Application Transaction Counter (ATC)

What it is

The Application Transaction Counter (ATCApplication Transaction CounterA counter the card increments on every transaction, used to detect replay and cloning.View in glossary →) is a 2-byte counter the card increments on every GENERATE ACApplication CryptogramA cryptogram the card generates to approve or decline a transaction: TC (approve offline), ARQC (go online), or AAC (decline).. Because it is unique per transaction it is a key cryptogram input and a fraud signal: the issuer watches for gaps or repeats, which can reveal cloning or replay.

Where it appears

Returned by the card in the GENERATE ACApplication CryptogramA cryptogram the card generates to approve or decline a transaction: TC (approve offline), ARQC (go online), or AAC (decline). response; monitored by the issuer.

Specification reference

Defined in: EMV 4.x Book 3 (Application Specification), Annex A — Data Element Dictionary

Example values

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