C# - SHA-1 Hash einer Datei erzeugen

using System.Security.Cryptography 
using System.Text 
using Imports System.IO 


private string SHA1StringHash(string strString) 
{ 
  System.Security.Cryptography.SHA1CryptoServiceProvider SHA1 = new System.Security.Cryptography.SHA1CryptoServiceProvider();
  byte[] Hash; 
  string Result = string.Empty; 
  string Tmp =string.Empty; 

  FileStream FN = new FileStream(strString, FileMode.Open, FileAccess.Read, FileShare.Read, 8192); 
  SHA1.ComputeHash(FN); 
  FN.Close(); 

  Hash = SHA1.Hash; 
  for (int i = 0; i < Hash.Length; i++) 
  { 
    Tmp = Convert.ToString(Hash[i],16); 
    if (Tmp.Length == 1) 
      Tmp = "0" + Tmp; 
    Result += Tmp; 
  } 
  return Result; 
}