Principal Software Engineer

  • Paris
  • Full-Time
  • Start Date: 02 May 2021
  • Apply Now


Established in 2020, Xkey is a cybersecurity startup operating within decentralized finance (DeFi). From our office in Paris, we are building an API for digital asset security. More specifically, Xkey provides safe, cloud-native custody as a service to help companies secure cryptos & tokens.

Xkey is also a stellar team of 8 pioneers incubated at Station F (the world's biggest startup campus), the Garage (#1 blockchain ecosystem in Europe), and Techstars Future of Finance in collaboration with ABN AMRO.

Job Description

As Principal Engineer, you will be leading the product architecture & development on multiple fronts.

You will contribute to the execution of one of the most ambitious tech projects in Europe right now: building a security standard for a trillion-dollar crypto industry.

You will join an amazing team of leaders (Chief Technology Officer, Chief Science Officer, Cryptographers, Engineers, etc.), in a highly challenging and collaborative environment.


Your primary goal will be to take the product through the full release life cycle from its initial development (Alpha, Beta, RC) to the scaling phases (RTW, General Availability).

Your primary metric will be WTL (Weeks to Launch).

Concretely, here are the tasks to be expected:

  • Share the big picture to your team, define the levels of priority within the product roadmap, and be accountable for the deadlines and the quality of production.
  • Act as a powerhouse of ideas on all technical issues (ops, security, architecture, stack, etc.).
  • Ensure scalability and high availability of the product, as well as top-notch code quality.
  • Build, operate, and ensure the security of the product, namely the API and the network.
  • Implement an MPC-based crypto-system with the assistance of our Chief Science Officer
  • Set up white hacking sessions with the Head of Security and the science team to prepare for major cybersecurity & cryptology audits from a Big Four and other specialized agencies.
  • Facilitate cross-branch communication and know-how exchange between team members.
  • Implement technical best practices and new ideas to encourage innovation within your team.
  • Work closely with the CTO and UI/UX team to transform feedback into features.
  • Work closely with the Head of Security to embed best-in-class InfoSec (DevOps/SecOps) processes within the service architecture and the internal workflows.
  • Work closely with the Head of Legal and the compliance team in charge of crunching our legal requirements to translate the product evolutions into features that take into account jurisdictional constraints and regulatory frameworks from the scratch.
  • Occasionally participate in client meetings to help them better benchmark our solution against market alternatives.
  • Be part of weekly meetings to discuss strategy with the CEO and other team leaders.
  • Keep abreast of the latest developments in crypto, DeFi and blockchain to feed the company's strategic orientations.


  • Role: Principal Engineer (possibility to evolve as Head of X)
  • Salary: €80-120K / year (+ post-investment raise + competitive YoY increase)
  • Equity: 0.1-2.0% (≈ €1-20M in 2-4 years, dilution included)
  • Location: Work from home 100% remote, in London, or Paris HQ.
  • Paid vacation: >5 weeks off / year
  • Employee benefits: transportation, perks, events, insurance, meals, office space...

Preferred Experience


  • 7+ years of experience as software engineer
  • Engineering expert capable of challenging the reasoning of other engineers.
  • Profound experience in designing and developing secure RESTful APIs.
  • You should be very good in one of them, and be willing to learn another one: Rust, Go, TypeScript.
  • Experience in writing Unit Tests, Integration Tests, End-to-end tests, performance tests, chaos engineering.
  • SQL (PostgreSQL) and NoSQL (whatever suits for particular job) databases.
  • Experience with one of AWS, MS Azure, or GCP.
  • Experience building Continuous Delivery pipelines, 12-Factor App, understanding how to build domain-driven micro-services.
  • Functional and Object-Oriented Programming. We will ask you to implement Reduce and Curry in one of the interviews.
  • Must have experience with two of the following infrastructure technologies: Terraform, Ansible, Kubernetes, Nomad.
  • Optionally and Ideally:
    • Understanding of Functional Programming, Object-Oriented, and Logical Programming.
    • No fanboy-ism in agile methodologies.
    • Experience in building observable systems, with Kibana, Grafana, Splunk, Prometheus, Datadog, etc.
    • Knowledge of information security management systems and relevant industry standards (ISO, etc.)
  • Experience building secure, fault-tolerant, and resilient systems.
  • Founding-spirited with grit & guts to pursue complex worldwide ambitions.
  • Self-starting, result-and-solution-oriented entrepreneur.
  • Problem-solving competences in respect to other stakeholders.
  • Humble, respectful, and very professional to others.
  • Able to decide even in stressful, unstable situations.
  • Big appetite for Cybersecurity, Fintech, Blockchain and/or Crypto space.
  • Fluent English language skills (written/spoken).
  • (Bonus) Experience working with cryptocurrencies, integrating networks, creating smart contracts.
  • (Bonus) Working with public and private blockchain implementations
  • (Bonus) Experience integrating or developing DeFi protocols.
  • (Bonus) Experience building distributed, federated, or peer-to-peer decentralised systems.

Recruitment Process

  • 30mn screening interview with Christopher and David
  • 60mn focus interview with David and Houda
  • 60mn technical testing with David
  • 60mn who interview with Clarisse, Christopher, Houda, and David

Additional Information

  • Contract Type: Full-Time
  • Start Date: 02 May 2021
  • Location: Paris, France (75013)
  • Experience: > 7 years
  • Possible full remote
  • Salary: between 80000€ and 120000€ / year