardware vendors are added trust assumptions on top of the chain itself.
Aztec solution: Aztec's private and public execution environments are not reliant on external networks. Aztec is its own decentralised network: ~4,000 validators stake on it, block proposers are randomly selected, a random committee attests, and a decentralised set of provers proves the rollup's execution. Validity is ultimately backed by cryptographic proofs settled on Ethereum.
External networks (co-snark networks, TEEs, MPC or FHE sidecars) become an opt-in choice for the specific case of private shared state. The trust tradeoffs there are something the contract developer signs up for explicitly, not a tax every user pays on every transaction by default.
Ethereum Problem: Keccak is inefficient to prove inside ZK circuits. There is no native support for a ZK-friendly hash like Poseidon.
Aztec solution: Poseidon2 is enshrined across the entire Aztec protocol, for rapid proving of every tx. Every Aztec state tree, the proving system, the innards of the protocol; everywhere. Reading and writing state inside a circuit is as cheap as it gets.
Keccak, SHA, and Blake hashes are still available through optimised Noir libraries when contracts need them for L1 interoperability. The default is ZK-friendly; the L1-friendly hashes are there when you reach for them.
Ethereum Problem: Syncing private state (scanning for incoming notes and events) is a client-side bottleneck. Users wait for scans to complete before seeing their balance. Tachyon-style oblivious sync was cited as a path forward.
Aztec solution: Brute-force syncing of private state is rarely needed. Most real-world use cases involve a sender and recipient who can establish a shared secret offchain first.
From that shared secret, both parties can derive a sequence of random-looking “tags”. Each encrypted note log is prepended with the next tag in the sequence. The recipient already knows the next tag, so they know exactly what to query. Note discovery happens in seconds, not minutes. The scheme slots cleanly into PIR or mixnet approaches for extra privacy on the query itself, and smart contracts that don't trust senders to use the correct tag can just constrain it inside the circuit.
That’s not to say that Aztec requires interactivity between all senders and recipients. For genuinely non-interactive use cases (recipient can't talk to the sender before the transfer), Aztec enables devs to customize both their log emission and their note-discovery logic however they like. (Aztec also has ways to speed up the brute-force scanning approach from "scan the whole chain" to "scan a tiny subset of non-interactive handshake txs"
Ethereum Problem: Shielded pools are fragmented across dapps and chains, reducing the effective privacy set for all users. Each new privacy protocol must bootstrap its own.
Aztec solution: There is one global note tree and one global nullifier tree on Aztec, shared by every smart contract on the network. Every private app contributes to and draws from the same privacy set. No per-app bootstrap. No walled gardens.
Private payments, private swaps, lending, payroll, treasury, identity attestations: all of them land in the same global commitment set, by construction.
Ethereum Problem: Ethereum developer tooling lacks support for private transfers and private state. Standards for private tokens, compliance, and wallet interactions are missing. Many privacy teams are small, with short runway and expensive audits.
Aztec solution: Aztec ships the full toolchain for private contracts: Noir for writing private logic, the Aztec smart contract framework with macros that hide the protocol mess so devs can focus on app logic, the PXE for keys / state / syncing / proof generation, a JS SDK, a local node for testing, a CLI, and a real, live, decentralised L2.
The mental overhead of building a privacy protocol on Aztec collapses to "just write the app logic." Here is an example of a complete private transfer function on Aztec:
#[authorize_once("from", "authwit_nonce")]
#[external("private")]
fn transfer_in_private(from: AztecAddress, to: AztecAddress, amount: u128, authwit_nonce: Field) {
self.storage.balances.at(from).sub(amount).deliver(MessageDelivery.ONCHAIN_CONSTRAINED);
self.storage.balances.at(to).add(amount).deliver(MessageDelivery.ONCHAIN_CONSTRAINED);
}
Look at how simple that is.
A two-line function body.
Two lines.
Aztec takes care of the rest.
