Welcome Sébastien Geay

We’re excited to welcome Sébastien to Dfns as our new Senior Core Systems Engineer. Sébastien brings more than 18 years of experience designing and building distributed systems, backend platforms, and production-grade software. From early R&D environments to large-scale SaaS systems, his work consistently reflects the same principles: clear architecture, strong data modeling, high reliability, and iterative delivery. That mindset aligns perfectly with how we build at Dfns.

Deep expertise in cryptographic infrastructure

Before joining Dfns, Sébastien was a Staff Software Engineer at SandboxAQ, following its acquisition of Cryptosense, where he worked on two generations of SaaS platforms focused on Cryptographic Lifecycle Management (CLM). His work included:

• Designing systems for continuous inventory of keys, certificates, secrets, and non-human identities
• Building APIs and connectors for cryptographic cartography and vulnerability detection
• Supporting post-quantum cryptography readiness
• Leading a full migration of a legacy OCaml file system scanner to a high-performance Rust implementation

This blend of cryptography, data modeling, and large-scale distributed systems is directly relevant to the core infrastructure we operate at Dfns. We are not building dashboards. We are building critical infrastructure for wallet orchestration, policy enforcement, and secure key operations across regulated financial environments. That requires engineers who think in systems, not features.

A strong foundation in distributed SaaS systems

Earlier in his career, Sébastien led the design and development of unified SaaS platforms for IT supervision and cybersecurity, integrating monitoring, automation, and billing into cohesive production systems. He has worked across a broad technical stack (Rust, Python, Java, Kafka, PostgreSQL, GraphQL, REST, cloud infrastructure) always with a focus on architecture clarity and long-term maintainability. That architectural discipline is essential for Dfns as we continue to scale:

• Multi-tenant wallet infrastructure
• Policy engines and entitlement systems
• High-throughput API layers
• Auditability and compliance-grade logging
• Distributed signing and orchestration workflows

From game engines to financial infrastructure

Earlier in his career, Sébastien worked on game engines and R&D systems, leading engine and tooling teams and building multi-platform architectures. While far removed from finance, that experience forged a strong foundation in performance engineering, tooling, and systems design. The common thread throughout his career is clear: complex systems, built carefully, shipped iteratively.

As Senior Core Systems Engineer, Sébastien will focus on strengthening the foundations of our wallet and orchestration platform: backend architecture, data modeling, performance, and long-term scalability. As institutional demand for secure digital asset infrastructure grows, the expectations around reliability, compliance, and clarity grow with it. We are investing deeply in our core systems to meet that standard.

Sébastien’s experience in cryptographic lifecycle management, distributed systems, and large-scale SaaS platforms makes him a strong addition to that mission. Welcome to Dfns, Sébastien.

We’re hiring! jobs.deel.com/job-boards/dfns