Online transaction authorization

Transactions go online when an ARQC has been requested. The ARQC is sent in the authorisation message. The card generates the ARQC. Its format depends on the card application. EMV does not specify the contents of the ARQC. The ARQC created by the card application is a digital signature of the transaction details, which the card issuer can check in real time. This provides a strong cryptographic check that the card is genuine. The issuer responds to an authorisation request with a response code (accepting or declining the transaction), an authorisation response cryptogram (ARPC) and optionally an issuer script (a string of commands to be sent to the card).