The Card's UDK and the Application Transaction Counter (ATC) .
You cannot use a single master key for every card. You must derive a for each card using: arqc_gen.rar
To prevent "replay attacks," a new must be generated for every single transaction: The Card's UDK and the Application Transaction Counter (ATC)
The top-level secret stored in a Hardware Security Module (HSM). arqc_gen.rar
⚠️ Files with this name found on public forums or file-sharing sites are frequently flagged by security researchers as malware or phishing tools. They often contain "Remote Access Trojans" (RATs) or exploits targeting vulnerabilities in older versions of WinRAR.