Behind those #[...] macros, the framework handles: caller authorisation, note syncing, fetching notes from the user's private db, Merkle membership proofs against the global note tree, safe nullifier creation (without leaking master secrets to the circuit), randomness for new notes, encrypted ciphertext generation, log tagging for fast recipient discovery, and public-input population. The PXE handles key management, private state, and proof generation. The smart contract itself contains its own message-processing logic for log discovery, decryption, and storage on the recipient side.
If you want whitelists, blacklists, association sets, custom tx authorisation, viewing-key hierarchies, temporary view access, selective disclosure to specific counterparties, just import a Noir library. Want something more adventurous than private payments? Same toolchain.
PSE's findings are not ten unrelated bugs. They're the same problem refracted ten ways: privacy retrofitted onto a chain that was not designed for it yields bad tradeoffs.
Aztec was designed against this list before it was a list. One global note tree and one global nullifier tree. Private and public state inside the same contract. Compose calls between private contracts without leaking anything. Fast client-side proving on phones via Chonk. Snark-friendliness everywhere. Rollup-amortised L1 gas costs, fractions of a cent per user. Native account abstraction with private fee paymasters. No painfully slow private state syncing: a tagging-based note discovery scheme that runs in seconds. An entirely new category of wallet that treats privacy as a first-class concern. Simple, high-level smart contract syntax that collapses a basic private token transfer function into two lines.
There were 10 privacy features Ethereum devs wanted, all of them live on Aztec. The infrastructure is in place. Build the thing.
Aztec is the blockchain that solved the privacy problem. Start at docs.aztec.network or read the architecture deep-dive on The Best of Both Worlds: How Aztec Blends Private and Public State.
Alpha is live: a fully feature-complete, privacy-first network. The infrastructure is in place, privacy is native to the protocol, and developers can now build truly private applications.
Nine years ago, we set out to redesign blockchain for privacy. The goal: create a system institutions can adopt while giving users true control of their digital lives. Privacy band-aids are coming to Ethereum (someday), but it’s clear we need privacy now, and there’s an arms race underway to build it. Privacy is complex, it’s not a feature you can bolt-on as an afterthought. It demands a ground-up approach, deep tech stack integration, and complete decentralization.
In November 2025, the Aztec Ignition Chain went live as the first decentralized L2 on Ethereum, it’s the coordination layer that the execution layer sits on top of. The network is not operated by the Aztec Labs or the Aztec Foundation, it’s run by the community, making it the true backbone of Aztec.
With the infrastructure in place and a unanimous community vote, the network enters Alpha.
Alpha is the first Layer 2 with a full execution environment for private smart contracts. All accounts, transactions, and the execution itself can be completely private. Developers can now choose what they want public and what they want to keep private while building with the three privacy pillars we have in place across data, identity, and compute.
These privacy pillars, which can be used individually or combined, break down into three core layers:
Alpha is feature complete–meaning this is the only full-stack solution for adding privacy to your business or application. You build, and Aztec handles the cryptography under the hood.
It’s Composable. Private-preserving contracts are not isolated; they can talk to each other and seamlessly blend both private and public state across contracts. Privacy can be preserved across contract calls for full callstack privacy.
No backdoor access. Aztec is the only decentralized L2, and is launching as a fully decentralized rollup with a Layer 1 escape hatch.
It’s Compliant. Companies are missing out on the benefits of blockchains because transparent chains expose user data, while private networks protect it, but still offer fully customizable controls. Now they can build compliant apps that move value around the world instantly.
Developers can explore our privacy primitives across data, identity, and compute and start building with them using the documentation here. Note that this is an early version of the network with known vulnerabilities, see this post for details. While this is the first iteration of the network, there will be several upgrades that secure and harden the network on our path to Beta. If you’d like to learn more about how you can integrate privacy into your project, reach out here.
To hear directly from our Cofounders, join our live from Cannes Q&A on Tuesday, March 31st at 9:30 am ET. Follow us on X to get the latest updates from the Aztec Network.
On Wednesday 17 March 2026 our team discovered a new vulnerability in the Aztec Network. Following the analysis, the vulnerability has been confirmed as a critical vulnerability in accordance with our vulnerability matrix.
