Re: [PHP] Credit card number checker?

[Nathan Cook]

I ran across this function awhile back and it is what we use.
-------------------------------------------------------------------
function CCValidationSolution ($Number) {
    global $CardName;

    # 1) Get rid of spaces and non-numeric characters.
    $Number = OnlyNumericSolution($Number);

    # 2) Do the first four digits fit within proper ranges?
    #     If so, who's the card issuer and how long should the number be?
    $NumberLeft = substr($Number, 0, 4);
    $NumberLength = strlen($Number);

    if ($NumberLeft >= 4000 and $NumberLeft <= 4999) {
       $CardName = "Visa";
       if ($NumberLength > 14) {
           $ShouldLength = 16;
       } elseif ($NumberLength < 14) {
           $ShouldLength = 13;
       } else {
           return FALSE;
       }
    } elseif ($NumberLeft >= 5100 and $NumberLeft <= 5599) {
        $CardName = "MasterCard";
        $ShouldLength = 16;
    } else {
        return FALSE;
    }


    # 3) Is the number the right length?
    if ($NumberLength <> $ShouldLength) {
        $Missing = $NumberLength - $ShouldLength;
        if ($Missing < 0) {
        } else {
        }
        return FALSE;
    }


    # 4) Does the number pass the Mod 10 Algorithm Checksum?
    if (Mod10Solution($Number) == TRUE) {
        return TRUE;
    } else {
 return FALSE;
    }
}

function OnlyNumericSolution ($Number) {
   # Remove any non numeric characters.
   # Ensure number is no more than 19 characters long.
   return substr( ereg_replace( "[^0-9]", "", $Number) , 0, 19);
}

function Mod10Solution ($Number) {
    $NumberLength = strlen($Number);
    $Checksum = 0;

    # Add even digits in even length strings
    # or odd digits in odd length strings.
    for ($Location = 1 - ($NumberLength % 2); $Location < $NumberLength;
$Location += 2) {
        $Checksum += substr($Number, $Location, 1);
    }

    # Analyze odd digits in even length strings
    # or even digits in odd length strings.
    for ($Location = ($NumberLength % 2); $Location < $NumberLength; $Location
+= 2) {
        $Digit = substr($Number, $Location, 1) * 2;
        if ($Digit < 10) {
            $Checksum += $Digit;
        } else {
            $Checksum += $Digit - 9;
        }
    }

    # Is the checksum divisible by ten?
    return ($Checksum % 10 == 0);
}

// Usage
if (CCValidationSolution($Number) == TRUE) {
    echo "GOOD";
} else {
    echo "Bad card!";
}
-------------------------------------------------------------------

Good Luck!

Nathan Cook
[EMAIL PROTECTED]

----- Original Message -----
From: "Dr. Evil" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Monday, July 16, 2001 4:12 PM
Subject: [PHP] Credit card number checker?


>
> I know that credit cards have standard formats: There's a standard
> number of digits, and whether the card is Visa, MC, Amex, etc is
> encoded in the number, and there is some kind of checksum, and I think
> the expiration is also encoded in the number.  All of this is obvious
> stuff that anyone designing such a system would do.
>
> I'm wondering if anyone can refer me to a site that describes what
> this format is, so I can write some PHP code that will check to see if
> a credit card number format is correct.  I don't even want to try to
> run the card through my merchant account if the format is obviously
> wrong.  I assume that banks check the rejection rate on their merchant
> accounts, and too many bogus cards would not look good.
>
> I did a quick search on the web, and there are a vast number of
> "hacker" credit card number generators, but that isn't exactly what
> I'm looking for.
>
> Thanks
>
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