Digital Signatures, Non-Repudiation, and Proof of Delivery

Sometimes moving the file isn't enough — you need to prove things about it later. You need to prove who sent it, that nobody altered it, and that it truly arrived. Disputes over invoices, orders, and regulatory filings all come down to evidence. Evidence for file transfers is built from three materials: signatures, receipts, and trustworthy logs.

This series works through each. It explains digital signatures without the mathematics, and covers signing and verifying files in day-to-day practice. It covers what non-repudiation really means for a business argument and proof-of-delivery patterns for ordinary transfer channels. It explains why timestamps and clock discipline decide evidence quality, and how to assemble a coherent evidence pack when a transfer is disputed.

Articles in This Series

• Digital Signatures Explained with Files
  This article covers signing versus encrypting, and how a private key produces proof the public key can check. It explains exactly what a valid signature does and doesn't establish.
• Signing and Verifying Files in Practice
  Detached signatures walkthrough, verifying what partners send, key trust decisions, and wiring signing into routine workflows.
• Non-Repudiation: Proving Who Sent What
  The business problem behind the jargon — evidence elements, realistic strength in a dispute, and the gap between technical and legal proof.
• Proof-of-Delivery Patterns Outside AS2
  Receipts by design on plain channels: confirmation files, signed acknowledgments, and log correlation — and when structured receipts justify AS2.
• Timestamps, Clocks, and Evidence Quality
  Why unsynchronized clocks poison evidence, keeping transfer infrastructure on reliable time, and the trusted-timestamp concept in plain words.
• Building an Evidence Pack for a Disputed Transfer
  This article covers assembling logs, hashes, signatures, and receipts into a narrative that holds. It also covers the retention habits that make it possible months later.

Explore More Topics

This series is part of the Sysax file transfer topic library. The library covers the protocols, security practices, automation techniques, and operational skills behind reliable file transfer. The library pairs well with the practical tools we build. Sysax Multi Server is a secure FTP, FTPS, SFTP, and HTTPS server for Windows. Sysax FTP Automation schedules and scripts secure transfers so the routine ones run themselves.