ABOUT JOIN.TECH

David has worked in payment and financial infrastructure environments at Worldline and PostFinance in Switzerland, with a focus on security-sensitive backend systems, cryptographic infrastructure and compliance-relevant engineering.

• Payment Systems: backend systems, APIs and transaction-related infrastructure.
• HSM Engineering: applied work with hardware security modules and payment-related cryptographic protocols.
• Payment Security: experience with PIN security, EMV-related topics, TR-31, TR-34, ISO 9564 and related standards.
• Compliance: PCI PIN, PCI DSS and PCI P2PE-related engineering and audit preparation.
• Migration Work: technical leadership and implementation support for large-scale payment security transitions.

join.tech supports organizations with architecture, system discovery, integration and transition work, particularly where systems are long-lived, operationally relevant or difficult to replace.

• System Discovery: inventory and analysis of systems, interfaces, dependencies and operational risks.
• Integration Architecture: APIs, EDI, messaging and data flows across organizational and technical boundaries.
• Migration Preparation: technical assessment and planning before major system changes.
• Technical Leadership: structured support for decisions, reviews, supplier coordination and architecture oversight.
• Documentation: decision records, system maps and technical summaries to reduce ambiguity and cognitive load.

Before focusing fully on software and security engineering, David worked in archaeology and cultural heritage contexts, including documentation, inventory and data management for research and public-sector environments.

• Cultural Heritage: work with archaeological documentation, inventories and records management.
• Research Contexts: practical experience in environments where data quality, documentation and long-term preservation matter.
• Data Management: databases, image archiving, GIS-related workflows and technical support for domain-specific processes.
• Bridging Domains: experience translating between specialist domain knowledge and practical technical implementation.

Independent projects are used to explore practical engineering topics, applied cryptography, developer tooling and systems analysis.

• Applied Cryptography: Rust and Python projects related to cryptographic primitives, test data and payment security.
• Developer Tools: command-line and workflow tools developed for practical daily engineering use.
• System Discovery: ongoing work on internal tooling for discovery, reconnaissance and technical inventory assessments.
• Open Source: selected personal and technical projects are available on GitHub.

• Description: Technical leadership and implementation work for the migration of payment card security standards across large card portfolios.
• Role: Project Lead, Lead Developer
• Focus: PIN security, HSM integration, backend APIs, migration planning and operational coordination.
• Environment: Regulated financial and payment infrastructure.

• Description: Development and integration work around hardware security modules, cryptographic key handling and payment security protocols.
• Focus: TR-31, TR-34, ISO 9564, EMV-related security topics, cryptographic test data and secure transaction flows.
• Technologies: C, Python, C#, SQL, HSM APIs and payment-specific interfaces.

• Description: Assessment and documentation of digital assets, system dependencies, interfaces and operational risks before migration or modernization.
• Focus: clarity before change, dependency mapping, interface discovery, technical risk identification and decision support.
• Outcome: improved understanding of the system landscape as a basis for architecture and transition decisions.

• Description: Work on integration-heavy environments involving operational systems, external partners and long-lived data exchange processes.
• Focus: APIs, EDI, messaging, data pipelines, interface documentation and maintainable operational handover.
• Environment: Logistics, payment systems and business-critical backend infrastructure.

• Description: Technical work in research and cultural heritage environments, including data management, documentation and domain-specific tooling.
• Focus: structured records, inventories, databases, image archiving and practical support for specialist workflows.
• Relevance: experience at the boundary between domain expertise and software engineering.

• Architecture: system design, architecture reviews, transition planning, technical decision support.
• Integration: APIs, EDI, messaging, data flows, backend interfaces and operational system boundaries.
• Security: security-conscious architecture, HSMs, cryptography, key management, PCI-relevant systems.
• Programming: Rust, Python, C/C++, C#, Java, Bash.
• Databases: PostgreSQL, SQL, data modelling, operational databases and migration support.
• Linux & Operations: Debian Linux, diagnostics, automation, service operation, observability and troubleshooting.
• Tools: Git, JIRA, Jenkins, Docker, LaTeX, Neovim, tmux, Wireshark, nmap and related engineering tools.

• Computer Science: Master of Science in Computer Science, University of Hagen.
• Applied Cryptography: academic work in traditional cryptography, post-quantum cryptography and electronic remote voting systems.
• Systems Engineering: academic and practical work involving C, compilers, algorithms and software engineering.
• Humanities & Research: earlier academic and practical background in Egyptology, archaeology and cultural heritage documentation.

• Company: LNL join.tech FlexCo
• Location: Vienna, Austria
• Primary Contact: David Schmid
• Role: Principal Technologist
• Email: mail@join.tech
• GitHub: 5n00py