Introduction

Updated: April 4, 2026 2 min read

What is Open TSA?

Open TSA is a free, open-source RFC 3161 Timestamp Authority operated in Europe. It allows anyone to add a cryptographically verifiable timestamp to any digital document — proving that the document existed in its exact form at a specific point in time.

Endpoint: https://tsr.open-tsa.eu — free, no account required, no rate limit for normal use.

What is RFC 3161?

RFC 3161 is an IETF standard (published 2001) for Time-Stamp Protocol (TSP). It defines how a Time Stamping Authority (TSA) can produce a digitally signed token that proves:

  • A specific document (identified by its hash) existed
  • At a specific point in time (certified by the TSA)
  • Without the TSA ever seeing the document itself

Why use timestamps?

Timestamps are used wherever the moment of existence of a document matters:

  • Document signing — prove a contract was signed before a certain date
  • Code signing — prove software was signed before a certificate expired
  • Audit trails — prove a log entry existed at a specific time
  • Intellectual property — prove a work existed before a claim
  • Legal compliance — GoBD, eIDAS, and other regulations require verifiable timestamps

How Open TSA differs

Most free TSA services are operated by a single private individual with no legal accountability, no redundancy, and no published source code. Commercial TSAs cost €200–1,000+/year.

Open TSA provides a third option: free like a community service, but with full source transparency, accountable operation, and a clear roadmap to public trust store inclusion.

Important: Open TSA uses its own root CA, which is not yet in public trust stores (Mozilla, Microsoft, Adobe). You must supply the CA certificates explicitly when verifying. See the Verification guide.