LUHN Algorithm – Validate credit card – in PHP
The Luhn algorithm or Luhn formula, also known as the “modulus 10″ or “mod 10″ algorithm, is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers and Canadian Social Insurance Numbers.
The formula verifies a number against its included check digit, which is usually appended to a partial account number to generate the full account number. This account number must pass the following test:
1. Counting from rightmost digit (which is the check digit) and moving left, Double the value of every alternate digit. For any digits that thus become 10 or more, take the two numbers and add them together. For example, 1111 becomes 2121, while 8763 becomes 7733 (from 2×6=12 → 1+2=3 and 2×8=16 → 1+6=7).
2. Add all these digits together. For example, if 1111 becomes 2121, then 2+1+2+1 is 6; and 8763 becomes 7733, so 7+7+3+3 is 20.
3. If the total ends in 0 (put another way, if the total modulus 10 is congruent to 0), then the number is valid according to the Luhn formula; else it is not valid. So, 1111 is not valid (as shown above, it comes out to 6), while 8763 is valid (as shown above, it comes out to 20).
/* Luhn algorithm number checker – (c) 2005-2008 shaman – www.planzero.org *
* This code has been released into the public domain, however please *
* give credit to the original author where possible. */
function luhn_check($number) {
// Strip any non-digits (useful for credit card numbers with spaces and hyphens)
$number=preg_replace(‘/\D/’, ”, $number);
// Set the string length and parity
$number_length=strlen($number);
$parity=$number_length % 2;
// Loop through each digit and do the maths
$total=0;
for ($i=0; $i<$number_length; $i++) {
$digit=$number[$i];
// Multiply alternate digits by two
if ($i % 2 == $parity) {
$digit*=2;
// If the sum is two digits, add them together (in effect)
if ($digit > 9) {
$digit-=9;
}
}
// Total up the digits
$total+=$digit;
}
// If the total mod 10 equals 0, the number is valid
return ($total % 10 == 0) ? TRUE : FALSE;
}
?>
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