A retail company must share a copy of its customer transaction database with an external analytics vendor. The dataset includes primary account numbers (PANs) subject to PCI DSS. The analytics team needs to correlate transactions by the same card across time but must never see, and the company must never transmit, the actual PAN values. The company also wants to keep a secure internal ability to reverse the process to the original PAN when a fraud investigation requires it. Which data protection technique best meets these requirements?