The transaction key scheme is a technique in which data-encrypting keys change with each transaction in a manner that cannot be followed by a third party. This is typically of use in Electronic Fund Transfer at Point Of Sale (EFTPOS) systems where fund transfer requests and responses are exchanged between a retailer (EFTPOS terminal) and an acquirer, and then, optionally, between the acquirer and the card issuer.
The HSM supports as standard three techniques "The Racal Transaction Key Scheme (RTKS)", "Australian Transaction Key Scheme (AS2805)" and "Derived Unique Key Per Transaction (DUKPT)". There are command conflicts between the Racal and Australian schemes so only one can be selected in the security settings; see CS (Configure Security) console command.