Security & privacy
Tamper-evident QR labels
Tamper-evident QR labels make the sticker-overlay attack visible, destructible vinyl fragments on removal, void laminates leave a printed warning behind, and holographic overlays cannot be cleanly replaced. They cost pennies per label in volume, and they only work when paired with a routine physical audit of every deployed code.
The attack this defeats
The most practical QR attack requires no technology at all: print a malicious code on a sticker and paste it over a genuine one: the full anatomy is in stickers placed over real codes, and it is the engine behind parking scams and diverted payments. Tamper evidence attacks the attack: it cannot stop a sticker being applied, but it makes both the removal of your label and the presence of a foreign one visible.
Label materials compared
| Material | What happens on tampering | Typical use |
|---|---|---|
| Destructible ("eggshell") vinyl | Deliberately low tensile strength, fragments into small flakes rather than peeling off in one piece | Payment standees, meters, asset tags |
| VOID laminate | Peeling separates the layers, leaving a printed VOID or checkerboard pattern behind on the surface | Seals, service labels |
| Holographic overlay | The shimmer pattern cannot be photocopied or reprinted; a replacement is visibly different | Tickets, certification marks |
| Direct print on the surface | Nothing to peel: an attacker must cover rather than replace, and coverage is easier to spot | Menus, signage, packaging |
Direct printing deserves more credit than it gets: a code printed into the artwork of a sign has no label edges at all, so any label present is by definition foreign.
Design-level tamper evidence
The material is half the defence; the artwork is the other half:
- Print the destination domain in text under the code. A substituted sticker must now also fake the text, and any mismatch between printed domain and the scanner's preview banner is caught by the reader.
- Frame the code in your branding so a plain white overlay square is visually loud. Frames and labels are covered in frames and CTA labels.
- Print the payee name large on payment codes, so the name on the customer's confirmation screen can be checked against the sign.
- Keep the quiet zone inside the printed frame, so an overlay cannot hide behind "extra white space".
The audit routine
Tamper evidence is a sensor, not a shield. It only works if someone looks. A workable cadence:
| Surface | Check frequency |
|---|---|
| Public payment codes (standees, meters, chargers) | Weekly, and after any report |
| Customer-area codes (menus, tables, counters) | Monthly |
| Campaign materials (posters, flyers) | Once per campaign placement |
Each check takes seconds: run a finger over the code for edges, confirm the label is intact, then scan with a decoder and verify the destination matches the registry entry. Make it a named line on an existing checklist, audits that belong to nobody do not happen. The organisational wrapper is in the enterprise QR policy.
Cost reality
Tamper-evident stock is cheap insurance: destructible vinyl and void-laminate labels run to pennies per label at volume, a rounding error against the printed sign they protect: the audit time costs more than the labels do. Print your codes as a sticker sheet and the only change is the stock you order from the printer. For outdoor lifespan, combine with the materials advice in weatherproof QR stickers.
Limits
Be honest about what this does not solve. A determined attacker can replace an entire sign rather than overlay a label, and tamper evidence on the old sign is then irrelevant; a stolen genuine label re-sited elsewhere still scans. For codes whose authenticity truly matters, layer defences: signed payloads for cryptographic origin, tamper-evident stock for the physical layer, and the audit routine to close the loop.
FAQ
What is a tamper-evident QR label?
A label printed on stock designed to show interference: destructible vinyl that fragments on removal, laminates that leave a VOID pattern behind, or holographic overlays that cannot be cleanly replaced. The goal is making sticker-swap attacks visible.
Do tamper-proof stickers stop QR code scams?
They make the common overlay attack detectable rather than impossible. They work only alongside a routine where someone actually inspects and rescans the codes; unwatched tamper evidence catches nothing.
How often should printed QR codes be checked?
Weekly for public payment surfaces such as standees, meters and chargers; monthly for customer-area codes like menus; once per placement for campaign materials. Every check is a feel for edges plus a scan to confirm the destination.
What material is used for tamper-evident labels?
Most commonly destructible "eggshell" vinyl, which has deliberately low tensile strength so it flakes apart on removal, and VOID laminates that separate to leave a printed warning on the surface. Both cost pennies per label in volume.
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