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 automates issuance and renewal across a global network that handles tens of millions of certificate operations daily. 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 where 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 including 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 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, adapt to policy changes, participate in public incident disclosure and discourse, and participate in 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 through clear technical writing
• 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, Cloudflare Research applied cryptography group, and adjacent product teams that consume PKI as a platform
• Raise the bar by mentoring other engineers joining an early-stage team, running design reviews, and establishing the engineering standards, threat models, and secure-development practices this team will operate under

What you bring

• 5+ years of production systems software experience with a strong operational track record, including carrying 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
• Security-hardened system design instincts including threat modelling, defence in depth, least privilege, and secure key handling
• Temperament and discipline for high-consequence work where certificate mis-issuance or mis-revocation is a public, industry-visible event

Nice to have

• Direct experience working on or with a publicly-trusted or private CA, or 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, BoringSSL, OpenSSL/AWS-LC, CFSSL, or 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

• Estimated annual salary of €66,000-€83,000 for Portugal-based hires
• Equity participation in Cloudflare's equity plan
• Medical, dental, and vision insurance
• Flexible spending accounts for healthcare and commuting
• Fertility and family forming benefits
• On-demand mental health support and Employee Assistance Program
• Global travel medical insurance
• Short and long term disability insurance
• Life and accident insurance
• 401(k) retirement savings plan and Employee Stock Participation Plan
• Flexible paid time off covering vacation and sick leave
• Leave programs including parental, pregnancy health, medical, and bereavement leave
• Hybrid work 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 any Internet application online without adding hardware, installing software, or changing a line of code. Cloudflare was named to Entrepreneur Magazine's Top Company Cultures list and ranked among the World's Most Innovative Companies by Fast Company.