The tiny chip that gives every card payment a new code

How the reader wakes the chip

A chip card is usually passive: it has no battery. When you insert it, the payment terminal supplies a small electrical current through contacts on the card. The chip then uses its secret cryptographic key—a value stored inside the chip and designed not to be read out like ordinary card data—to help calculate a transaction-specific code.

The terminal provides details such as the amount and transaction data. The chip combines those inputs with its secret key and a changing counter to produce a cryptogram, a kind of digital proof for that purchase. The code changes as transactions change; it is not simply the card number sent again.

Why copying the stripe is different

A magnetic stripe stores data that a reader can copy and reproduce. That makes the stripe’s recorded information reusable: a counterfeit card can present the copied data as though it were the original.

Chip data is harder to reuse because a payment system can check whether the cryptogram is valid for the transaction being attempted. A code captured during one purchase should not authenticate a different purchase with a different amount or transaction data. The chip’s secret key stays on the card, so copying the visible card details does not provide what is needed to generate valid new codes.

A strong defense, not a complete shield

The cryptogram helps the card issuer or payment network assess whether a transaction is genuine, but it does not make every kind of fraud impossible. A stolen card can still be used in some circumstances, and online purchases generally do not involve the physical chip generating a code in the reader. Chip security is aimed especially at preventing counterfeit, in-person cards made from copied stripe data.

That is the key difference: a stripe offers a reusable record, while a chip can provide fresh evidence tied to the purchase in front of it.