Aztec Network
Sep 13th, 2023
## min read

Privacy Abstraction with Aztec

This article explores how Aztec achieves privacy abstraction in its technology, a critical aspect for secure and private blockchain transactions.

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Aztec’s architecture is a departure from the current trend in blockchains of horizontal scaling via more general-purpose EVM-compatible execution environments. At Aztec Labs we joke we’re the first protocol not to build a zkEVM.

Instead, we are focused on one thing: becoming the ultimate destination for developers who understand and need smart contract privacy.

We are building a network and set of tools that gives developers everything they need to build privacy-first apps with:

  • Anonymity by default
  • Private state read/write functionality
  • Private smart contract function execution

In this piece you’ll learn why privacy on account-based systems like the EVM doesn’t really work, why Aztec therefore isn’t EVM-compatible, and how Aztec makes dealing with the unique architecture of private state environments as intuitive as possible for smart contracts developers used to EVM-like environments.

Why do this at all?

Since day 1, Aztec Labs has pursued smart contract privacy: private compute that doesn’t rely on trusted third parties or trusted hardware security modules.

And in a world with fully on-chain smart contract privacy, private state has to be a first-class citizen.

That means no EVM, no Solidity, and no account-based blockchain architecture, all of which are privacy-leaking.

Privacy isn’t EVM-compatible

Now you might find yourself asking, “Wait, why doesn’t the EVM support privacy?” And in fact there have been Solidity smart contracts that run on the EVM and provide primitive, non-programmable privacy functionality like mixing.

But we’re not talking about that.

We’re talking about smart contract privacy — an entire system that incorporates programmable privacy within the contract itself — at the level of state variables and functions.

In Ethereum’s model, state variables are stored in a public account-based tree, and to edit one of those variables you need to broadcast to the world exactly which leaves of the tree you’d like to edit, what they contain, and how you’d like to edit them.

This has some drawbacks.

  • The current and historic values of every state variable are public
  • The functions invoked to execute state changes are public
  • The state variables modified by those functions are public

Et cetera.

UTXO’s and nullifiers, name a more iconic duo

Instead of this nakedly public way of doing things, Aztec relies on an encrypted UTXO (Unspent Transaction Object) data architecture — the same technology Bitcoin uses to store network state.

The foundation of Aztec’s privacy design is an append-only data tree containing encrypted UTXO’s and another data tree containing their nullifiers. And we owe the original UTXO-nullifier design to the pioneers who created the ZCash protocol.

UTXO’s are also referred to as “notes,” and we’ll refer to them as such for the rest of the piece.

For a layman’s explanation of our UTXO architecture, see this post.

In order to manipulate an owned note (which as a reminder are encrypted UTXO objects), users take the following steps:

  • A function is called
  • The function requests an edit to a private state
  • The function asks the user’s note database for all notes belonging to that private state
  • The user (in reality the user’s Aztec node) proves on their local machine that each of the retrieved notes exists as a leaf in the tree machine without revealing which leaf
  • The user does an action: read, change, or delete values inside the note
  • The user furnishes a nullifier, which prevents duplicate action and prevents the user from reading the same leaf ever again
  • The user inserts a new leaf, containing a new value, as a way of updating the private state’s value

A short history lesson

You can trace our obsession with notes back to our initial desire for smart contract privacy.

And one of the things “smart contract privacy” requires is hidden function inputs.

We started with zkSNARKs, which allow us to hide function inputs.

We then built Noir, an intuitive, open-source universal ZK language for writing functions whose inputs can be hidden. But Noir doesn’t have a built-in notion of state storage and state variables.

So now, we’re introducing a smart contract framework that creates state variable structs on top of Noir.

Let variables be variables!

So to have privacy, you need private state, and for private state you need private state variables.

But what are private state variables? Well they can’t be notes.

Notes stores data or information, and when combined with nullifiers they can preserve privacy, but notes are constant and immutable.

Variables are variable! They can be modified by the functions of a contract. So how can we create the concept of a private state variable using notes as a building block?

Well, as we saw above, notes can be destroyed and created. To create the abstraction of a private state variable, maybe we can cleverly destroy and create notes behind the scenes.

