C# uses RNGCryptoServiceProvider to generate strong random strings

1  using System.Security.Cryptography;
 2  sealed  class RNGCryptoRandomService
 3  {
 4      private  static RNGCryptoServiceProvider _random = new RNGCryptoServiceProvider();
 5  
6      public  static  string GetRandomString( int stringlength)
 7      {
 8          return GetRandomString( null , stringlength);
 9      }
 10  
11      // Get a random string of length stringLength, with key as alphabet 
12      public  static  string GetRandomString(string key, int stringLength)
13     {
14         if (key == null || key.Length < 8)
15         {
16             key = "abcdefghijklmnopqrstuvwxyz1234567890";
17         }
18 
19         int length = key.Length;
20         StringBuilder randomString = new StringBuilder(length);
21         for (int i = 0; i < stringLength; ++i)
22         {
23             randomString.Append(key[SetRandomSeeds(length)]);
24         }
25 
26         return randomString.ToString();
27     }
28 
29     private static int SetRandomSeeds(int length)
30     {
31         decimal maxValue = (decimal)long.MaxValue;
32         byte[] array = new byte[8];
33         _random.GetBytes(array);
34 
35         return (int)(Math.Abs(BitConverter.ToInt64(array, 0)) / maxValue * length);
36     }
37 }