using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        StringBuilder a = new StringBuilder();

a.AppendLine("line with no PII data.");

a.AppendLine("line with cvv: 123 data.");

a.AppendLine("line with cvc2: 123 data and some additional digits: 123.");

a.AppendLine("line with 23cvc2: 123 data with digits before and after.");

a.AppendLine("line with acvc: 123 data with the PII field surrounded by characters.");

a.AppendLine("line with cvca: 123 data with the PII field surrounded by characters.");

a.AppendLine("line with _cvc: 123 data with the PII field surrounded by special characters.");

a.AppendLine("line with -cvc: 123 data with the PII field surrounded by special characters.");

a.AppendLine("line with cvc_: 123 data with the PII field surrounded by special characters.");

a.AppendLine("line with cvc-: 123 data with the PII field surrounded by special characters.");

a.AppendLine("line with cvc-: 123 data with the PII field surrounded by special characters.");

a.AppendLine("line with __cvc: 123 data with the PII field surrounded by special characters.");

a.AppendLine("line with --cvc: 123 data with the PII field surrounded by special characters.");

a.AppendLine("line with cvc__: 123 data with the PII field surrounded by special characters.");

a.AppendLine("line with cvc--: 123 data with the PII field surrounded by special characters.");

a.AppendLine("line with cvc--: 123 data with the PII field surrounded by special characters.");

a.AppendLine("Some real life  data next");

a.AppendLine(@"         ""cardholder"": ""54**********0018"",");

a.AppendLine(@"         ""nvr_entr_id"": ""54**********0041"",");

a.AppendLine(@"         ""cvc_indnt_cd"": ""33"",");

a.AppendLine(@"         ""cvc_indnt_2_cd"": ""333"",");

a.AppendLine(@"         ""cvv_encd_cd"": ""333"",");

a.AppendLine(@"         ""entr_pi_id"": ""54**********0041"",");

a.AppendLine(@"         ""crd_exp_dt"": ""2706"",");

a.AppendLine(@"         ""crd_srvs_pin"": ""201""");

a.AppendLine(@"         <cardholder>54**********0018</cardholder>,");

a.AppendLine(@"         <nvr_entr_id>54**********0041</nvr_entr_id>,");

a.AppendLine(@"         <cvc_indnt_cd>33</cvc_indnt_cd>,");

a.AppendLine(@"         <cvc_indnt_2_cd>333</cvc_indnt_2_cd>,");

a.AppendLine(@"         <cvv_encd_cd>333</cvv_encd_cd>,");

a.AppendLine(@"         <entr_pi_id>54**********0041</entr_pi_id>,");

a.AppendLine(@"         <crd_exp_dt>2706</crd_exp_dt>,");

a.AppendLine(@"         <crd_srvs_pin> 201 </crd_srvs_pin>");

​

​

​

​

​

​

​

​

​

​

​

​

​

        string theText =  a.ToString();

        var lines = theText.Split(

        new string[] { Environment.NewLine },

        StringSplitOptions.None

        ).ToList();

        StringBuilder b = new StringBuilder();

        lines.ForEach(x => {

            if (Regex.IsMatch(x, @"(?<![^\W_\d])(cvv|cvc|expir|expr|exp|pin)(?![^\W_\d])"))

            {

                b.AppendLine(Regex.Replace(x, @"\d", "*"));

            }

            else

            {

                b.AppendLine(x);

            }

        });

        Console.WriteLine(b.ToString());

    }

}