That’s exactly what Aztec does: declare a named private state variable, then write functions which read current state, edit that state, and write the updated state at the end.

Behind the scenes, these private state variable structs are figuring out:

  • which notes they need to gather as leaves in the private state tree
  • which notes they need to prove existence of in the tree
  • which notes they need to nullify
  • any new notes that need to be created and inserted into the tree

But to a developer, the variables just look like variables.

Private token contract example

To be less abstract, let’s think about the bread and butter of blockchain: a private token contract. The first thing a dev would wish to declare is a private_balance state variable.

Aztec allows a dev to declare a private_balance state variable, and then modify the balance in a transfer function.

Behind the scenes, the private_state struct that’s been exposed can figure out how to create and destroy notes in a way that represents adding-to or subtracting-from a user’s balance, all while not leaking that user’s balance (by emitting nullifiers from the function).

You can represent anything as a private state variable:

  • Values: an object with a value and owner field, like a banknote / $100 bill
  • NFTs: an object with a unique identifier, or that contains all the unique attributes of an NFT
  • Accounts: an object owned by one or many owners
  • and more! Votes, DeFi positions, identity objects, and anything else you can dream of

Private state variables store data or information, and can be programmed with two useful properties:

  • They can be mutable (updateable) or immutable (non-updateable); and
  • They can either comprise a single note (be a singleton) or comprise a group of notes describing a state variable (in this case a type of private state variable called a set)

It’s important to note (!) that notes are just used to store information, and don’t store functions or contracts. We will cover private and public execution in a future piece.

In case you can’t tell, managing UTXO’s would normally be a little bit complicated, and involves a few “gotchas” including how to:

  • Search the tree for one’s own notes efficiently
  • Combine notes
  • Make change from combined notes
  • Destroy and update notes with nullifiers

Unlike Ethereum accounts, which can simply be credited and debited, notes have to be created, combined, and nullified, which represents a distinctly different mental model. And where Ethereum values are just that — values — notes contain values.

Luckily, we at Aztec Labs have designed Aztec as a network with abstraction in mind. Our aim is to eliminate these difficulties and make writing Aztec smart contracts as similar to writing Ethereum smart contracts as possible.

Finally, while one of the benefits of our architecture is helping smart contract developers manage note complexity, one of the primary goals of this design is to abstract notes entirely from dApps.

Application developers rejoice! You’ll never have to think about UTXOs or notes at all, instead being able to call functions you would expect, like token.transfer(amount) or token.getBalance().

Passed around specific notes in an application would be extremely painful, and our smart contract framework helps abstract that completely from the dApp layer.

In the next post, we’ll cover Aztec’s smart contract framework and how it assists developers in managing private notes.

Start learning Noir today

Aztec Labs is a core contributor to Noir, the universal language of zero knowledge. We’re building an Aztec smart contract framework on top of Noir that extends its functionality beyond zk circuit writing language and toward private smart contracts.

Get started with Noir, read the docs, and get ahead of learning the prerequisites for building on Aztec.

Jump into the conversation

The Aztec Labs team is committed to building our privacy technology publicly. Bringing a fully decentralized L2 with smart contract privacy to market means there is plenty of debate about network design.

Join the conversation at discourse.aztec.network and participate in the design of Aztec’s network and economics.

Join our team

Aztec Labs is on the lookout for talented engineers, cryptographers, and business people to accelerate our vision of encrypted Ethereum.

If joining our mission to bring scalable privacy to Ethereum excites you, check out our open roles.

And continue the conversation with us on Twitter.

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Aztec Network
Aztec Network
7 Aug
xx min read

Alpha V5 Proving System Vulnerability

Status

Core contributors identified a critical vulnerability affecting the V5 Alpha proving system on 27 July 2026 through internal AI-assisted auditing.

V5 remains Alpha software. Critical findings can arise during this phase, and the audit process exists to identify them before broader deployment. This finding places V5 funds, applications, and contract state at risk.

Treat funds and applications on V5 as exposed to a protocol-level failure until contributors complete incident response work and operators carry out the required network actions.

What we are disclosing

An attacker may be able to exploit a flaw in the current V5 proving system by constructing a proof that passes verification for a transaction the network should reject. If accepted, that transaction could produce a state transition outside the rules V5 intends to enforce.

