Masked Card Number (PAN Masking) Regex for Go

What this pattern does

This page provides a well-structured, multi-part regular expression for matching masked card number (pan masking), ported and verified for Go. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. The snippet below is ready to drop into your Go project — whether you're validating in a Gin handler, a gRPC service, or a command-line tool.

Go Implementation

// Masked Card Number (PAN Masking)
// ReDoS-safe | RegexVault — Finance > Card Numbers

package validation

import "regexp"

var maskedCardNumberPanMaskingRe = regexp.MustCompile(`^[X*]{12}[0-9]{4}$|^[X*]{8}[0-9]{4}$|^[X*]{11}[0-9]{4}$`)

func ValidateMaskedCardNumberPanMasking(s string) bool {
    return maskedCardNumberPanMaskingRe.MatchString(s)
}

// Example
// fmt.Println(ValidateMaskedCardNumberPanMasking("XXXXXXXXXXXX1234")) // true

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Card Numbers category and carries a ReDoS-safe certification. That matters for Go developers because Go's RE2 engine is inherently safe from catastrophic backtracking, but this pattern has been additionally verified for correctness. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

PCI-DSS allows displaying first 6 and last 4 digits for debugging. This pattern shows only last 4. For display in UI, use: [\*X]{8,12}[0-9]{4} adjusted for 13/15/16-digit cards.