Offline static data authentication (SDA) card authentication is a protocol for verifying that an EMV card is legitimate.
Offline card authentication is performed without an internet connection. EMV cards are pre-loaded with digitally-signed certificates and keys. Terminals have complementary keys provided by accepted payment brands at the time of terminal configuration.
In SDA, the terminal uses its public key to validate the card’s certificate. It then derives a key from the certificate and uses that key to validate the card’s static data.
SDA is the most widely available offline card authentication protocol, but it does not protect against fraud from skimmed and duplicated cards.
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