Senior Software Engineer

About Certonymity Certonymity is building the next generation of secure communication. Our mission is to make email encryption simple and accessible— combining advanced cryptography with real-world identity verification. Our first product, C.Email, allows users to send and receive end-to-end encrypted emails without relying on third parties or complex setups. Each user has a verified digital identity, linked to their real-world passport but kept fully private through cryptographic keys — ensuring anonymity with accountability. We're an ambitious, self-financed start-up with our founders having an entrepreneurial background in AI, Hedge Funds, Biotech and Energy Production. We are headquartered in London with our technical team based across the UK and France. Operating independently allows us to move quickly, innovate freely, and stay focused on our mission to build cutting-edge cryptographic, blockchain, and mobile-first privacy technology. About the Role We're looking for a Senior React Native Engineer to play a key role in building, improving, and scaling our encrypted email app, C.Email. You'll work closely with our CTO, cryptography specialist, and engineers to deliver a high-performing, secure, and intuitive product. This is a hands-on engineering role with end-to-end ownership — from development and testing to deployment and user experience improvements. You'll be instrumental in shaping how millions of users communicate securely. Responsibilities Lead core development of new features from concept to release, owning them end-to-end — from design discussions and prototyping through to testing and deployment. Develop and enhance the C.Email mobile app using React Native (Expo + CNG). Improve app stability and performance; resolve bugs and UI issues. Implement cryptography improvements for performance and integration. Write modular, testable, maintainable code with clear documentation. Build and own automated testing frameworks (unit, component, and user simulation). Collaborate with blockchain engineers on integration for data backup and key management systems. Participate in daily stand-ups and code reviews, sharing best practices and ideas. Qualifications Strong experience in software engineering with React Native and TypeScript. Experience setting up automated tests from scratch — unit, component, and user-simulation tests. Strong understanding of mobile-first architecture (local data storage, offline-first). Experience working in startups or small technical teams (series A or B/ pre VC funding). Proven ability to take end-to-end ownership of a product area or feature. Experience working with email standards and protocols (e.g. MIME, Gmail API) is a plus. Required Skills React Native (Expo) – advanced development and optimisation. TypeScript / JavaScript – daily use and strong understanding. Kotlin / Swift – for native components. Go – used for cryptography. C++ – for performance improvements and interface integration (secondary priority). GCP / AWS (light) – basic infrastructure setup and management (SES, AWS lambda, Redis, RDS, EC2 autoscaling). Familiarity with cryptographic principles (key exchange, signing, encryption). Preferred Skills Experience working with email standards and protocols (e.g. MIME, Gmail API) is a plus. What's Next? Talent Acquisition Interview (30-45 minutes) - initial screen to tell you about Certonymity's mission and get to know you more. Practical coding exercise (60-90 minutes) - we'll send you a task to complete during a live coding interview with our CTO and one of our Senior Software Engineers. Final Stage Interview (30 minutes) - you'll get to meet with our CEO and founder and explore more about the role with the company.