Contributors cannot determine whether anyone exploited the flaw before this finding. The affected system lacks the information needed to distinguish ordinary accepted transactions from transactions accepted through the flawed proving path. Historical chain activity cannot establish whether exploitation occurred or quantify its impact.

Application safeguards

We expect application teams to prepare safeguards in the coming weeks.

Those safeguards may include changes to application controls, deployment procedures, user flows, and migration plans. We expect each team to assess its contracts and determine which protections fit its architecture and users.

We expect teams planning a V5 deployment to pause that work until contributors publish further guidance. We expect teams with live contracts to review their ability to limit user exposure, isolate affected functionality, and move users to fresh deployments if needed.

We expect applications that maintain administrative or emergency controls to assess whether those controls can reduce user risk during the incident timeframe.

Next steps

Core contributors are working with operators, application teams, and bridge operators as applications add security guards around affected flows.

The findings from this incident will inform the V6 release, including circuit updates that prevent the network from accepting proofs tied to an affected proving system.

V5 launched as Alpha software, with V6 planned for later in 2026. Contributors will publish a security roadmap covering the remaining work and release path.

Known vulnerability status

Reviewers have not identified other high-severity or critical V5 Alpha vulnerabilities at this time.

Internal and external human audits have completed, and contributors continue AI-assisted auditing. Alpha is the period for identifying faults before production deployment.

Community
Community
4 Aug
xx min read

Dark Forest Aztec Game Goes Live

Dark Forest is a real-time strategy game played across a procedurally generated universe where most of the map is hidden. You cannot see rival players, their planets, or their fleets. You only know what you have explored. Everyone shares one universe, and nobody has the full picture.

In most onchain games, every position and every move is public, because the chain is public. Dark Forest used zero-knowledge proofs to break that assumption: players prove their moves are valid without revealing where those moves came from. The result is a game of hidden information running on a public network.

Dark Forest Aztec ports the original Dark Forest 0.6 to Aztec. It keeps the gameplay from the original and rebuilds the privacy layer on Aztec's programmable privacy.

A note before diving in: this is early, experimental software on Aztec Alpha V5. Treat it as an alpha and play accordingly.

The universe you cannot see

You start on a single home planet with almost the entire map dark. To find anything you mine the universe, running a client that explores coordinates and reveals what sits there: unclaimed planets, resources, and eventually the edges of other players' territory.

You are never handed a view of the board. You earn it one region at a time, and everyone else works under the same fog.

What is hidden on Aztec

Your home coordinates and your fleet movements are private state, expressed as first-class private notes on Aztec. Your location and where you send energy stay hidden, enforced in the contracts by zero-knowledge cryptography.

What sits onchain is a set of cryptographic commitments. Instead of storing every planet's full details in the open, the contracts store Poseidon2 hashes of entity state. When you make a move, your client supplies the full state, the contract checks it against the stored hash, applies the change under zero-knowledge constraints, and writes a new hash back. Full game state lives offchain and gets rebuilt from public logs by an indexer, which is what renders your map without exposing every player's position.

So you can prove you made a legal move from a planet you own without revealing where that planet is. Aztec applies the same principle to private payments and private contracts.

How you play

Four actions carry the game.

Explore. Your explorer sits in the bottom left. Set it running and it uncovers the map around you, surfacing planets, resources, and other players.

Send energy. Most planets produce energy. Click and drag from a planet you own toward a target to capture or weaken it.

Route silver. Asteroid fields produce silver. Move it to your planets and spend it on upgrades, or send it to a Spacetime Rip to convert it into score.

Hunt artifacts. Some planets hold artifacts. Your Gear ship discovers them. Once harvested, you deposit them on planets to boost stats.

Four stats drive most decisions.

Energy is the core resource. Planets generate it over time up to a capacity, and you spend it on everything: claiming planets, reinforcing your own, attacking rivals. Two details matter. Moves are taxed, so a flat percentage of a planet's total capacity burns every time you send energy, which discourages small frequent moves. And energy decays over distance, so send it too far and almost nothing arrives. A common rule of thumb is to let a planet fill to about 75%, then send it down to about 25%.

