mask all digits except first 6 and last 4 digits of a string( length varies )

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

This will work with any card number length:

var cardNumber = "3456123434561234";  var firstDigits = cardNumber.Substring(0, 6); var lastDigits = cardNumber.Substring(cardNumber.Length - 4, 4);  var requiredMask = new String('X', cardNumber.Length - firstDigits.Length - lastDigits.Length);  var maskedString = string.Concat(firstDigits, requiredMask, lastDigits); var maskedCardNumberWithSpaces = Regex.Replace(maskedString, ".{4}", "$0 "); 

Answer 2

Try this one. Simple and straight forward.

public static class StringExtensions {     public static string Masked(this string source, int start, int count)     {         return source.Masked('x', start, count);     }      public static string Masked(this string source, char maskValue, int start, int count)     {         var firstPart = source.Substring(0, start);         var lastPart = source.Substring(start + count);         var middlePart = new string(maskValue, count);          return firstPart + middlePart + lastPart;     } }