Senior Cryptography Engineer - C developper

CryptoNext Security SAS; Paris; On-site; EUR 90,000 - 130,000; Full time

Benefits offered by this job

Ownership of strategic challenge

Global PQC recognition

Paris-based role

Competitive salary

Job summary

CryptoNext Security SAS in Paris is seeking a senior Cryptography R&D Engineer to lead porting of the Quantum Safe Library across platforms and hardware accelerators. You will design efficient C code for post-quantum algorithms, optimize for performance and security, and work close to hardware with embedded Linux, Cortex-M, and FPGA targets.

You bring 5+ years in cryptography engineering, a degree in CS/math (PhD a plus), strong C skills, and experience with GCC, GDB, QEMU, JTAG, and OpenSSL.

Qualifications

• Significant, senior-level experience in cryptography engineering (5+ years).
• Engineering degree or Master's in computer science, mathematics or a related field; a PhD in cryptography is a strong plus.
• Strong foundations in algorithmics and algebra with the ability to translate mathematical constructs into efficient implementations.
• Strong programming skills in C; comfortable working close to hardware and optimizing for performance and security.
• Experience with embedded development and hardware debugging tools (GCC, GDB, QEMU, JTAG) and CI with GitLab CI.
• Experience with public-key cryptography, symmetric-key cryptography, hash functions, and cryptographic protocols/frameworks such as OpenSSL is a plus.
• Experience in embedded software development, hardware/software co-design, FPGA implementation.
• Good French & English communication skills, both oral and written.

Responsibilities

• Design and implement efficient C code for post-quantum cryptographic algorithms, 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.

Skills

Cryptography engineering

C programming

Embedded development

Hardware debugging tools

GitLab CI

OpenSSL knowledge

Public-key cryptography

French & English skills

Education

Engineering or Master's in CS/Math

PhD in cryptography (strong plus)

Tools

GCC

GDB

QEMU

JTAG

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.