The vulnerability affects the proving system as a whole, and is not mitigated via public re-execution by the committee of validators. Exploitation can lead to severe disruption of the protocol and theft of user funds.
In accordance with our policy, fixes for the network will be packaged and distributed with the “v5” release of the network, currently planned for July 2026.
The actual bug and corresponding patch will not be publicly disclosed until “v5.”
Aztec applications and portals bridging assets from Layer 1s should warn users about the security guarantees of Alpha, in particular, reminding users not to put in funds they are not willing to lose. Portals or applications may add additional security measures or training wheels specific to their application or use case.
We will shortly establish a bug tracker to show the number and severity of bugs known to us in v4. The tracker will be updated as audits and security researchers discover issues. Each new alpha release will get its own tracker. This will allow developers and users to judge for themselves how they are willing to use the network, and we will use the tracker as a primary determinant for whether the network is ready for a "Beta" label.
We have identified a vulnerability in barretenberg allowing inclusion of incorrect proofs in the Aztec Network mempool, and ask all nodes to upgrade to versions v.4.1.2 or later.
We’d like to thank Consensys Diligence & TU Vienna for a recent discovery of a separate vulnerability in barretenberg categorized as medium for the network and critical for Noir:
We have published a fixed version of barretenberg.
We’d also like to thank Plainshift AI for discovery, reproduction, and reporting of one more vulnerability in the Aztec Network and their ongoing work to help secure the network.
Privacy has become a baseline requirement for L1s and L2s who care about bringing real-world users onchain. Users don't want their activity broadcast to competitors or the general public, but applications operating at scale also need some form of auditability, whether for regulators, compliance requirements, or tax reporting. Selective disclosure resolves that tension: privacy by default, with the ability to prove specific facts when required. What separates these networks is not whether they offer that switch, but who gets to hold it.
Aztec, Canton, Starknet, Tempo, and zkSync all offer some form of privacy with selective disclosure, but under the hood they make fundamentally different architectural decisions about who can see your data and who can turn your privacy off. Those decisions determine whether your privacy stays under your own control or sits behind a switch that someone else operates.
Three questions reveal where these networks actually diverge:
The answers determine whether your privacy off-switch is held by a policy, by an operator's good behavior, or by you alone through a cryptographic proof. As you'll see in this post, there are legitimate reasons to use each one with different tradeoffs. Aztec is the only network, however, where that switch stays in the user's hands, answering all three questions without putting a permissioned set of operators or a standing viewing key in control of your privacy. That gives developers the flexibility to build apps that comply with applicable laws while still keeping full privacy under the user's control.
This article will compare the privacy approaches of Aztec, Canton, Starknet, Tempo, and zkSync to give developers insight into the privacy tradeoffs of each network.
Here’s how each network handles the selective disclosure privacy off-switch, and who has control over your privacy:
Each of these networks offers privacy with selective disclosure, but each rests on a different network design with its own tradeoffs. We have ordered them by who holds your privacy off-switch, starting with designs where a third party controls access to your data and ending with designs where that control stays with you. At the top, the switch sits behind a policy promise and an honest operator, and further down it is replaced by proofs that the user generates and controls.
Canton keeps data private by controlling viewing permissions for the various actors on its network. A transaction splits into per-participant views, so each party receives only the sub-transactions that name it, and the parts it is not entitled to never reach it. The sequencer and mediator move those views without reading them, which is real privacy against those roles.
However, the data is still read in plaintext by the participant nodes that host the relevant parties, and in the common regulated-asset pattern where the issuer is a signatory on its own token, the issuer's node sees every transfer. The harder gap is verification, because no third party can reconstruct the global ledger, so correctness rests on the confirming nodes staying honest and their keys staying safe. In practice the off-switch sits with those nodes rather than with you, since you cannot see when your data is read and cannot stop it.
Tempo is designed for payments and uses validity proofs to verify that each zone is executing correctly, while still giving the zone operator full plaintext visibility into every transaction within that zone. Privacy comes from Tempo Zones, which are parallel execution environments connected to the Tempo mainnet.
