Digital Signatures, Non-Repudiation, and Proof of Delivery

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

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

Articles in This Series

• Digital Signatures Explained with Files
  Signing versus encrypting, how a private key produces proof the public key can check, and 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
  Assembling logs, hashes, signatures, and receipts into a narrative that holds — and the retention habits that make it possible months later.

Explore More Topics

This series is part of the Sysax file transfer topic library, which 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, a secure FTP, FTPS, SFTP, and HTTPS server for Windows, and Sysax FTP Automation, which schedules and scripts secure transfers so the routine ones run themselves.