Zama Builder Stories #1 - Five Years With FHE

May 6, 2026

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The Zama Team

‍Builder Stories is a Zama series profiling the developers building confidential applications on the Zama Protocol.

The winners from Zama Developer Program Mainnet Season 1, Patricia Ortuño Otero and Joaquin Trujillo, sharing their builder journey with Zama Protocol, and introducing their winning project of Confidential Onchain Payroll system.

From FHE Research to a Production Use Case

In 2021, Patricia Ortuño Otero first learned about Fully Homomorphic Encryption as a student. After research and study, she chose FHE as her final-year telecommunications project which won a university award in defence and security; her master's thesis, an FHE arithmetic logic unit in Rust on top of TFHE-rs, won two more.

Five years later, with co-founder Joaquin Trujillo, she won the Special Bounty track of the Zama Developer Program Mainnet Season 1 with Paychain, a non-custodial, GDPR-compliant payroll system that runs entirely on encrypted data, end to end, on a public chain.

Most teams winning the Zama Developer Program are exposed to FHE for the first time. Patricia has been watching Zama since the original TFHE library.

Meet the team.

Patricia describes herself as a developer of deep tech and secure infrastructure for when off-the-shelf solutions aren't up to the job. Her work spans cloud, embedded systems, networking, and full-stack development.

Joaquin came into web3 through her, and Paychain is their first major build together. He owns the implementation and the UI/UX. "Ever since I met Patricia, I haven't stopped learning," he says. "She has an impressive ability to see what people need, and the skill to scale and design highly complex system architectures."

Why payroll needs confidentiality.

Of every possible use case for confidential finance, payroll is one of the clearest where confidentiality is not optional, and one of the most stuck.

The options before Paychain were suboptimal. Run payroll on a public chain and broadcast every salary to anyone with Etherscan. Move to a private chain and take on running validators, permissioning, and hardened cloud, with a weaker trust model. Or hand it to a custodial provider and reintroduce a third party.

"Public blockchains are transparent by default," Patricia says. "It does give you auditability, but this is not acceptable when paying your employees."

How Paychain works.

In plaintext: the operator uses confidential ERC-7984 tokens to pay employees, so balances and salaries move onchain without exposing the amounts. Smart contracts run the payroll rules without ever decrypting them. Onchain, the system exposes only random identifiers and encrypted payroll logic. Personal data about the company and its employees lives off-chain, protected with a separate layer of static encryption and periodic key rotation.

This is the architecture FHE was made for. Computation happens directly on encrypted data. The chain verifies and executes; the network never sees what was paid.

The click moment was realising that confidentiality and public-chain verifiability were not mutually exclusive.
— Joaquin Trujillo

The lesson behind it: Design from the start around what must stay hidden, which operations need that data, and who can decrypt the result. That mindset also aligns naturally with GDPR's push toward data minimisation by default.

Live demo: paychain-on-chain-payroll-web.vercel.app
Code base: github.com/patriciaOrtuno28/Paychain-On-Chain-Payroll

Watching Zama grow up.

Patricia is one of the few builders in this season's program who can draw a five-year line through Zama's history since 2021. Her view on what's changed:

Zama hasn't remained merely a GitHub repository. It has evolved into something much bigger: the creation of a complete ecosystem that includes building community loyalty.
— Patricia Ortuño Otero

Back when she started researching FHE, she was wrestling with deep knowledge of cryptography such as BGV and BFV schemes and the noise budget of multiplications. "I never would have imagined that I'd end up seeing its real-world applications in distributed ledger technology."

The Real Challenge Wasn’t Cryptography

What surprised Joaquin most about building with FHE is that the hardest problem sits upstream of the code. "You no longer see data, you can't debug as usual, and every operation has a cost." You learn to design a system you'll never inspect at runtime.

The actual hard part was legal architecture: deciding what data must be decryptable, who's allowed to decrypt it, and how to manage permissions without breaking the product. "The most challenging part is no longer the technical side, but rather legal and data protection."

Advice for Developers Building with FHE

For developers who want to build confidential applications using Zama Protocol or interested in the Zama Developer Program, here are their advices:‍

Joaquin, on building your first project with the Zama Protocol:

Don't try to adapt a traditional system to FHEVM. You have to design it from the ground up as if you'll never know the data. A major mistake is to think in the clear and then encrypt, which goes against the very nature of FHE. Focus on what must remain hidden, define which operations require that data, and determine who can decrypt the result.

Patricia, on joining the Zama Developer Program:

Most developers, out of habit or client requirements, build the same kind of applications over and over: the same front-ends, the same back-end patterns, the same smart contracts. Ever since AI became our programming co-pilot, we haven't faced a real challenge. We give instructions like automatons. This program encourages you to dust off your creativity. It pushes you to tackle a new design space, where privacy, cryptography and application logic interact in ways most developers never get the chance to explore.
Don't you miss wrestling with a bug on your own?

