Senior Cryptography Engineer - C developper

CryptoNext Security; Paris; Hybrid; EUR 90,000 - 130,000; Full time

Benefits offered by this job

Ownership of strategic project

Global high-growth startup

Based in Paris

Job summary

CryptoNext Security in Paris seeks a senior Cryptography R&D Engineer to port the Quantum Safe Library across platforms and accelerators. You will work at the intersection of cryptography, low-level C, and embedded hardware, delivering high-performance, secure implementations.

You will collaborate with international teams, drive test strategies, and contribute to certifications while advancing post-quantum technology on multiple architectures and OS targets.

Qualifications

• Significant senior cryptography engineering experience in software or hardware contexts.
• Strong programming in C with low-level optimization skills.
• Experience porting libraries across platforms and validating security properties.
• Fluency in French and English, written and spoken.

Responsibilities

• Design and implement efficient C code for post-quantum algorithms with emphasis on performance and security.
• Port the CryptoNext Quantum Safe Library (C-QSL) across platforms and architectures.
• Adapt implementations for constrained embedded environments (IoT, Cortex-M, embedded Linux).
• Define tests and validation strategies for functional, performance, and security aspects.
• Support security certifications (CSPN, Common Criteria, FIPS) for ports.
• Document work through technical reports and occasional scientific papers.

Skills

Cryptography engineering

C programming

Embedded systems

Low-level optimization

OpenSSL experience

French & English comms

Education

Engineering degree or Master’s in CS/Math

PhD in Cryptography (strong plus)

Tools

GCC

GDB

QEMU

JTAG

GitLab CI

Job description

Who we are

CryptoNext Security is a Paris-based start-up founded in 2019, building on more than 20 years of academic research. CryptoNext is a software vendor specializing in quantum-computer-resistant cryptography (PQC: post-quantum cryptography). Its software suite, the Quantum Safe Remediation Suite, includes the world-reference Quantum Safe Library (C-QSL), covering the full selection of NIST algorithms, and helps enterprises and integrators migrate to the era of post-quantum cybersecurity.

CryptoNext Security was cited among the 5 reference leaders in Gartner’s report on post-quantum cryptography (October 2021) and received the Innovation Prize at «Les Assises 2022». CryptoNext is a member of Campus Cyber, Hexatrust and Systematic, and was selected in 2022 to join a workgroup of the US National Cybersecurity Center of Excellence (NCCoE) dedicated to PQC migration best practices.

We are looking for a highly motivated, senior Cryptography R&D Engineer to join our team and 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.

On a daily basis, you will

• 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


• Adapt implementations for constrained and embedded environments (e.g., IoT, Cortex-M, 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.

The CryptoNext Quantum Safe Library is developed mainly in C and Assembly, targeting several operating systems (Linux, Windows, iOS, Android…) and processor architectures (x86, Arm, RISC-V…), as well as FPGA-based hardware accelerators.

Other tasks may include, depending on your profile and the product roadmap: work on side-channel countermeasures, and collaboration with the team in charge of integrating the library with communication protocols and cryptographic objects (TLS, IPsec, PKCS#11, X.509…) in post-quantum or hybrid mode.

The skills you will demonstrate

• Significant, senior-level experience in cryptography engineering, ideally 5+ years, gained in a software company or department of a larger organization (cybersecurity vendor, IT application or hardware provider), ideally with international teams or clients.


• Engineering degree or Master’s in computer science, mathematics or a related field; a PhD in cryptography or a related discipline is a strong plus.


• Solid foundations in algorithmics and algebra, with the ability to translate mathematical constructs into efficient, correct implementations.


• Strong programming skills in C; 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.


• Experience with public-key cryptography, symmetric-key cryptography, hash functions, and cryptographic protocols/frameworks such as OpenSSL is a plus.


• Experience in one or more of the following is a strong plus: embedded software development, hardware/software co-design, FPGA implementation.


• Good French & English communication skills, both oral and written.

What's in it for you at CryptoNext

• Ownership of a strategic, high-impact technical challenge — multi-platform porting and hardware acceleration — at the heart of our product roadmap.


• A fast-growing, globally recognized deep-tech start-up, named among Gartner’s 5 reference leaders in post-quantum cryptography.


• Full-time position, based in Paris.


• Competitive salary, commensurate with experience.