Senior Cryptography Engineer - C developper

As a Senior Cryptography Engineer at CryptoNext Security, you will take ownership of a key strategic project: porting our post-quantum cryptographic library across multiple platforms, with a particular focus on hardware/software FPGA accelerators. This role sits at the intersection of cryptography, low-level C engineering and embedded/hardware design, working within a Paris-based team building quantum-computer-resistant cryptography solutions.

What you'll do

• 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 optimize the CryptoNext Quantum Safe Library (C-QSL) across multiple platforms and architectures including x86, Arm, and RISC-V
• Adapt implementations for constrained and embedded environments such as IoT, Cortex-M, and embedded Linux
• Define and run test and validation strategies (functional, performance, security) across all target platforms
• Support security certification processes (CSPN, Common Criteria, FIPS) for the ported implementations
• Document your work through technical reports and, where relevant, scientific papers
• Collaborate closely with the R&D team and cross-functional teams to solve complex technical challenges
• Work on side-channel countermeasures and integration of the library with communication protocols and cryptographic objects (TLS, IPsec, PKCS#11, X.509) in post-quantum or hybrid mode, depending on your profile and product roadmap

What you bring

• Significant, senior-level experience in cryptography engineering (ideally 5+ years) gained in a software company or cybersecurity vendor, ideally with international teams or clients
• Engineering degree or Master's in computer science, mathematics or a related field
• Solid foundations in algorithmics and algebra, with the ability to translate mathematical constructs into efficient, correct implementations
• Strong programming skills in C with comfort working close to the hardware and optimizing for performance and security
• Comfort using embedded development and hardware debugging tools (GCC, GDB, QEMU, JTAG) and practical experience with source code management and continuous integration using GitLab CI
• Good French and English communication skills, both oral and written

Nice to have

• A PhD in cryptography or a related discipline
• Experience with public-key cryptography, symmetric-key cryptography, hash functions, and cryptographic protocols/frameworks such as OpenSSL
• Experience in embedded software development, hardware/software co-design, or FPGA implementation

What we offer

• Full-time position based in Paris
• Competitive salary, commensurate with experience
• Ownership of a strategic, high-impact technical challenge at the heart of our product roadmap

About CryptoNext Security

CryptoNext Security is a Paris-based start-up founded in 2019, specializing in quantum-computer-resistant cryptography. The company provides the Quantum Safe Remediation Suite, including the Quantum Safe Library (C-QSL), to help enterprises migrate to post-quantum cybersecurity. CryptoNext was cited among Gartner's 5 reference leaders in post-quantum cryptography and is a member of Campus Cyber, Hexatrust and Systematic.