What is tag authentication, and which chips offer it?
A mechanism by which the chip demonstrates it holds a particular key, without that key ever crossing the air. The families differ in whether the proof changes on every read, whether a verifier must hold a matching secret, and how much infrastructure the checking side needs.
The shape of the exchange
The chip is manufactured holding a key. The key is not readable by any command, which is a property of the silicon rather than a setting.
A reader presents something, the chip computes a response using the key, and the response is checked by whoever holds the corresponding secret.
Nothing that crosses the air lets an observer produce a future response, which is exactly the property a readable value can never have.
Two families, roughly
One where a challenge is sent and the chip answers it. Each challenge is different, so each answer is different, and there is nothing to accumulate.
One where the chip produces a value that changes by itself on every read, without needing to be asked a question. Simpler for the reader, and it needs the verifier to keep track of what it has already seen.
The specific families, their commercial names and their per unit cost belong to the chip manufacturers' datasheets, which are maintained by them and change with product generations.
What does not change is the shape, and the shape is what a decision should be made on.
The verifier decides the cost
A chip that proves itself is useless without something able to judge the proof, and that something holds a secret.
That means a service you run, or one a supplier runs for you, reachable at the moment somebody taps. It means key management, and it means the arrangement has to keep working for as long as the tags are in the field.
The chips are quoted per thousand and look affordable. The service is quoted per year and is where the budget goes.
Any evaluation that prices the chip without pricing the verifier has priced the smaller half.
What to establish before buying
Who verifies, and what happens when that party stops. A scheme whose verifier disappears leaves tags that assert nothing.
Whether an ordinary phone can take part without a dedicated application, because for consumer facing schemes that decides adoption.
What happens to a tag that fails verification, since a scheme with no defined response to a failure will simply be ignored when it fires.
And whether the tag being genuine is actually the question, or whether the real question is about the item it is attached to.
Frequently asked questions
Does authentication stop copying?
It makes a copy useless rather than impossible. The copy cannot produce the proof, so it fails the check.
Can any phone verify an authenticating tag?
The phone relays the exchange. The judgement happens wherever the matching secret is held, which is normally a service.
What does it cost?
More per chip, and considerably more for the verification service and key management that have to run for the life of the deployment.
Which chips offer it?
Several families do, under names that change with product generations. The manufacturers' datasheets are the authority on that.