mask all digits except first 6 and last 4 digits o

Question

I have a card number as a string, for example:

string  ClsCommon.str_CardNumbe r = "3456123434561234";

The length of this card number can vary from 16 to 19 digits, depending on the requirement.

My requirement is that I have to show the first six digits and the last 4 digits of a card number and mask the other characters in between with the character 'X'.

I have tried using subString and implemented it separately for 16,17,18,19 digits..

I split string(ClsCommon.str_CardNumber) to 5 strings (str_cardNum1, str_cardNum2, str_cardNum3, str_cardNum4, str_cardNum5 - 4 digits for each string..remaining digits for 5th string)

All the strings are placed in ClsCommon file. Based on that I implemented the below, which works perfectly:

if (ClsCommon.str_CardNumber.Length == 16) {
    txtmskcrdnum.Text = string.Concat(ClsCommon.str_cardNum1, " ", ClsCommon.str_cardNum2.Substring(0, 2), "XX", " ", "XXXX", " ", ClsCommon.str_cardNum4);

}
if (ClsCommon.str_CardNumber.Length == 17) {
    txtmskcrdnum.Text = string.Concat(ClsCommon.str_cardNum1, " ", ClsCommon.str_cardNum2.Substring(0, 2), "XX", " ", "XXXX", " ", "X", ClsCommon.str_cardNum4.Substring(1, 3), " ", ClsCommon.str_cardNum5);
}
if (ClsCommon.str_CardNumber.Length == 18) {
    txtmskcrdnum.Text = string.Concat(ClsCommon.str_cardNum1, " ", ClsCommon.str_cardNum2.Substring(0, 2), "XX", " ", "XXXX", " ", "XX", ClsCommon.str_cardNum4.Substring(2, 2), " ", ClsCommon.str_cardNum5);
}


if (ClsCommon.str_CardNumber.Length == 19) {
    txtmskcrdnum.Text = string.Concat(ClsCommon.str_cardNum1, " ", ClsCommon.str_cardNum2.Substring(0, 2), "XX", " ", "XXXX", " ", "XXX", ClsCommon.str_cardNum4.Substring(3, 1), " ", ClsCommon.str_cardNum5);
}
txtmskcrdnum.Text = ClsCommon.str_CardNumber.PadLeft(ClsCommon.str_CardNumber.Length, 'X').Substring(ClsCommon.str_CardNumber.Length - 4);

For multiple lengths, the above approach is not useful.

I want a single approach which displays the first 6 and last 4 digits and masks other digits with X. The final string should have a space between every 4 digits.

Answer 1

Linq saves coding lines, small code snippet.

Replaces with (*) char above 6 and bellow CardPan length minus 4

var CardPan = "1234567890123456";
var maskedPan = CardPan.Aggregate(string.Empty, (value, next) =>
{
    if (value.Length >= 6 && value.Length < CardPan.Length - 4)
    {
        next = '*';
    }
    return value + next;
});

Answer 2

One method:

string masked = null;
for (int i = 0; i < str_CardNumber.Length; i++) {
    masked += (i > 5 && i < str_CardNumber.Length - 4) ? 'X' : str_CardNumber[i];
    if ((i + 1) % 4 == 0)
        masked += " ";
}

Answer 3

I would do something like this (pseudo C# - take as rough idea to build upon).

Untested code ahead...

string MaskDigits(string input)
{
    //take first 6 characters
    string firstPart = input.Substring(0, 6);

    //take last 4 characters
    int len = input.Length;
    string lastPart = input.Substring(len - 4, 4);

    //take the middle part (XXXXXXXXX)
    int middlePartLenght = input.Substring(6, len - 4).Count();
    string middlePart = new String('X', 5);

    return firstPart + middlePart + lastPart;
}