A timestamp service issues verifiable evidence that a particular piece of data existed at or before a specific point in time, without revealing the data’s contents. It accepts the hash of a document, binds it to a trusted time reference, and returns a signed timestamp token that anyone can later verify. Timestamp services support non-repudiation, intellectual-property priority, regulatory record-keeping, and long-term signature validation, and may be anchored in a trusted timestamp authority or in a public blockchain for trust-minimised proof of existence.
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- The purpose of a timestamp service is to answer a deceptively simple question with cryptographic rigour: did this exact data exist by this time? Proving priority of invention, the integrity of an audit log, or that a contract was signed before a deadline all reduce to verifiable proof of existence. A timestamp service provides this by binding a one-way hash of the data to an authoritative time, producing a token that is meaningful to anyone yet reveals nothing about the underlying content.
- In the classic trusted-authority model standardised by RFC 3161, a client hashes its document and sends only the hash to a Time-Stamping Authority. The authority appends its trusted time, signs the combination, and returns a token. Verification later re-hashes the document and checks the authority’s signature, confirming the data is unaltered and existed by the stated time. Trust rests on the authority’s signing key and the accuracy of its clock, typically traceable to a national time standard.
- Blockchain-anchored timestamping reduces reliance on a single trusted party. By committing a hash — often the root of a Merkle tree aggregating many documents — into a public blockchain transaction, a service inherits the chain’s immutability and public verifiability: the block’s timestamp and the inclusion proof together establish existence-by-time without trusting any individual authority. This approach trades the instant, signed assurance of an authority for trust-minimised, censorship-resistant evidence.
- Timestamp services are essential infrastructure for long-term trust. Digital signatures expire or are revoked when their keys age, but a timestamp proving a signature existed while its certificate was valid preserves that signature’s evidential value for decades — the basis of long-term archival signature formats used in legal and governmental records. Combined with hashing and signing, timestamping turns ephemeral cryptographic acts into durable, independently verifiable historical facts.