Defense reduces the damage incoming energy does when it lands. Higher-level planets often have lower defense, but they hold much more energy, so they still take more to capture. Defense matters most on front lines.

Range sets how far a planet can send energy. It governs how fast you expand and how efficiently you move energy inside your own empire, since shorter relative distances mean less decay. Good range also lets you strike deep into an opponent's territory.

Speed sets how quickly a move arrives. Usually secondary, though a fast strike can land before a rival reacts, and some playstyles reward capturing many nearby planets quickly.

Planets can also be upgraded with silver and enhanced with artifacts. Space types carry different multipliers, from mild Nebula to punishing Dead Space, so where a planet sits changes how it plays.

How scoring works

There is a scoreboard, and territory alone does not win it. This round scores two activities: discovering artifacts with your Gear ship, and withdrawing silver through Spacetime Rips.

Point values from the in-game help page:

  • Each unit of silver withdrawn: 1
  • Common artifact: 2,000
  • Rare: 10,000
  • Epic: 200,000
  • Legendary: 3,000,000
  • Mythic: 20,000,000

Silver accrues one point at a time. A single Mythic artifact is worth twenty million of them, so artifact hunting decides rounds and silver withdrawal sets your floor.

Silver has two competing uses. Spend it on upgrades and your planets get stronger, extending range and hardening defense. Withdraw it through a Spacetime Rip and it becomes scored points, but it is gone. Every unit is a choice between building the empire and banking points.

Upgrades tend to win early, since a stronger empire reaches more asteroid fields and finds more artifacts. Late in a round that calculation flips, because a planet you never use is worth less than points already scored.

Artifacts do both jobs at once. They score on discovery, and once deposited they boost a planet's stats, which makes the next expedition easier.

Why you explore

Nothing happens until you find something to act on. Your explorer turns dark space into planets you can capture, asteroid fields you can mine, and artifact-bearing planets you can raid. Sitting still means no new energy, no silver, no score.

Exploring also buys information. The map you have uncovered is an advantage nobody else holds. Knowing where high-level planets sit, which asteroid fields are unclaimed, and where space types shift lets you plan further ahead than someone still working through their starting region.

You find other players as a byproduct. There is no player list. You explore outward until your revealed region touches territory someone already owns: a planet in another player's colors, sitting where you were about to expand. Their home coordinates stay private, so you learn something narrow. Someone is here, roughly this direction, holding this much. You infer the rest, and you have no way of knowing whether they found you first.

What happens when you run into someone

You have three broad options.

Stay quiet and keep growing. Nothing forces you to engage. Keep exploring elsewhere, keep routing silver, keep upgrading. Your positions stay private, so silence costs you only time, which is what you want if they are stronger. The risk is that they are doing the same thing faster.

Fortify the border. If the contact sits somewhere you cannot lose, spend energy hardening the planets facing them. Defense is worth most where an attack will actually land. This keeps the option to fight without committing to one.

Attack. Send enough energy to overwhelm the target's defense and the planet becomes yours, along with its production and its position as a staging post. Higher-level planets are the prize and take proportionally more to crack.

Attacking costs more than energy. A move that lands tells your rival where you strike from, and that you are close enough to be worth answering. Retaliation can then come from directions you have not explored, launched from planets you cannot see.

Multiplayer in practice

Everyone plays one shared universe in real time. No turns, no lobbies. Energy regenerates whether you are watching or not, moves stay in flight while you sleep, and rivals expand while you are away from the screen.

Most strategy games let you watch a threat approach. Here you tend to see the consequences: a planet you owned this morning in someone else's colors, an incoming move you notice once it is already close.

That produces a particular kind of paranoia. You are trying to find everyone else while avoiding being found, and every expansion is a strategic bet that the space ahead is empty.

Information becomes tradeable, because it is scarce. Players compare notes, warn each other about aggressive neighbors, and agree who expands where, then break those agreements when the scoreboard makes it worth breaking.

Why it matters beyond the game

A fully onchain game where players cannot see each other's positions is hard to build, and building it well says something about the platform underneath.

Hidden state, private notes, and client-side proving are the same building blocks behind private applications across Aztec. Dark Forest is a way to watch them work.