By design, the zone operator has visibility into all transactions within the zone, while users see only their own and the public sees only a proof that the zone is valid. Token issuers set compliance controls, allowlists, blocklists, and freezes, enforced across zones. The mainnet checks each zone's validity, so execution is verified, while the operator still reads every transaction in plaintext and holds the off-switch over what is revealed. Your privacy is from the public, not from the operator.
zkSync Prividium adds the verifiability piece that Canton lacks. Every batch produces a validity proof settled to Ethereum, so a compromised operator cannot forge state or mint tokens from nothing without also forging a proof, which it cannot do. The tradeoff is that the operator processes every transaction in plaintext and decides who sees what, which means the off-switch stays with the operator and your privacy is from the outside world rather than from the operator itself.
This tradeoff has legitimate uses in high-trust institutional environments. If Bank of America, JPMorgan, and Wells Fargo are transacting on a shared network, a zone where BofA's infrastructure processes BofA-originated transactions satisfies internal control requirements while still delivering genuine ZK privacy from the other banks and the rest of the world. Where this model breaks down is in lower-trust environments where giving an operator full plaintext access and the switch that comes with it holds back product design possibilities.
Starknet's STRK20 breaks from relying on an operator for privacy. It shields ERC-20 balances and transfers in a privacy pool, and every private transaction carries a zero-knowledge proof generated client-side, so no operator sees your plaintext in order to build it.
Disclosure is where STRK20 diverges from Aztec. To join the Starknet Privacy Pool, you register an encrypted viewing key onchain, and it sits there for the life of your participation. On a regulatory request, a designated auditing entity can decrypt that key and trace your complete transaction history, forwards and backwards. StarkWare calls this ‘not a backdoor’ but a carefully scoped access mechanism, and the safeguard is a policy promise that the auditor decrypts only when required. The privacy is cryptographic, but the off-switch is a standing key that someone else holds and can flip whether or not you are watching.
On Aztec your private state lives as encrypted private data that only you can decrypt. The contract developer can choose what state is public and what is private, and whether your encrypted private data is emitted onchain as a private log or shared off-chain instead.
Your transactions get proven client-side on your own device, so no sequencer or operator sees your unencrypted private data. Those proofs settle to Ethereum, which gives the same integrity anchor marketed by Prividium, with every transaction verified and no forged state, but without a single operator who reads your data. The base protocol decentralizes sequencing, proving, and governance, so there is no operator to choose and trust in the first place.
Disclosure is your choice too: you decide who learns your private data, and whether they learn it in encrypted or decrypted form. To grant discovery without readability, you share an app-specific tagging secret that lets an auditor find your data in encrypted form without being able to decrypt and read it. This is enough to prove things calculated from that data, such as a tax basis or a profit and loss figure. Granting permission to actually read the data works differently. There's no per-contract read key you can hand out, because decryption uses your master viewing key, which would unlock all your data across every contract. So instead of sharing a key, you share the data itself, plus a proof that your plaintext is what encrypts to the on-chain ciphertext.
Aztec has true selective disclosure in that you can selectively share it, and nothing else you don’t need to. This is app specific, meaning that private data discoverability access on one app does not grant access on another. Most importantly, the off-switch stays in your hands, and you never need to trust the network to handle access to any of your private data and activity.
This is not just conceptual: here is a working proof-of-concept of this model on Aztec. PrivPNL takes you from private DEX trades through a tagging-key disclosure to a browser-generated ZK proof of your PnL. The auditor verifies a proof while the prover only has to reveal the amount they owe, and your portfolio stays private.
Canton keeps the switch with the participant nodes that read your data in plaintext, so disclosure rests on those nodes staying honest rather than on anything you control. Tempo similarly gives the off-switch to a zone-based node operator, but allows you to verify the correctness of transactions using validity proofs. Prividium hardens that promise with a proof settled to Ethereum, a real improvement, but the operator still reads every transaction and still decides who sees what. This can work well for large institutions, but small to medium sized enterprises are left with the same privacy as their current banks unless they run their own Prividium nodes. STRK20 moves the switch into a standing viewing key and asks you to trust that a designated auditor reaches for it only when needed. In each of these models the real question is not whether your privacy can be switched off, but who gets to do the switching, and whether you would even know it happened.
