Mask card numbers automatically to securely display and store sensitive financial info.
The Payment Card Industry Data Security Standard (PCI-DSS) is a set of strict security standards designed to ensure that all companies that accept, process, store or transmit credit card information maintain a secure environment.
A core rule of PCI-DSS is that the Primary Account Number (PAN) must be unreadable anywhere it is stored, including application logs, databases, and receipts.
When masking a PAN for display (like on a printed receipt or an online checkout page), PCI-DSS explicitly allows displaying the First 6 and the Last 4 digits of the card (e.g., 411122******1111).
The First 6 digits represent the Bank Identification Number (BIN) and the Last 4 digits are used by the customer to identify which card they used. The middle digits (the specific account number) must always be masked.
A common engineering failure occurs when developers log the entire HTTP request or API payload to a central logging system (like Datadog or Splunk) for debugging purposes.
If that payload contains an unmasked PAN, the entire logging cluster instantly falls under PCI compliance scope, which is a catastrophic compliance violation. Proper middleware must always redact or mask PANs before they are sent to logs.
Before masking or processing a card, systems often use the Luhn Algorithm (Modulus 10). It is a simple checksum formula used to validate a variety of identification numbers.
It detects accidental typos (like entering a 4 instead of a 5). It does not detect malicious attacks or verify that the card is actually authorized by the bank—it simply confirms the number is mathematically possible.
According to PCI-DSS, which digits of a Primary Account Number (PAN) are you generally allowed to display in plain text on a receipt?
