Senior Cryptography Engineer - C Developer

About the role

CryptoNext Security is a Paris-based start-up founded in 2019, building on more than 20 years of academic research, that develops quantum-computer-resistant cryptography (post-quantum cryptography). It is looking for a senior cryptography R&D engineer to own a key strategic project: porting its post-quantum cryptographic library across multiple platforms, with a focus on FPGA hardware accelerators. The role combines cryptography, low-level C engineering and embedded/hardware design.

Key responsibilities

• Design and implement efficient C code for post-quantum cryptographic algorithms (NIST-selected or recommended by EU agencies), balancing performance, portability and security.
• Port and optimise the CryptoNext Quantum Safe Library (C-QSL) across multiple platforms and architectures.
• Adapt implementations for constrained and embedded environments (IoT, Cortex-M, embedded Linux).
• Define and run functional, performance and security tests and validation across all target platforms.
• Support security certification processes (CSPN, Common Criteria, FIPS) for the ported implementations.
• Document work through technical reports and, where relevant, scientific papers.
• Collaborate with the R&D team and cross-functional teams; other tasks may include side-channel countermeasures and integration with TLS, IPsec, PKCS#11 and X.509.

Required profile

• Significant senior-level cryptography engineering experience, ideally 5+ years, in a software company or a large organisation (cybersecurity vendor, IT application or hardware provider), ideally with international teams or clients.
• Degree or Master's in computer science, mathematics or a related field; a PhD in cryptography or a related discipline is a strong plus.
• Good French and English, spoken and written.

Required skills

• Solid foundations in algorithmics and algebra, able to turn mathematical constructs into efficient, correct implementations.
• Strong C programming, close to the hardware, with embedded debugging tools (GCC, GDB, QEMU, JTAG) and GitLab CI.
• Public-key, symmetric-key cryptography, hash functions and frameworks such as OpenSSL are a plus; embedded software, hardware/software co-design and FPGA implementation are strong pluses.

What we offer

• A full-time position in Paris.
• Ownership of a strategic, high-impact technical challenge at the heart of the product roadmap.
• A fast-growing, globally recognised deep-tech start-up named among Gartner's 5 reference leaders in post-quantum cryptography.
• Competitive salary commensurate with experience.