See a buyer spot a fake ad offer.
Publishers can sign the ad space they sell. In this sample, a reseller copies that signature onto an offer the publisher never made. Pick the buyer's rule and see which offers stay in.
1. Signed
The publisher signs its ad offer. The signature covers the exact terms.
2. Copied
A reseller copies that signature onto an offer with new terms.
3. Checked
The buyer sees the terms no longer match what the publisher signed.
One rule decides which offers stay in.
Five sample offers, one buyer. The strictest rule is on. Tap another rule to compare.
The rule: buy only offers the publisher signed.
Both signed offers stay in, and the buyer picks one. The fake and the unproven offers are left out, each with a reason a person can read.
| Offer | Proof | Result | Why |
|---|---|---|---|
Northfield Sports Daily Sports ad space, signed with a compatible key. | Proof:Checks out | Stays inPicked | The publisher signed these exact terms. |
The Meridian Ledger Ad space backed by an article the publisher signed when it was published. | Proof:Checks out | Stays in | The publisher signed these exact terms. |
Harbor Weather Report Ad space whose listing proof has a signature that fails the check. | Proof:Fails | Left out | The signature fails the check. |
Culture Notes Weekly Ad space offered with no listing proof. | Proof:Fails | Left out | No signature came with this offer. |
Syndicated Reseller Offer An offer that reuses a valid listing signature for other terms. | Proof:Fails | Left out | Valid signature, substituted terms. These are not the terms the publisher signed. |
For the publisher: offers you signed stay in front of buyers who check. An offer that borrows your name is left out.
Try it on your own ad space.
Sign your own offers, so buyers can check their provenanceContent provenance: The record of where a piece of content came from and how it changed, carried with the content itself..
Test one property, ten URLs and one buyer rule. Your team reads the results in a table like the one above, with every proof attached.
More demos: try it yourself, no accountfor AI teamsfor publishersAI chatbot with signed answersprivate team walkthrough
For engineers
Show the technical detailThe signed offer terms, why the copied signature fails, the receipt, and checks that run in this browser.
The sample story
A made-up publisher, The Meridian Ledger, signs an article when it publishes, and the article backs the ad-space offer. The demo takes that article signature as given and does not check it. The checks below cover the offer.
The Meridian Ledger
Harbor District Approves the Port Expansion
- Content ID
meridian-ledger/port-expansion-2026-07- Property
article_inventory- Signing key
listing-2026-07- Article status
- Signed at publication. Sample context, not checked here.
The signed offer terms
The publisher signs a digest of the six offer terms below. Change any one, and the terms no longer match the signature.
currencyUSDprice10pricing_modelcpmpricing_option_idpo-verified-encypherproduct_idverified-encypherproperty_idarticle_inventory
Why the copied signature fails
The copied signature is cryptographically valid. What fails is the match. The signed digest covers the terms the publisher approved, and the new terms give a different digest. A signature cannot stop copying. The digest makes the swap detectable by any buyer who checks.
The signed receipt
Each run ends with a receipt you can keep and forward.
- Article: signed at publication in the sample story. The demo does not check it.
- Listing proof: the publisher signature covers the offer terms.
- Policy decision: each offer shows its result and a reason under the buyer rule.
- Run receipt: the run record is signed with the sandbox run key.
Receipt fields, with sample values.
sandbox_run_key1f6a2c3e-8d4b-4f0a-9c2d-5e7b1a3c9d40signature_verifiedtrueproof_scopeschema_digest_and_run_key_signaturerecord_key_thumbprintuM9xpCqvv29Z6IC-gh17R_AmwM_3YFOFdH6Po0a9760
Create. Mark. Endure.
Bring signed offers to your auctions. Tell us which side of the trade you work on.