What is the name of this Checksum Algorithm?

Question

Does anyone know the formal / official name of the checksum algorithm used in the following functions?

---

function Checksum($number, $encode = true)
{
    if ($encode === true)
    {
        $result = 0;
        $number = str_split($number, 1);

        foreach ($number as $value)
        {
            $result = ($result + ord($value) - 48) * 10 % 97;
        }

        return implode('', $number) . sprintf('%02u', (98 - $result * 10 % 97) % 97);
    }

    else if ($number === Checksum(substr($number, 0, -2), true))
    {
        return substr($number, 0, -2);
    }

    return false;
}

---

function ifMB($entity, $reference, $amount = 0.00)
{
    $stack = 923;
    $weights = array(62, 45, 53, 15, 50, 5, 49, 34, 81, 76, 27, 90, 9, 30, 3);
    $argument = str_split(sprintf('%03u%04u%08u', $entity, $reference, round($amount * 100)), 1);

    foreach ($argument as $key => $value)
    {
        $stack += $value * $weights[$key];
    }

    return sprintf('%03u%04u%02u', $entity, $reference, 98 - ($stack % 97));
}

---

Thanks!

Answer 1

It's an error correcting code described in ISO7604, designed to detect various common kinds of mistakes people make when transcribing digit strings:

• Getting a single digit wrong
• Transposing two digits (e.g., 1324 instead of 1234)
• Adding or missing out a digit

The algorithm is mostly used in bank account number verification, but you can use it for pretty much any string of digits.

References:

• http://en.wikipedia.org/wiki/International_Bank_Account_Number#Calculating_and_validating_IBAN_checksums
• http://code.google.com/p/checkdigits/ (code implementing most of the standard ECCs)
• http://www.iso.org/iso/catalogue_detail.htm?csnumber=31531 (ISO standard page with some rationale)