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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteAn RFC 3161 timestamp can provide evidence that a particular digest existed by the time stated in a TSA-signed token. It does not, by itself, stop a log operator from changing the log or showing different histories to different people. To make a hash-chain history auditable, preserve timestamped checkpoints and pair them with signed log roots, inclusion and consistency proofs, and independent monitoring.
What is an RFC 3161 timestamp?
RFC 3161 defines a way to ask a Time-Stamping Authority (TSA) to sign evidence about a digest and a time. In the standard hash-only workflow, the requester keeps the file, calculates its digest, and sends the TSA a message imprint: the digest together with the identifier for the hash algorithm used. The file itself need not be sent.
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The request, called a TimeStampReq, may also include a requested policy and a nonce. The TSA returns a TimeStampResp, which normally contains a signed TimeStampToken. That token binds the message imprint to the TSA’s asserted time and includes identifying and policy information. RFC 3161, published by the RFC Editor in August 2001 and updated by RFC 5816, requires a TSA to use a trustworthy source of time.
When the imprint recomputed from retained bytes matches the token’s imprint, the token links those bytes to the timestamp. The signature and certificate checks help establish that the token was issued by the identified TSA. As RFC 3161 puts it, a timestamping service supports assertions that a datum existed before a particular time; the strength of that assertion depends on trusting the TSA, its time source, and the validation evidence.
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Does timestamping a hash prove when a file was created?
No. It is evidence that the data represented by the digest existed no later than the TSA’s stated time, subject to the TSA’s trust assumptions. It does not establish the file’s exact creation time, its author, the truth of its contents, or whether it remained unchanged afterward. A file may have existed well before it was timestamped.
A self-asserted signing time is not an equivalent substitute. NIST SP 800-102, by Elaine B. Barker, explains that a signed message’s purported signing time does not assure when the private key was used unless the time’s accuracy can be trusted. A TSA token offers an external time assertion, but it is not stronger than the TSA and time source behind it.
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How do I verify an RFC 3161 timestamp?
Verification means checking both that the token refers to the exact data you retained and that the token’s signature and time evidence meet your trust requirements. A valid signature alone does not establish trustworthy time, and a correct digest match alone does not establish who issued the token.
- Keep the original bytes. Recompute the digest from the exact file or canonical checkpoint bytes. If you only have the original request, compare the request’s message imprint with the token. A change in bytes, encoding, or canonicalization can produce a different digest.
- Check the response and imprint. Confirm the TSA response status is acceptable, the token contains the expected imprint, and the hash algorithm identifier is the one expected. RFC 3161 specifies checking the token’s TSA certificate identifier as well.
- Validate the signature and certificate. Verify the token signature against the TSA certificate and validate its certificate chain, timestamping extended key usage, applicable policy, and certificate status. Retained revocation evidence, such as a CRL where applicable, can be important for later validation.
- Assess the time assertion. Check the TSA’s stated time against a trusted local time reference where one is available. A request nonce can help detect replay of an old response to a fresh request; it cannot independently prove clock accuracy when the client has no trusted clock.
- Preserve the validation record. Retain the request, response or token, TSA certificate chain, relevant status evidence, policy information, and the exact data that was hashed. These materials support later revalidation.
RFC 3161 warns that TSA signing keys have finite lifetimes. A token does not automatically remain easy to validate indefinitely: certificate expiry, loss of revocation evidence, policy changes, and weakening algorithms can complicate future checks. Long-term validation therefore requires an operational plan for preserving or renewing evidence, not just saving the token.
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OpenSSL documents a demonstration workflow using openssl ts -query to create a request, the separate tsget utility to transport a DER-encoded request to a timestamp server, and openssl ts -verify to verify a response with trusted CA material. The documentation also describes verification against a data file or request. Syntax varies by OpenSSL release, and the ts command does not itself send the request over HTTP. Using OpenSSL successfully does not, on its own, establish that a TSA is appropriate for production.
How do you prove a hash chain has not been rewritten?
A hash chain makes changes detectable only relative to a state that someone else has preserved or can verify. If an operator controls every copy and no checkpoint exists outside its control, it may be able to alter old entries and recompute every later hash. Calling such a chain “immutable” overstates what the hashes alone guarantee.
