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

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

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 3

How about replacing a specific matched group using Regex :

        string cardNumber = "3456123434561234";
        var pattern = "^(.{6})(.+)(.{4})$";
        var maskedNumber = Regex.Replace(cardNumber, pattern, (match) =>
        {
           return Regex.Replace(String.Format("{0}{1}{2}",
           match.Groups[1].Value, // the first 6 digits
           new String('X', match.Groups[2].Value.Length), // X times the 'X' char
           match.Groups[3].Value) /*the last 4 digits*/,".{4}", "$0 "); //finally add a separator every 4 char
        });

Answer 4

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;
}

Answer 5

Possible implementation (acccepts varios formats e.g. numbers can be divided into groups etc.):

private static String MaskedNumber(String source) {
  StringBuilder sb = new StringBuilder(source);

  const int skipLeft = 6;
  const int skipRight = 4;

  int left = -1;

  for (int i = 0, c = 0; i < sb.Length; ++i) {
    if (Char.IsDigit(sb[i])) {
      c += 1;

      if (c > skipLeft) {
        left = i;

        break;
      }
    }
  }

  for (int i = sb.Length - 1, c = 0; i >= left; --i)
    if (Char.IsDigit(sb[i])) {
      c += 1;

      if (c > skipRight)
        sb[i] = 'X';
    }

  return sb.ToString();
}

// Tests 

  // 3456-12XX-XXXX-1234
  Console.Write(MaskedNumber("3456-1234-3456-1234"));
  // 3456123XXXXX1234
  Console.Write(MaskedNumber("3456123434561234"));

this implementation just masks the digits and preserve the format.

Answer 6

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;
    }
}