Creating Fake Credit Card Numbers in c#

I recently had to create a credit card number generator, nothing nefarious, just we needed unique valid credit card numbers after asking on StackOverflow and getting a less than stellar response (for the first time). I came across something on DarkCoding.Net which did exactly what I wanted but was in Java, I’ve ported it over to c# and I hope you find it useful

Update

I recently rewrote this code. removing a couple of bugs and making it a bit more c# and bit less Java

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;

namespace CreditCardNumberGenerator
{
	public class RandomCreditCardNumberGenerator
	{
		/*This is a port of the port of of the Javascript credit card number generator now in C#
		* by Kev Hunter http://kevhunter.wordpress.com
		* See the license below. Obviously, this is not a Javascript credit card number
		 generator. However, The following class is a port of a Javascript credit card
		 number generator.
		 @author robweber
		 Javascript credit card number generator Copyright (C) 2006 Graham King
		 graham@darkcoding.net
		 This program is free software; you can redistribute it and/or modify it
		 under the terms of the GNU General Public License as published by the
		 Free Software Foundation; either version 2 of the License, or (at your
		 option) any later version.
		 This program is distributed in the hope that it will be useful, but
		 WITHOUT ANY WARRANTY; without even the implied warranty of
		 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
		 Public License for more details.

		 You should have received a copy of the GNU General Public License along
		 with this program; if not, write to the Free Software Foundation, Inc.,
		 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
		 www.darkcoding.net
		*/


		public static string[] AMEX_PREFIX_LIST = new[] {"34", "37"};


		public static string[] DINERS_PREFIX_LIST = new[]
		                                            	{
		                                            		"300",
		                                            		"301", "302", "303", "36", "38"
		                                            	};


		public static string[] DISCOVER_PREFIX_LIST = new[] {"6011"};


		public static string[] ENROUTE_PREFIX_LIST = new[]
		                                             	{
		                                             		"2014",
		                                             		"2149"
		                                             	};


		public static string[] JCB_15_PREFIX_LIST = new[]
		                                            	{
		                                            		"2100",
		                                            		"1800"
		                                            	};


		public static string[] JCB_16_PREFIX_LIST = new[]
		                                            	{
		                                            		"3088",
		                                            		"3096", "3112", "3158", "3337", "3528"
		                                            	};


		public static string[] MASTERCARD_PREFIX_LIST = new[]
		                                                	{
		                                                		"51",
		                                                		"52", "53", "54", "55"
		                                                	};


		public static string[] VISA_PREFIX_LIST = new[]
		                                          	{
		                                          		"4539",
		                                          		"4556", "4916", "4532", "4929", "40240071", "4485", "4716", "4"
		                                          	};


		public static string[] VOYAGER_PREFIX_LIST = new[] {"8699"};

		/*
      'prefix' is the start of the 	CC number as a string, any number
		private of digits	'length' is the length of the CC number to generate.
	 * Typically 13 or	16
		*/
		private static string CreateFakeCreditCardNumber(string prefix, int length)
		{
			string ccnumber = prefix;

			while (ccnumber.Length < (length - 1))
			{
				double rnd = (new Random().NextDouble()*1.0f - 0f);

				ccnumber += Math.Floor(rnd*10);

				//sleep so we get a different seed

				Thread.Sleep(20);
			}


			// reverse number and convert to int
         var reversedCCnumberstring = ccnumber.ToCharArray().Reverse();

			var reversedCCnumberList = reversedCCnumberstring.Select(c => Convert.ToInt32(c.ToString()));

			// calculate sum

			int sum = 0;
			int pos = 0;
			int[] reversedCCnumber = reversedCCnumberList.ToArray();

			while (pos < length - 1)
			{
				int odd = reversedCCnumber[pos]*2;

				if (odd > 9)
					odd -= 9;

				sum += odd;

				if (pos != (length - 2))
					sum += reversedCCnumber[pos + 1];

				pos += 2;
			}

			// calculate check digit
			int checkdigit =
				Convert.ToInt32((Math.Floor((decimal) sum/10) + 1)*10 - sum)%10;

			ccnumber += checkdigit;

			return ccnumber;
		}


		public static IEnumerable<string> GetCreditCardNumbers(string[] prefixList, int length,
		                                          int howMany)
		{
			var result = new Stack<string>();

			for (int i = 0; i < howMany; i++)
			{
				int randomPrefix = new Random().Next(0, prefixList.Length - 1);
	
				if(randomPrefix>1)
				{
					randomPrefix--;
				}

				string ccnumber = prefixList[randomPrefix];

				result.Push(CreateFakeCreditCardNumber(ccnumber, length));
			}

			return result;
		}


		public static IEnumerable<string> GenerateMasterCardNumbers(int howMany)
		{
			return GetCreditCardNumbers(MASTERCARD_PREFIX_LIST, 16, howMany);
		}


		public static string GenerateMasterCardNumber()
		{
			return GetCreditCardNumbers(MASTERCARD_PREFIX_LIST, 16, 1).First();
		}

		public static bool IsValidCreditCardNumber(string creditCardNumber)
		{
			try
			{
				var reversedNumber = creditCardNumber.ToCharArray().Reverse();
				
				int mod10Count = 0;
				for (int i = 0; i < reversedNumber.Count(); i++)
				{
					int augend = Convert.ToInt32(reversedNumber.ElementAt(i).ToString());

					if (((i + 1)%2) == 0)
					{
						string productstring = (augend*2).ToString();
						augend = 0;
						for (int j = 0; j < productstring.Length; j++)
						{
							augend += Convert.ToInt32(productstring.ElementAt(j).ToString());
						}
					}
					mod10Count += augend;
				}

				if ((mod10Count%10) == 0)
				{
					return true;
				}
			}
			catch
			{
				return false;
			}
			return false;
		}
	}
}

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