Getting started

Dark Forest Aztec is playable now as an alpha. Expect a learning curve; the original was famous for it. DFArchon maintains onboarding material and a community for new players. Round One is live. The universe is dark, and everyone else is out there somewhere. Go find them, quietly.

Play Now

Follow the Builders

DFArchon on X

Source and docs

Aztec Network
Aztec Network
22 Jul
xx min read

How Gas Works on Aztec

Gas on Aztec

Gas on Aztec is known as Fee Juice and is used to pay for transaction costs. This is the same as $ETH on Ethereum. Some apps will handle transaction costs for you under the hood, but if you are using a browser extension wallet, you will not be able to send transactions without it. Fee Juice can be obtained by bridging the $AZTEC token on Ethereum to the Aztec Network L2. This means that under the hood, all activity that happens on Aztec is underpinned by the $AZTEC token bridged into the network. Some bridges like Shield (by human.tech) handle this for you, allowing you to allocate a portion of your bridged transaction to convert into Fee Juice and land in your wallet automatically.

Public vs Private Assets

Assets and transactions on the Aztec Network can be either public or private. If you bridge publicly, your tokens will arrive as public, traceable tokens visible to all. Privately bridging, on the other hand, will give you private assets that are visible only to you. These assets can then be sent privately to another user or wallet without ever revealing who you are, what tokens were sent, how many, or who the recipient is.

Public vs Private Gas

Like tokens on the Aztec Network, Fee Juice (gas) can also be public or private. The reason for this is that even if what you are sending is private, the gas you spend to execute that transaction could still be visible if you are using public Fee Juice, potentially revealing transaction patterns and activity. Private Fee Juice keeps your entire transaction footprint hidden. When you send a private transaction, you can use private Fee Juice, and when you send a public transaction, you can use public Fee Juice, which means your transaction costs are always aligned with the type of transaction you're making.

Fee Juice in Apps

Aztec has native fee abstraction, which means apps could let you pay for transactions in any token you want, or cover your fees entirely. Apps like Nyx may choose to cover part or all of a user's transaction costs, or allow you to pay in tokens that are convenient for you. This means you will most likely never see Fee Juice in an app; instead, you'll pay in whatever makes sense for what you're doing, on your terms. Similarly, you might never even see an Aztec wallet at all, because the app itself becomes your interface that you connect to using your MetaMask wallet.

Fee Juice in Browser Wallets

If you're using a browser extension like Azguard, you'll manage Fee Juice directly in your wallet alongside your private and public balances, converting between tokens as needed to cover transaction costs.

When you bridge tokens in, you'll need enough Fee Juice to cover the cost of your first transaction, then you'll need to monitor how much Fee Juice you have available to make transactions. Browser wallets will allow you to send either publicly or privately to other users and will default to using either public or private Fee Juice depending on the type of transaction. Both private Fee Juice and public Fee Juice will appear by default in your token list.

Wrapping up

How you handle Fee Juice depends on where you're transacting: apps can abstract it away entirely and let you pay in any token, while a browser wallet like Azguard puts it in your hands to manage across public and private balances. Match your gas to your transaction, keep private activity private down to the fee, and you move on your terms.

Aztec Network
Aztec Network
21 Jul
xx min read

Introducing Alpha V5

The Aztec Network today activated Alpha V5, a major protocol upgrade passed by token-holder governance and executed onchain. Alpha V5 reduces private-transaction proving times by more than 2x compared to the previous version, lowers the cost of a fully private transaction by roughly 50%, resolves the critical issues found in V4, and sees the first wave of apps go live. Users can now send private transactions and earn yield on Aave simply by connecting their Ethereum wallets on Nyx, bridge from Ethereum to Aztec using Shield or TRAIN, privately collect NFTs on RavenHouse, or play Dark Forest Aztec, a hidden-information strategy game in a universe that lives entirely onchain. 

"Alpha V5 continues Aztec's work at the frontier of client-side proving, with cryptographic breakthroughs that cut proving times by more than half this release," said Zac Williamson, Co-founder, Aztec Foundation. "We believe Aztec is now the fastest system in the world for proving a fully private transaction entirely on a user's own device, and every release moves the industry closer to private transactions at public transaction speeds."

