There are six mainstream ways to prove that digital content existed at a point in time or that a process produced it: blockchain anchoring (OpenTimestamps), RFC 3161 timestamp authorities, hosted witness services (mpps.io), self-signed receipt SDKs, C2PA content credentials, and SLSA build provenance. They differ in trust model, latency, metadata support, and what question they actually answer. This page compares them honestly — including where mpps.io is the wrong choice.
| Approach | Trust model | Latency | Structured metadata | Cost | Best for |
|---|---|---|---|---|---|
| OpenTimestamps | Bitcoin proof-of-work — trustless once confirmed | Hours (block confirmation); instant partial proof | None — bare hash only | Free | Maximum-decentralization timestamping where hours of latency and no metadata are acceptable |
| RFC 3161 TSA (DigiCert, GlobalSign, freeTSA) |
Trust the timestamp authority's CA-managed key | Seconds | None — hash + timestamp token | Free–paid, often per-seal or subscription | Code signing and PKI toolchains that already speak RFC 3161 (ASN.1/DER tooling) |
| mpps.io | Trust an independent witness: AWS KMS HSM keys + S3 Object Lock Compliance storage; offline-verifiable | One HTTP round trip (<1s) | Yes — action name, artifact/input hashes, workflow context, parent-receipt chaining | Free (10/hr), no API key | AI agent and CI workflows that need structured, instantly-created, independently verifiable receipts |
| Self-signed receipt SDKs (e.g. Agent Receipts / Obsigna) |
The agent or its proxy signs with keys the operator holds | Instant, local | Yes — rich, per-tool-call | Free (self-hosted) | Internal observability and audit trails where the operator's word is accepted |
| C2PA | Signed manifests embedded in media, CA-issued creator credentials | At creation time | Yes — media provenance chain | Free spec; tooling varies | Images, video, and audio where provenance must travel inside the file |
| SLSA / in-toto | Build platform signs provenance attestations | At build time | Yes — build recipe, materials | Free | Software supply-chain provenance for packages and container images |
Who needs to believe the record, and do they trust you?
Honest limits, because they matter more than features:
Agent work is disputed at the level of actions: what task, which inputs, which outputs, in which workflow. Bare-hash timestamping loses that structure; self-signed receipts keep the structure but lose independence; media-embedded credentials don't fit reports, patches, and datasets. A detached, structured, independently signed receipt — action + artifact hashes + context, signed by keys the operator never touches, stored where nobody can rewrite it — is the combination the other tools don't cover. That is the gap mpps.io fills, and the receipt format is an open spec (MIT).