Software Security Engineer

About the role

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.

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.

Requirements

• Bachelor's 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
• Experience implementing encryption, authentication, or digital signature systems in C, C++, Rust, or similar systems languages
• Strong understanding of cryptographic fundamentals (PKI, TLS, key exchange, hashing, signatures)
• Experience working in Linux-based or embedded environments
• To conform to U.S. Government export regulations, applicant must be a U.S. citizen or national, U.S. lawful permanent resident (green card holder), Refugee under 8 U.S.C.1157, or Asylee under 8 U.S.C.1158, or be eligible to obtain the required authorizations from the U.S. Department of State.

Skills

• Experience implementing secure boot or hardware root-of-trust mechanisms
• Experience with code signing pipelines and artifact verification
• Familiarity with TPMs, HSMs, or secure elements
• Experience in embedded, aerospace, defense, or other safety-critical systems
• Experience designing secure provisioning workflows in manufacturing environments
• Understanding of real-time systems and resource-constrained devices
• Experience with mTLS, certificate lifecycle management, and replay protection mechanisms
• Leadership qualities: Bias to Action and Creative Problem Solving; Desire and experience questioning assumptions leading to breakthrough ideas; Ability to bring applicable processes/concepts/materials from other industries for efficiency gains; Ability to personally resolve minor issues without significant support; High commitment and initiative; Passion for Castelion's mission; Ability to work in fast-paced, autonomous, demanding atmosphere; Strong sense of accountability and integrity; Clear communicator; Proactively communicates blockers; Trusted voice with regulators, suppliers, gate keepers and customers; Capable of tactfully managing stakeholder relationships; Logical, clear, detailed communication via email, IM, verbal.

Benefits

• Long-term stock incentives
• Comprehensive medical, vision, and dental insurance
• Four weeks of paid time off per year