Aztec takes the operator and the standing key out of the question entirely. You keep the data, you generate the proof, and you disclose the result, one fact at a time and only when you choose to. The off-switch never leaves your hands, and no operator, auditor, or node can reach it on your behalf. This is one of the benefits of a network that offers fully programmable, privacy-preserving smart contracts that put you in control.
Selective disclosure is how privacy survives contact with a regulator, and the model you pick decides who can open your history when you are not looking. On Aztec, that answer is no one but you.
Dive into the technical details: Try a live demo of selective disclosure on Aztec and read the technical article on how it was built.
Integrate with Aztec: Reach out if you are interested in integrating privacy into your project.
Alpha is live: a fully feature-complete, privacy-first network. The infrastructure is in place, privacy is native to the protocol, and developers can now build truly private applications.
Nine years ago, we set out to redesign blockchain for privacy. The goal: create a system institutions can adopt while giving users true control of their digital lives. Privacy band-aids are coming to Ethereum (someday), but it’s clear we need privacy now, and there’s an arms race underway to build it. Privacy is complex, it’s not a feature you can bolt-on as an afterthought. It demands a ground-up approach, deep tech stack integration, and complete decentralization.
In November 2025, the Aztec Ignition Chain went live as the first decentralized L2 on Ethereum, it’s the coordination layer that the execution layer sits on top of. The network is not operated by the Aztec Labs or the Aztec Foundation, it’s run by the community, making it the true backbone of Aztec.
With the infrastructure in place and a unanimous community vote, the network enters Alpha.
Alpha is the first Layer 2 with a full execution environment for private smart contracts. All accounts, transactions, and the execution itself can be completely private. Developers can now choose what they want public and what they want to keep private while building with the three privacy pillars we have in place across data, identity, and compute.
These privacy pillars, which can be used individually or combined, break down into three core layers:
Alpha is feature complete–meaning this is the only full-stack solution for adding privacy to your business or application. You build, and Aztec handles the cryptography under the hood.
It’s Composable. Private-preserving contracts are not isolated; they can talk to each other and seamlessly blend both private and public state across contracts. Privacy can be preserved across contract calls for full callstack privacy.
No backdoor access. Aztec is the only decentralized L2, and is launching as a fully decentralized rollup with a Layer 1 escape hatch.
It’s Compliant. Companies are missing out on the benefits of blockchains because transparent chains expose user data, while private networks protect it, but still offer fully customizable controls. Now they can build compliant apps that move value around the world instantly.
Developers can explore our privacy primitives across data, identity, and compute and start building with them using the documentation here. Note that this is an early version of the network with known vulnerabilities, see this post for details. While this is the first iteration of the network, there will be several upgrades that secure and harden the network on our path to Beta. If you’d like to learn more about how you can integrate privacy into your project, reach out here.
To hear directly from our Cofounders, join our live from Cannes Q&A on Tuesday, March 31st at 9:30 am ET. Follow us on X to get the latest updates from the Aztec Network.
The Ignition Chain launched late last year, as the first fully decentralized L2 on Ethereum– a huge milestone for decentralized networks. The team has reinvented what true programmable privacy means, building the execution model from the ground up— combining the programmability of Ethereum with the privacy of Zcash in a single execution environment.
Since then, the network has been running with zero downtime with 3,500+ sequencers and 50+ provers across five continents. With the infrastructure now in place, the network is fully in the hands of the community, and the culmination of the past 8 years of work is now converging.
Major upgrades have landed across four tracks: the execution layer, the proving system, the programming language, Noir, and the decentralization stack. Together, these milestones deliver on Aztec’s original promise, a system where developers can write fully programmable smart contracts with customizable privacy.
The infrastructure is in place. The code is ready. And we’re ready to ship.
The execution layer delivers on Aztec's core promise: fully programmable, privacy-preserving smart contracts on Ethereum.
