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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.
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.
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."
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?
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:
Want to learn more? Reach out to the builders:
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.
Need help? developer@zama.org
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