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For an append-only log, a stronger pattern is a Merkle transparency log. The log signs a tree root together with the tree size. An inclusion proof lets a user check that an entry belongs to that particular tree. A consistency proof lets a user check that a later tree extends an earlier one rather than replacing it. RFC 6962 describes Certificate Transparency as a model for publicly auditable, append-only logs; RFC 9162 specifies inclusion and consistency proof operations for CT version 2. These are useful examples, not a requirement that every system implement Certificate Transparency.
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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteProofs from the log are not enough if the operator can give different roots to different users. Independent monitors, witnesses, or gossip mechanisms can compare observed checkpoints and expose conflicting views. The key distinction is that a timestamp anchors a point in time, while log proofs and independent observation help establish how later states relate to that point.
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How should you anchor an append-only history?
Use a timestamp to anchor a precisely defined checkpoint, not an informal description of the log. The serialization of the checkpoint and what it commits to are design choices; RFC 3161 does not prescribe them.
- Define entries and bytes. Specify what one log entry represents and its canonical byte representation so independent parties hash the same data.
- Build the append-only structure. Add each entry to the chosen cryptographic structure. For a Merkle log, calculate the new root and record the corresponding tree size.
- Create and distribute a checkpoint. Serialize a deterministic checkpoint of the state. Publish or distribute a signed checkpoint or root, then calculate the digest of the checkpoint bytes and request an RFC 3161 timestamp for that digest.
- Return entry proofs. Provide users with inclusion proofs for their entries, and make consistency proofs available between tree sizes as the log grows.
- Compare independent observations. Have monitors fetch checkpoints and compare them. Witnesses or gossip can help reveal cases where different users receive inconsistent views.
- Verify each layer separately. Validate the timestamp token and its certificate and time assumptions separately from the log’s signature, inclusion proof, consistency proof, and monitoring evidence.
Preserve the checkpoint bytes, their digest, the timestamp request and response, and the validation material. If the checkpoint commits to a Merkle root, retain its tree size and the relevant proofs. A timestamp on the checkpoint digest can make a later replacement or backdating detectable when compared with the retained checkpoint and token. It cannot compel the operator to show every client the same history.
What each mechanism establishes
| Mechanism | What it helps establish | What it does not establish by itself |
|---|---|---|
| RFC 3161 timestamp token | A TSA signed an imprint and asserted a time for it. | Exact file creation time, authorship, truth, or a consistent history for all log users. |
| Hash chain or Merkle root | A commitment to a particular sequence or tree state; a change can be detectable when compared with a preserved prior state. | Protection against an operator recomputing history when no trusted checkpoint or outside observer has preserved the earlier state. |
| Inclusion proof | An entry belongs to a specified tree state. | That the specified tree is the only state shown to users, or that it extends an earlier state. |
| Consistency proof | A later tree extends an earlier tree under the log’s append-only rules. | That all users were shown the same roots; independent comparison is still needed to expose split views. |
| Independent monitors, witnesses, or gossip | Comparison of checkpoints can reveal inconsistent views of the log. | Trustworthiness of the TSA’s clock or validity of a timestamp token; those require separate checks. |
What should you retain, and what should you avoid sending?
- Keep the exact original file or canonical checkpoint bytes, plus the digest and algorithm identifier.
- Retain the timestamp request and response or token, TSA certificate chain, relevant revocation evidence, and TSA policy information.
- For a log checkpoint, preserve the signed root or checkpoint, tree size, inclusion and consistency proofs, and records of independently observed checkpoints.
- Do not send sensitive original content to the TSA when a digest is sufficient. A message imprint is a digest, but repeated identical digests can reveal that different users timestamped the same data, and low-entropy content may sometimes be guessed by hashing candidate values. Follow the organization’s data-handling and privacy policy.
The practical claim to make is narrow: the retained digest is supported by evidence that it existed by the TSA’s stated time, assuming the TSA and its time source are trusted. The claim that a file’s exact creation time is proven, or that history is impossible to rewrite, goes beyond what timestamping alone establishes.
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