Senior Software Engineer, PKI & Cryptographic Systems

As a Senior Software Engineer on Cloudflare's PKI and cryptographic systems team, you will design and build the infrastructure that manages certificate lifecycles, protects private keys at scale, and advances Cloudflare's cryptographic stack into the post-quantum era. You work at the intersection of applied cryptography, distributed systems, and security engineering, on infrastructure that a large fraction of the Internet depends on. This is an early-stage role on a growing team, and the design decisions you make in the first year will shape how Cloudflare's certificate and key infrastructure operates for years to come.

What you'll do

• Design and build core PKI systems including certificate lifecycle management, X.509 issuance and validation logic, key parameter enforcement, and policy engines aligned with industry standards such as CA/Browser Forum guidance and browser root program policies
• Own the cryptographic core by integrating with FIPS 140-2 Level 3 and Level 4 HSMs via PKCS#11 and vendor-native SDKs, building key ceremony and key-lifecycle tooling, and enforcing strict key-usage boundaries in code
• Automate at scale by building and evolving ACME-based issuance and renewal pipelines, short-lived certificate rotation, and revocation mechanisms that serve at Cloudflare's global scale
• Instrument transparency and audit trails by integrating with Certificate Transparency, building append-only tamper-evident logging, and designing evidence pipelines that hold up to rigorous third-party audit
• Maintain accreditation and respond to a changing compliance landscape under CA/B Forum, WebTrust, and root store program frameworks, participating in public incident disclosure and regular third-party audits
• Represent Cloudflare in the WebPKI community by writing public CA incident reports and serving as a primary contact with the WebPKI community, with clear technical writing as a core responsibility
• Ship the post-quantum future by contributing to Cloudflare's ongoing post-quantum migration, including work on post-quantum encryption and authentication
• Own code end-to-end from design through production incident response, building the observability, runbooks, and on-call posture that keep the service inside SLO
• Partner across the organization with SSL/TLS product teams, HSM and data-centre infrastructure teams, the Cloudflare Research applied cryptography group, and adjacent product teams that consume PKI as a platform
• Mentor other engineers joining an early-stage team, run design reviews, and establish the engineering standards, threat models, and secure-development practices this team will operate under for years

What you bring

• 5+ years of production systems software experience with a strong operational track record, having carried a pager for something people depend on
• Deep working knowledge of applied cryptography and PKI, including X.509, ASN.1/DER, RFC 5280, CRL distribution, Certificate Transparency, ACME, and the CA/Browser Forum Baseline Requirements
• Familiarity with HSMs, including PKCS#11 integration, key ceremonies, key-attestation flows, and understanding of what FIPS 140-2/3 validation means in production
• Strong systems programming background in at least one of Go, Rust, or C/C++
• Distributed systems fluency, having built or operated globally replicated, availability-critical services with strict correctness guarantees
• Experience designing and operating database schemas for high-integrity systems such as Postgres or equivalent
• Security-hardened system design instincts including threat modelling, defence in depth, least privilege, and secure key handling
• Comfort with high-consequence work and the temperament to move quickly while maintaining the discipline to be careful

Nice to have

• Direct experience working on or with a publicly-trusted or private CA, or a large-scale internal PKI such as Let's Encrypt / Boulder, Google Trust Services, DigiCert, Sectigo, ISRG, Entrust, Microsoft PKI, HashiCorp Vault PKI, step-ca, or CFSSL
• Experience with crypto/x509 libraries such as BoringSSL, OpenSSL/AWS-LC, CFSSL, or an equivalent PKI codebase
• Experience with WebTrust for CAs, WebTrust BR, or WebTrust Network Security audit engagements
• Familiarity with post-quantum cryptography including ML-DSA, ML-KEM, hybrid signature schemes, and the current state of PQ signature standardisation
• Familiarity with emerging browser trust-establishment proposals such as Merkle Tree Certificates
• Prior participation in the CA/Browser Forum, IETF LAMPS / TLS / PLANTS / PQUIP working groups, the transparency.dev community, or a browser root program review
• Experience running or automating offline key ceremonies
• Experience operating Certificate Transparency log infrastructure or CT monitoring at scale
• Familiarity with formal methods, differential fuzzing, or property-based testing for cryptographic protocol code
• Kubernetes experience

What we offer

• Competitive salary of €66,000 - €83,000 annually for Portugal-based hires
• Eligibility to participate in Cloudflare's equity plan
• Comprehensive health and welfare benefits including medical, dental, and vision insurance, flexible spending accounts, fertility and family forming benefits, and on-demand mental health support
• Financial benefits including short and long term disability insurance, life and accident insurance, and 401(k) retirement savings plan
• Flexible paid time off covering vacation and sick leave, plus leave programs for parental, pregnancy health, medical, and bereavement leave
• Hybrid work available in Austin, London, or Lisbon

About Cloudflare

Cloudflare runs one of the world's largest networks that powers millions of websites and Internet properties for customers ranging from individual bloggers to SMBs to Fortune 500 companies. The company protects and accelerates Internet applications without adding hardware, installing software, or changing code. Cloudflare was named to Entrepreneur Magazine's Top Company Cultures list and ranked among the World's Most Innovative Companies by Fast Company.