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Trusted timestamping authorities

Trusted timestamping authorities (TSAs) are services that sign a statement that a message imprint was received at a stated time. RFC 3161 is a common protocol for exchanging such tokens, but a TSA may also be part of a product-specific workflow.

What they do well

  • They provide a simple service boundary and a familiar evidence format for documents, signatures, and regulated workflows.
  • Commercial and organizational TSAs can offer support, certificate management, retention, and operational controls suited to their customers.
  • A single authority can be easier to integrate and govern than a federation.

Trust, privacy, and operational model

The usual trust model centers on one authority's signing key, certificate, clock, policies, and availability. The authority can receive only a message imprint, but request metadata and predictable hashes still require privacy review. The operator manages PKI, time sources, service availability, audit evidence, and token retention.

Difference from Witness

Witness distributes the signing decision across a configured threshold of independent witness nodes and supports local verification, Merkle proofs, and optional federation or external anchoring. A TSA generally provides one authority's signed time statement. Witness is not a replacement for a required TSA token or a certificate-based compliance process.

When to use one instead

Use a trusted TSA when an existing contractual, legal, or interoperability requirement calls for an authority-issued timestamp and a single-authority trust model is acceptable.