3 Ways to validate credit cards in PHP (with examples)

Overview

Credit card validation is an essential part of any online payment processing system. Validating a credit card before attempting a transaction can save time, reduce fraud, and improve the overall user experience. In this tutorial, we’ll explore several methods for validating credit cards in PHP, including the Luhn algorithm, regular expression matching, and utilizing third-party APIs. We will provide you with hands-on code examples to help you implement these validation techniques in your PHP applications.

Understanding Credit Card Validation

Before diving into the code examples, it’s important to understand what we mean by credit card validation. Validation refers to the process of ensuring that the credit card number provided is in a valid format and passes certain checks such as the Luhn check. However, validation does not mean that the card is legitimate or has sufficient funds; this is authorization, which requires a separate process typically involving communication with the card-issuing bank.

The Luhn Algorithm

The Luhn algorithm, also known as the modulus 10 or mod 10 algorithm, is a simple checksum formula used to validate a variety of identification numbers, including credit card numbers. Most card numbers adhere to this pattern, making it an ideal primary check for credit card validation.

A PHP function implementing the Luhn algorithm might look like this:

function luhn_check($number) {
  $number = preg_replace('/\D/', '', $number); // Remove any non-numeric characters
  $length = strlen($number);
  $sum = 0;
  $is_odd = $length % 2;

  for ($i=0; $i < $length; $i++) {
    $digit = $number[$i];
    if (($i % 2) === $is_odd) {
      $digit *= 2;
      if ($digit > 9) {
        $digit -= 9;
      }
    }
    $sum += $digit;
  }
  return ($sum % 10 === 0);
}

To use this function, you simply provide it with a credit card number as an argument, and it will return a boolean indicating whether the card number is potentially valid or not.

Regular Expression Matching

Another way to validate credit card numbers is to use regular expressions. Regular expressions can check whether a number conforms to the patterns typical of most credit card providers. The following is an example of a PHP function that uses regular expressions to validate credit card numbers.

First, define the regular expression patterns for major credit card companies:

$patterns = [
  'visa' => '/^4[0-9]{12}(?:[0-9]{3})?$/',
  'mastercard' => '/^5[1-5][0-9]{14}$/',
  'amex' => '/^3[47][0-9]{13}$/,'
  // Add additional card patterns here
];

Next, create a function that checks a credit card number against these patterns:

function regex_card_check($number, $patterns) {
  foreach ($patterns as $cardtype => $pattern) {
    if (preg_match($pattern, $number)) {
      return $cardtype;
    }
  }
  return false;
}

This function loops through the provided patterns and returns the card type if a match is found or false if no match is found.

Using Third-party APIs

For more comprehensive validation, you might consider using a third-party service. These services can not only perform the checks we’ve discussed but can also validate that the card is active, has funds available, and hasn’t been reported as lost/stolen. Many payment gateways offer API endpoints for this purpose.

While implementation details can vary, here’s a simplified example of how such a request might look in PHP when using a fictitious API:

function external_card_check($number, $expiry_month, $expiry_year, $cvv) {
  $curl = curl_init();

  curl_setopt_array($curl, [
    CURLOPT_URL => 'https://example-creditcard-api.com/validate',
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_POST => true,
    CURLOPT_POSTFIELDS => http_build_query([
      'number' => $number,
      'exp_month' => $expiry_month,
      'exp_year' => $expiry_year,
      'cvv' => $cvv,
    ]),
  ]);

  $response = curl_exec($curl);
  curl_close($curl);

  $result = json_decode($response);
  return $result->isValid;
}

Note that you’ll need to replace the URL and parameters with those provided by the actual API provider you choose. Be aware that this service usually isn’t free, and you’ll often need to handle additional security requirements, such as authentication tokens.

Conclusion

In this tutorial, we have explored various methods for validating credit card information using PHP code. Modulo checks with the Luhn algorithm, pattern matching with regular expressions, and integration with third-party APIs all serve as powerful tools for ensuring that credit card numbers are entered correctly. Remember, though, that validation is not the same as authorization or transaction completion, and it’s just the first step in a secure payment processing workflow.