A complete dual state model is now in place–with both private and public state. Private functions execute client-side in the Private Execution Environment (PXE), running directly in the user's browser and generating zero-knowledge proofs locally, so that private data never leaves the original device. Public functions execute on the Aztec Virtual Machine (AVM) on the network side.
Aztec.js is now live, giving developers a full SDK for managing accounts and interacting with contracts. Native account abstraction has been implemented, meaning every account is a smart contract with customizable authentication rules. Note discovery has been solved through a tagging mechanism, allowing recipients to efficiently query for relevant notes without downloading and decrypting everything on the network.
Contract standards are underway, with the Wonderland team delivering AIP-20 for tokens and AIP-721 for NFTs, along with escrow contracts and logic libraries, providing the production-ready building blocks for the Alpha Network.
The proving system is what makes Aztec's privacy guarantees real, and it has deep roots.
In 2019, Aztec's cofounder Zac Williamson and Chief Scientist Ariel Gabizon introduced PLONK, which became one of the most widely used proving systems in zero-knowledge cryptography. Since then, Aztec's cryptographic backend, Barretenberg, has evolved through multiple generations, each facilitating faster, lighter, and more efficient proving than the last. The latest innovation, CHONK (Client-side Highly Optimized ploNK), is purpose-built for proving on phones and browsers and is what powers proof generation for the Alpha Network.
CHONK is a major leap forward for the user experience, dramatically reducing the memory and time required to generate proofs on consumer devices. It leverages best-in-class circuit primitives, a HyperNova-style folding scheme for efficiently processing chains of private function calls, and Goblin, a hyper-efficient purpose-built recursion acceleration scheme. The result is that private transactions can be proven on the devices people actually use, not just powerful servers.
This matters because privacy on Aztec means proofs are generated on the user's own device, keeping private data private. If proving is too slow or too resource-intensive, privacy becomes impractical. CHONK makes it practical.
Decentralization is what makes Aztec's privacy guarantees credible. Without it, a central operator could censor transactions, introduce backdoors, or compromise user privacy at will.
Aztec addressed this by hardcoding decentralized sequencing, proving, and governance directly into the base protocol. The Ignition Chain has proven the stability of this consensus layer, maintaining zero downtime with over 3,500 sequencers and 50+ provers running across five continents. Aztec Labs and the Aztec Foundation run no sequencers and do not participate in governance.
Noir 1.0 is nearing completion, bringing a stable, production-grade language within reach. Aztec's own protocol circuits have been entirely rewritten in Noir, meaning the language is already battle-tested at the deepest layer of the stack.
Internal and external audits of the compiler and toolchain are progressing in parallel, and security tooling including fuzzers and bytecode parsers is nearly finished. A stable, audited language means application teams can build on Alpha with confidence that the foundation beneath them won't shift.
The code for Alpha Network, a functionally complete and raw version of the network, is ready.
The Alpha Network brings fully programmable, privacy-preserving smart contracts to Ethereum for the first time. It's the culmination of years of parallel work across the four tracks in the Aztec Roadmap. Together, they enable efficient client-side proofs that power customizable smart contracts, letting users choose exactly what stays private and what goes public.
No other project in the space is close to shipping this.
The code is written. The network is running. All the pieces are in place. The governance proposal is now live on the forum and open for discussion. Read through it, ask questions, poke holes, and help shape the path forward.
Once the community is aligned, the proposal moves to a vote. This is how a decentralized network upgrades. Not by a team pushing a button, but by the people running it.
Programmable privacy will unlock a renaissance in onchain adoption. Real-world applications are coming and institutions are paying attention. Alpha represents the culmination of eight years of intense work to deliver privacy on Ethereum.
Now it needs to be battle-tested in the wild.
View the updated product roadmap here and join us on Thursday, March 5th, at 3 pm UTC on X to hear more about the most recent updates to our product roadmap.
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.
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 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 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 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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:
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.”
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."
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."
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."
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:
"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.
Halo2: Binary decomposition
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)
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.
"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’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.
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.
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.
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.
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:
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.
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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.
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:
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.
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.
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.
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.”
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.
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.
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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.
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.
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).
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.
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.
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:
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.
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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