About Castelion

Castelion is bringing a new approach to defense development and production: one that focuses on short, iterative design cycles, rapid testing in development, and modern commercial manufacturing strategies for production at scale. Were designing, building, and testing next generation long range strike weapon systems to give America and its Allies a definitive edge and deter future conflicts.

Software Security Engineer

As a Software Security Engineer at Castelion, you will build and implement the cryptographic foundations that secure our flight systems. You will own encryption, code signing, secure boot, and key management across embedded platforms, ensuring the integrity, authenticity, and confidentiality of mission-critical systems.

You will work closely with embedded, avionics, and infrastructure engineers to integrate security directly into the full software and hardware stack from manufacturing provisioning through flight operations. We seek engineers who think in systems, understand threat models deeply, and can translate cryptographic principles into practical, resilient implementations in constrained environments.

Responsibilities

• Secure Boot & Root of Trust: Design and implement secure boot chains, hardware-backed root of trust mechanisms, and firmware verification processes for embedded flight systems.
• Cryptography & Encryption: Develop and integrate cryptographic protocols and libraries (e.g., symmetric/asymmetric encryption, key exchange, digital signatures) for embedded and distributed systems.
• Code Signing & Update Security: Own software signing infrastructure and verification workflows to ensure authenticity and integrity of firmware, flight software, and field updates.
• Key Management & Provisioning: Design secure key generation, storage, rotation, and provisioning systems across development, manufacturing, and deployed environments.
• Secure Communications: Implement and review authenticated and encrypted communication channels between vehicle, ground systems, and internal subsystems.
• Threat Modeling & Hardening: Conduct threat modeling and security reviews across the software stack. Identify vulnerabilities and implement practical mitigations aligned with mission constraints.
• Cross-Functional Integration: Partner with embedded, avionics, hardware, and infrastructure teams to embed security principles into system architecture from initial design through deployment.

Basic Qualifications

• Bachelors degree in Computer Science, Computer Engineering, Electrical Engineering, or related STEM field
• 3+ years of professional experience in software engineering with exposure to applied cryptography or security engineering