OCR序列号校验位

Question

我想在OCR的帮助下读取大约16-20个字符（A-Z，0-9）的序列号。因为每次我想在序列号中添加一个校验字符时，所有字符都无法正确识别。 目前我找到了简单的Luhn mod N算法（Wikipedia)。这个算法对于换位错误不安全（09 => 90）。

Wikipedia的实施：

 char GenerateCheckCharacter(string input) {

    int factor = 2;
    int sum = 0;
    int n = NumberOfValidInputCharacters();

    // Starting from the right and working leftwards is easier since 
    // the initial "factor" will always be "2" 
    **//int index = 0;**
    for (int i = input.Length - 1; i >= 0; i--) {
        int codePoint = CodePointFromCharacter(input[i]);
        int addend = factor * codePoint;

        // Alternate the "factor" that each "codePoint" is multiplied by
        factor = (factor == 2) ? 1 : 2;
        **//factor = index;**


        // Sum the digits of the "addend" as expressed in base "n"
        addend = (addend / n) + (addend % n);
        sum += addend;
        **//index++;**
    }

    // Calculate the number that must be added to the "sum" 
    // to make it divisible by "n"
    int remainder = sum % n;
    int checkCodePoint = (n - remainder) % n;

    return CharacterFromCodePoint(checkCodePoint);
}

NumberOfValidInputCharacters（）将是36（A-Z，0-9）

但是如果我将“factor”变量修改为序列号内部字符的实际索引，那么它是否比以前更安全？ （参见代码中的** **行）