As the only decentralized privacy L2, Aztec is the credibly neutral privacy layer for Ethereum. Aztec allows anyone to write smart contracts that include both private and public aspects – every private transaction is proven on the user's own device, so no operator, sequencer, or intermediary can see the data. The Alpha V5 proving improvements come from cryptographic advances that make this client-side proving faster than any prior release. The network remains in alpha, but with V5 it is ready for teams to begin building and deploying applications.

Performance - 2.5 second fully private transactions 

Making private transactions practical comes down to how quickly a proof can be generated on a user's own device, without offloading that work to a server that would learn what the user is doing. On Alpha V5, proving a private token transfer natively now takes approximately 2.5 seconds on a consumer laptop, down from 5.2 seconds on V4, and about 6.8 seconds in a browser, down from 12.5 seconds. Across every measured transaction flow, client-side proving times improved by approximately 2x compared with V4.

Bench machine: an M2 MacBook (12 cores, throttled to 8). "Native" runs Aztec's C++ proving binary; "WASM" runs the same prover in a browser engine (Node on V8).

Alpha V5 lowers ECDSA signature-verification cost by approximately 2x, speeds up Poseidon2 hashing by approximately 3x, and reduces the protocol circuit gate count by approximately 50% (gate count is the number of individual operations a proving circuit must perform, and it is the main driver of how long a proof takes to generate). Each of these lowers the amount of work a device performs to prove a transaction, and the reduction in gate count in particular compounds across every proof the network generates.

Apps - send, receive, and earn privately on Ethereum

Alpha V5 launches the first wave of apps on a network where privacy is built into the protocol rather than managed by an operator. On other networks that claim privacy, transactions still pass through an operator or node that reads them in plaintext, or depend on a viewing key that a third party holds, so users rely on someone else to protect their data and to decide when it gets disclosed. On Aztec, every private transaction is proven on the user's own device, so the app, the sequencer, and any operator never need to see the underlying data. Nyx is one of these apps, allowing users to privately send transactions and privately earn yield on Aave. 

"On Ethereum, everything you do is public. That's why we built Nyx: a private account governed by your Ethereum wallet", said Nikhil, Co-founder of Nyx. "Now you can send, receive and earn in private. Nyx was the first app live on the Aztec Alpha, and we're excited to expand participation to more users with the added stability of Alpha V5."

Other apps on Alpha V5 include Azguard and Nethermind (wallets), Shield, TRAIN, and RavenHouse (bridges), and the Aztecscan block explorers. Also launching is Dark Forest Aztec, a game where users explore a universe, control planets, manage planetary energy, expand territory, and launch attacks through strategic play with private state and hidden actions.

Dark Forest Aztec private universe-building gameplay

Lower costs, higher security 

Transaction fees on Aztec come from two main sources: the cost of proving a transaction and the cost of verifying the rollup proof on Ethereum. Alpha V5 reduces both. It lowers the network's proving-cost parameter by 50%, and it reduces the L1 gas required to verify a rollup proof by approximately 40%. Because rollup proofs are verified on Ethereum and that cost is shared across all transactions in a batch, the L1 reduction lowers fees for every user, while the lower proving-cost parameter reduces the per-transaction proving fee directly. Together, these bring the average cost of a fully private token transfer to under a $0.05 transaction cost.

Alpha V5 also hardens the network on several fronts. It resolves critical vulnerabilities found in Alpha V4 along with additional bugs discovered since launch. Aztec's bug bounty program on Cantina also drew more than 234 security researchers to participate. The network remains in alpha, and further bugs may surface as usage grows, but each release has closed the issues found in the last and strengthened the protocol against new ones. With the critical V4 issues resolved and these safeguards in place, Alpha V5 is stable enough for teams to begin building and deploying applications.

Availability

Alpha V5 is live now, view the Alpha V5 landing page for a full list of features, performance updates, and live apps to explore. 

About Aztec

Aztec is the only decentralized, privacy-first Layer 2 on Ethereum. Developers write private and public logic in the same smart contract, and private functions are executed and proven on the user's own device, so no operator sees the underlying data. The protocol is upgraded through onchain governance, and the network settles to Ethereum. For more information, visit aztec.network.