Simple PHP script to generate syntactically valid credit card numbers using the Luhn check. Also see http://en.wikipedia.org/wiki/Luhn_algorithm Not valid for making transactions anywhere!

luhn.php

<?

	$bin = $_POST['bin'];
	$length = $_POST['length'];
	if ( $length == 0 )
		$length = 16;

	if ( $bin != '' )
		$cardNumber = completed_number( $bin, $length );

	echo "Generate card number<br>";
	echo "<form action='index.php' method='post'>";

	echo "<table>";
	echo "<tr><td>BIN:</td><td> <input name='bin' value='$bin' onfocus='select()'/></td></tr>";
	echo "<tr><td>Length:</td><td> <input name='length' value='$length'/></td></tr>";
	echo "<tr><td>Card Number:</td><td> <input name='cardNumber' value='$cardNumber'/></td></tr>";

	echo "<input type='submit'>";
	echo "</form>";

	echo "<br>BINs: MC:51/16 to 55/16; VISA:4/13 and 4/16; AMEX: 34/15 and 37/15; VIAS: 9528/16";

/*
'prefix' is the start of the CC number as a string, any number of digits.
'length' is the length of the CC number to generate. Typically 13 or 16
*/
function completed_number($prefix, $length) {

    $ccnumber = $prefix;

    # generate digits

    while ( strlen($ccnumber) < ($length - 1) ) {
        $ccnumber .= rand(0,9);
    }

    # Calculate sum

    $sum = 0;
    $pos = 0;

    $reversedCCnumber = strrev( $ccnumber );

    while ( $pos < $length - 1 ) {

        $odd = $reversedCCnumber[ $pos ] * 2;
        if ( $odd > 9 ) {
            $odd -= 9;
        }

        $sum += $odd;

        if ( $pos != ($length - 2) ) {

            $sum += $reversedCCnumber[ $pos +1 ];
        }
        $pos += 2;
    }

    # Calculate check digit

    $checkdigit = (( floor($sum/10) + 1) * 10 - $sum) % 10;
    $ccnumber .= $checkdigit;

    return $ccnumber;
}

function credit_card_number($prefixList, $length, $howMany) {

    for ($i = 0; $i < $howMany; $i++) {

        $ccnumber = $prefixList[ array_rand($prefixList) ];
        $result[] = completed_number($ccnumber, $length);
    }

    return $result;
}

?>
john@dev:~/www/luhn$ cat index.php 
<?

	$bin = $_POST['bin'];
	$length = $_POST['length'];
	if ( $length == 0 )
		$length = 16;

	if ( $bin != '' )
		$cardNumber = completed_number( $bin, $length );

	echo "Generate card number<br>";
	echo "<form action='index.php' method='post'>";

	echo "<table>";
	echo "<tr><td>BIN:</td><td> <input name='bin' value='$bin' onfocus='select()'/></td></tr>";
	echo "<tr><td>Length:</td><td> <input name='length' value='$length'/></td></tr>";
	echo "<tr><td>Card Number:</td><td> <input name='cardNumber' value='$cardNumber'/></td></tr>";

	echo "<input type='submit'>";
	echo "</form>";

	echo "<br>BINs: MC:51/16 to 55/16; VISA:4/13 and 4/16; AMEX: 34/15 and 37/15; VIAS: 9528/16";

/*
'prefix' is the start of the CC number as a string, any number of digits.
'length' is the length of the CC number to generate. Typically 13 or 16
*/
function completed_number($prefix, $length) {

    $ccnumber = $prefix;

    # generate digits

    while ( strlen($ccnumber) < ($length - 1) ) {
        $ccnumber .= rand(0,9);
    }

    # Calculate sum

    $sum = 0;
    $pos = 0;

    $reversedCCnumber = strrev( $ccnumber );

    while ( $pos < $length - 1 ) {

        $odd = $reversedCCnumber[ $pos ] * 2;
        if ( $odd > 9 ) {
            $odd -= 9;
        }

        $sum += $odd;

        if ( $pos != ($length - 2) ) {

            $sum += $reversedCCnumber[ $pos +1 ];
        }
        $pos += 2;
    }

    # Calculate check digit

    $checkdigit = (( floor($sum/10) + 1) * 10 - $sum) % 10;
    $ccnumber .= $checkdigit;

    return $ccnumber;
}

function credit_card_number($prefixList, $length, $howMany) {

    for ($i = 0; $i < $howMany; $i++) {

        $ccnumber = $prefixList[ array_rand($prefixList) ];
        $result[] = completed_number($ccnumber, $length);
    }

    return $result;
}

?>