Building the Next Generation of Confidential Applications

Paychain is not trying to reinvent finance overnight. Instead, the team hopes to demonstrate that FHE is no longer experimental research, but a practical technology capable of powering real applications today.

“Our aim is to demonstrate that FHE has real-world applications.”

For Patricia, success means:

more developers learning about FHE
more products built with it
and a stronger ecosystem around confidential computing

Want to learn more? Reach out to the builders:

Patricia Ortuño Otero: LinkedIn‍
Joaquin Trujillo: LinkedIn

Build with Zama.

‍Patricia and Joaquin each summed up their journey with Zama in a single line:

Joaquin: "Learning about a tool I found quite interesting and would like to use more going forward."

Patricia: "My journey with Zama has been about watching a project I've been following for five years grow, and finally seeing what I always hoped would come to fruition: actual products."

The Zama Developer Program is designed to support builders at every stage, from experimentation to production-ready projects. Each season, we rewards builders to demonstrate real-world use cases with Zama Protocol.

Join the program →

Additional Links

Need help? developer@zama.org

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Privacy is necessary for an open society in the electronic age. Privacy is not secrecy. A private matter is something one doesn't want the whole world to know, but a secret matter is something one doesn't want anybody to know. Privacy is the power to selectively reveal oneself to the world.If two parties have some sort of dealings, then each has a memory of their interaction. Each party can speak about their own memory of this; how could anyone prevent it? One could pass laws against it, but the freedom of speech, even more than privacy, is fundamental to an open society; we seek not to restrict any speech at all. If many parties speak together in the same forum, each can speak to all the others and aggregate together knowledge about individuals and other parties. The power of electronic communications has enabled such group speech, and it will not go away merely because we might want it to.Since we desire privacy, we must ensure that each party to a transaction have knowledge only of that which is directly necessary for that transaction. Since any information can be spoken of, we must ensure that we reveal as little as possible. In most cases personal identity is not salient. When I purchase a magazine at a store and hand cash to the clerk, there is no need to know who I am. When I ask my electronic mail provider to send and receive messages, my provider need not know to whom I am speaking or what I am saying or what others are saying to me; my provider only need know how to get the message there and how much I owe them in fees. When my identity is revealed by the underlying mechanism of the transaction, I have no privacy. I cannot here selectively reveal myself; I must always reveal myself.Therefore, privacy in an open society requires anonymous transaction systems. Until now, cash has been the primary such system. An anonymous transaction system is not a secret transaction system. An anonymous system empowers individuals to reveal their identity when desired and only when desired; this is the essence of privacy.Privacy in an open society also requires cryptography. If I say something, I want it heard only by those for whom I intend it. If the content of my speech is available to the world, I have no privacy. To encrypt is to indicate the desire for privacy, and to encrypt with weak cryptography is to indicate not too much desire for privacy. Furthermore, to reveal one's identity with assurance when the default is anonymity requires the cryptographic signature.We cannot expect governments, corporations, or other large, faceless organizations to grant us privacy out of their beneficence. It is to their advantage to speak of us, and we should expect that they will speak. To try to prevent their speech is to fight against the realities of information. Information does not just want to be free, it longs to be free. Information expands to fill the available storage space. Information is Rumor's younger, stronger cousin; Information is fleeter of foot, has more eyes, knows more, and understands less than Rumor.We must defend our own privacy if we expect to have any. We must come together and create systems which allow anonymous transactions to take place. People have been defending their own privacy for centuries with whispers, darkness, envelopes, closed doors, secret handshakes, and couriers. The technologies of the past did not allow for strong privacy, but electronic technologies do.We the Cypherpunks are dedicated to building anonymous systems. We are defending our privacy with cryptography, with anonymous mail forwarding systems, with digital signatures, and with electronic money.Cypherpunks write code. We know that someone has to write software to defend privacy, and since we can't get privacy unless we all do, we're going to write it. We publish our code so that our fellow Cypherpunks may practice and play with it. Our code is free for all to use, worldwide. We don't much care if you don't approve of the software we write. We know that software can't be destroyed and that a widely dispersed system can't be shut down.Cypherpunks deplore regulations on cryptography, for encryption is fundamentally a private act. The act of encryption, in fact, removes information from the public realm. Even laws against cryptography reach only so far as a nation's border and the arm of its violence. Cryptography will ineluctably spread over the whole globe, and with it the anonymous transactions systems that it makes possible.For privacy to be widespread it must be part of a social contract. People must come and together deploy these systems for the common good. Privacy only extends so far as the cooperation of one's fellows in society. We the Cypherpunks seek your questions and your concerns and hope we may engage you so that we do not deceive ourselves. We will not, however, be moved out of our course because some may disagree with our goals.The Cypherpunks are actively engaged in making the networks safer for privacy. Let us proceed together apace.Onward.Eric Hughes9 March 1993