Welcome Steffel Fenix

We’re excited to announce that Steffel Fenix has joined Dfns as a Senior Blockchain Engineer. Steffel brings a rare combination of deep smart contract expertise, hands-on security experience, and a strong background in distributed systems. His work spans from building DeFi primitives to actively defending blockchain systems against sophisticated adversaries, with a consistent focus on security, correctness, and performance.

From DeFi protocols to adversarial security

Before joining Dfns, Steffel worked as an independent smart contract auditor, where he focused on securing some of the most widely used protocols in DeFi. His work included audits for projects such as Curve, Yearn, Euler, and Olympus, where the stakes are not theoretical but measured in billions of dollars of onchain value.

Beyond traditional audits, Steffel has been involved in active defense against state-sponsored attackers. This type of work goes far beyond reviewing code. It requires understanding attacker behavior, anticipating exploit patterns, and designing systems that remain secure under real-world adversarial conditions. His approach combines deep technical analysis with practical mitigation strategies, ensuring that vulnerabilities are not only identified but effectively neutralized.

Building core DeFi infrastructure

Earlier in his career, Steffel was a smart contract developer at Yearn Finance, where he contributed to the development of v2 and v3 vaults. These systems are at the core of DeFi’s yield generation mechanisms and require careful design to balance composability, efficiency, and security.

His work focused on improving contract efficiency, reducing gas costs, and strengthening security guarantees. These optimizations are not incremental. In a system where every transaction is executed onchain, even small improvements can have a significant impact on scalability and user experience.

He also worked closely with cross-functional teams to bring new DeFi products to market, ensuring that contracts were not only secure in isolation but also integrated correctly within broader protocol architectures.

A systems-oriented engineering background

Steffel’s experience extends beyond smart contracts into broader system design and backend engineering. At Nash, he worked on secure multi-party computation systems, contributing to the development of cryptographic protocols that strengthen platform security. He also led efforts to migrate backend systems to GraphQL, improving scalability and performance.

Earlier, at Crypto.com, he led engineering teams and helped establish development standards, improve workflows, and scale internal systems. His work combined hands-on technical contributions with team leadership and operational improvements.

He began his career building and scaling distributed systems across different industries, from marketing automation platforms handling millions of users to high-performance web applications. This foundation gives him a strong understanding of how blockchain systems interact with real-world infrastructure.

What Steffel will build at Dfns

At Dfns, Steffel will focus on strengthening the smart contract and blockchain execution layers of the platform, bringing a security-first mindset shaped by years of adversarial experience. 

He will contribute to the design and auditing of onchain components that interact with Dfns wallets, ensuring that integrations with DeFi protocols, staking systems, and token standards are robust and secure. This includes reviewing contract logic, identifying edge cases, and ensuring safe interaction patterns across a wide range of protocols.

Beyond contracts, Steffel will work on transaction execution flows that bridge off-chain systems with onchain actions. This requires ensuring that every transaction constructed, signed, and broadcasted behaves exactly as intended, even in the presence of network inconsistencies, MEV dynamics, or unexpected contract behaviors.

Security will remain a central focus. Steffel will help reinforce Dfns’ approach to threat modeling, vulnerability detection, and mitigation strategies across both onchain and off-chain components. His experience with real-world attacks will directly inform how systems are designed and hardened.

Finally, he will contribute to improving how developers and institutions interact with blockchain systems through Dfns. This includes making complex DeFi interactions safer, more predictable, and easier to integrate into financial workflows.

We are building infrastructure that financial institutions rely on to interact with blockchains in a secure and controlled way. This requires deep expertise across both onchain and off-chain systems, as well as a clear understanding of how things break in practice. Steffel brings exactly that.

We’re excited to have him on board.

We’re hiring

Dfns continues to grow across engineering, product, and operations. If you’re interested in building infrastructure for the next generation of financial systems, we’d love to hear from you.

Apply here: jobs.deel.com/job-boards/dfns