using System;

using System.Security.Cryptography;

using System.Text;

using System.Collections.Generic;

using System.Linq;

​

​

public class Program

{

    const int REPETITIONS = 1000000;

        const int KEY_SIZE = 32;

​

        static void Main(string[] args)

        {

            Console.WriteLine("Original BIASED implementation");

            PerformTest(REPETITIONS, KEY_SIZE, KeyGenerator.GetUniqueKeyOriginal_BIASED);

​

            Console.WriteLine("Updated implementation");

            PerformTest(REPETITIONS, KEY_SIZE, KeyGenerator.GetUniqueKey);

            Console.ReadKey();

        }

​

        static void PerformTest(int repetitions, int keySize, Func<int, string> generator)

        {

            Dictionary<char, int> counts = new Dictionary<char, int>();

            foreach (var ch in KeyGenerator.chars) counts.Add(ch, 0);

​

            for (int i = 0; i < REPETITIONS; i++)

            {

                var key = generator(KEY_SIZE); 

                foreach (var ch in key) counts[ch]++;

            }

​

            int totalChars = counts.Values.Sum();

            foreach (var ch in KeyGenerator.chars)

            {

                Console.WriteLine($"{ch}: {(100.0 * counts[ch] / totalChars).ToString("#.000")}%");

            }

        }

}

​

​

​

​

​

    public class KeyGenerator

    {

        internal static readonly char[] chars =

            "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890".ToCharArray(); 

​

        public static string GetUniqueKey(int size)

        {            

            byte[] data = new byte[4*size];

            using (RNGCryptoServiceProvider crypto = new RNGCryptoServiceProvider())

            {

                crypto.GetBytes(data);

            }

            StringBuilder result = new StringBuilder(size);

            for (int i = 0; i < size; i++)

            {

                var rnd = BitConverter.ToUInt32(data, i * 4);

                var idx = rnd % chars.Length;

​

                result.Append(chars[idx]);

            }

​

            return result.ToString();

        }

​

        public static string GetUniqueKeyOriginal_BIASED(int size)

        {

            char[] chars =

                "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890".ToCharArray();

            byte[] data = new byte[size];

            using (RNGCryptoServiceProvider crypto = new RNGCryptoServiceProvider())

            {

                crypto.GetBytes(data);

            }

            StringBuilder result = new StringBuilder(size);

            foreach (byte b in data)

            {

                result.Append(chars[b % (chars.Length)]);

            }

            return result.ToString();

        }

    }

​