Digital contract management platforms digitize workflows but lack end-to-end cryptographic security and strong privacy protection, leaving sensitive contract data vulnerable to unauthorized access. To address these limitations, this work presents daft, the first open-source web implementation of cyber-physical contracts, developed using the MERN stack (MongoDB, Express.js, React.js, Node.js). daft integrates TweetNaCl-based key-pair generation for digital signatures, end-to-end encryption for contract data, role-based access control for clients, freelancers, and administrators, sequential task validation to enforce milestone ordering, and SHA-256 hashing for tamper-proof audit logging. The platform supports the complete contract lifecycle including creation, cryptographic signing, milestone verification, payment processing, dispute resolution, and secure archiving. Evaluation demonstrates 100% signature verification accuracy, GDPR-compliant privacy preservation through a zero-trust architecture, and fully browser-based operation without external dependencies. The open-source release includes a JavaScript core library, reusable React modules, and a public demonstration platform, significantly lowering the technical barrier for adoption and establishing a verifiable foundation for privacy-preserving digital agreements.

Index Terms — Cyber-Physical Contracts, Privacy Preservation, Cryptographic Security, Digital Signatures, Sequential Task Validation, MERN Stack, GDPR Compliance.