The plaintiff's attorney submits a blockchain-anchored timestamp. The argument: inspection photos existed before the loss date, and the blockchain proves it. The defense moves to exclude. Not on relevance. On methodology. The expert can't adequately explain how the blockchain guarantees the hash wasn't manipulated before anchoring.
The judge schedules a Daubert hearing.
This is where blockchain evidence cases get decided. Not at trial. Pre-trial. A judge deciding whether the expert testifies at all. Get past Daubert with a solid foundation and the authentication case follows naturally. Fail it, and the timestamps are gone.
What Daubert Actually Requires
Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993) established the framework courts apply to expert testimony under Federal Rule of Evidence 702. The trial judge acts as gatekeeper. The expert's methodology must be scientifically valid and reliably applied to the facts at hand.
FRE 702 was amended in 2023 to make the reliability standard explicit. For expert testimony to be admissible, the opinion must reflect a reliable application of reliable principles to sufficient facts.
Courts applying Daubert typically evaluate: whether the theory has been tested, whether it's been peer-reviewed and published, the known error rate, whether there are controlling standards for the technique, and whether the methodology is generally accepted in the relevant field.
General acceptance is one factor, not a threshold. Blockchain anchoring doesn't need uniform judicial adoption to survive Daubert. The methodology has to be sound, documented, and demonstrable.
Why the Methodology Holds Up
SHA-256 is a published, deterministic hash function. Same input, same output, every time. Change one character in the file and the hash changes completely. This isn't proprietary. It's peer-reviewed, publicly specified, and used in TLS certificates, code signing, and financial system integrity checks. The error rate for false hash matches is effectively zero.
Polygon's consensus mechanism is documented. Bitcoin's proof-of-work has produced a verified public ledger for over 15 years. Transaction timestamps come from the network, not from any single party.
I'd argue this is the strongest part of the blockchain evidence case. The underlying cryptography isn't controversial. What gets challenged is the process connecting the file to the anchor, and that's where expert preparation matters.
When ProofLedger anchors a SHA-256 hash to both Polygon and Bitcoin, the expert's job at a Daubert hearing is to explain four things: the hash was computed from the specific file before anchoring; the blockchain transaction was recorded at a specific time, verifiable on public explorers; if the current file hash matches the anchored hash, the file hasn't been altered; and retroactively altering a Bitcoin transaction would require re-mining every subsequent block with majority network hash power. That last point is a computationally documented constraint, not a theoretical claim.
The FRE 901(b)(9) Connection
Authentication under FRE 901(b)(9) requires showing that evidence was produced by a process generating an accurate result. For blockchain timestamps, that foundation usually comes from expert testimony explaining the hashing and anchoring process.
Here's where the two analyses converge: the expert who lays the FRE 901(b)(9) foundation is the same expert who has to survive a Daubert challenge. If the court finds the methodology unreliable, the 901(b)(9) foundation fails with it. The procedural stages are separate. The underlying questions are identical.
FRE 902(13) offers an alternative path. Machine-generated records can self-authenticate through written certification, without live testimony. But if opposing counsel challenges the certification or the process behind the machine-generated record, the Daubert methodology questions come back anyway.
Brief the authentication argument and the Daubert argument together. They're defending the same methodology from two different procedural angles.
What the Expert Has to Be Ready to Say
Five things, clearly enough for a judge to evaluate reliability:
1. The hash function. SHA-256 is deterministic and collision-resistant. Security properties are peer-reviewed and publicly documented. False positive error rate is effectively zero.
2. The anchoring process. What happened between the file being hashed and the transaction being recorded. If there's a gap between hash computation and anchoring, the expert should know the order of events and be able to account for it.
3. The blockchain's timestamping mechanism. How Polygon and Bitcoin generate block timestamps, and what the consensus mechanism provides in terms of reliability. Bitcoin's block timestamps have a known network variance of up to two hours. That matters if the dispute turns on tight timing.
4. The independent verification path. How any third party can verify the anchor using the transaction hash, public block explorer, and merkle proof. ProofLedger's public verification endpoint (GET https://proofledger.io/api/v1/verify?hash=<sha256>) returns the proof record and explorer links without any account or authentication. That third-party verifiability is part of the Daubert methodology defense.
5. The scope of what's proved. A blockchain anchor proves a specific hash existed at a specific time. It doesn't prove who created the file, what the file depicts, or that the file predates the event in question. That last inference depends on the anchor timestamp predating the loss date. Knowing the limits of the proof, including what it doesn't prove, is part of surviving cross-examination.
Before the Hearing
Three things worth doing on any matter where blockchain-anchored evidence is in play.
Confirm the anchor timestamp predates the loss date and that this is independently verifiable on the public chain. Not from the vendor. From a block explorer that opposing counsel can check themselves.
Get the verification documentation before you need it. The public verification endpoint returns chain transaction data, explorer URLs, and the full proof record. Print it and include it in the exhibit file. If the expert needs to demonstrate independent verifiability at the hearing, this is the exhibit.
Brief the expert on dual-chain redundancy. ProofLedger anchors to both Polygon and Bitcoin. Two independent networks. A challenge to one chain's reliability doesn't defeat the other anchor. The expert should be prepared to explain why independent redundancy strengthens the process-reliability argument under FRE 901(b)(9).
Courts haven't uniformly ruled on blockchain evidence under Daubert. The methodology is defensible. Whether it gets defended well depends on the preparation that happens before the hearing.
Anchor before the loss, not after. Risk documentation, not claim documentation.
