Long-Term Contract Records, Provable Years Later
On 15–20 year contracts, prove cryptographically that a record legitimately existed and was legitimately amended at the time — without revealing its contents — even when amounts, specs, or inspection records are disputed years later.
For long-term contract owners
Prove years later that surviving records weren't rewritten — ending the doubt over price, spec, and whether the inspection really happened.
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Long-term maintenance / contract managers in manufacturing and critical infrastructure (power, water, transport)
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Public-sector teams accountable for ledgers and inspection records
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Teams troubled by "we have records but can't prove they're untampered" in audits or disputes
Hand over the source, or just the facts?
Nothing changes on the floor. Everything changes for the receiver.
① Your team just saves, as always.
- The usual step
- Fill in the record and save
- On save
- A proof is attached (API, behind the scenes)
- The document itself
- never sent
② They just open a link.
- Proven fact
- was validly approved / amended at this point in time
- the ledger and original contracts
- not shown
- Login / keys
- not needed
- The document stays private — the record itself is never sent or disclosed.
- Independent verification — the receiver just opens a link. No account, no keys.
- Edits are detected — even a one-character edit fails verification.
We anchor the moment a contract, quote, or inspection record is created. The original stays in-house (or in your current system); what leaves is only the cryptographic fact of when, by whom, under which content hash, and tamper-free it existed. Even after amendments, "it legitimately existed and was legitimately amended" can be proven without revealing the contents.
However many years later a dispute or audit arrives, the parties, auditors, and third parties verify the same proof independently — without disclosing the original data.
Why the usual methods fall short.
Only work that needs all three at once — pass without exposing, independent verification, tamper-evidence — is Lemma's domain.
| Method | Pass without exposing | Independent verification | Tamper-evident | What happens |
|---|---|---|---|---|
| Access control / permissions | △ | ✗ | ✗ | “Someone inside could have edited it” remains possible |
| Masking / redacted copies | △ | ✗ | ✗ | Redaction work grows; the original is still unproven |
| Encrypt and store / send | ✓ | ✗ | ✗ | To verify, the receiver needs it disclosed after all |
| Lemma (ZK proof)the only one with all 3 | ✓ | ✓ | ✓ | The receiver just opens a link |
How it works — and how to start.
We help design disclosure scope and retention, run the PoC, and support production.
Start with a 30-minute call.
Using the Metawater work as a template, we'll confirm in the first 30 minutes where to start anchoring in your ledgers/contracts.
Find the case that matches your industry and problem
Browse all 36 use cases →TRY LEMMA
Run it yourself.
No sales call needed — start hands-on with Lemma's products.