using System;
using System.Runtime.InteropServices;
using System.ComponentModel;

namespace JavaScienceCrypto{

public class Win32 {

/* BOOL WINAPI CryptGenRandom(
  HCRYPTPROV hProv,
  DWORD dwLen,
  BYTE* pbBuffer );  
*/

 [DllImport("advapi32.dll", SetLastError=true)]
    public static extern bool CryptGenRandom(
	IntPtr hProv,
	uint dwLen,
	 [In, Out] byte[] pbBuffer) ;


/*BOOL WINAPI CryptAcquireContext(
  HCRYPTPROV* phProv,
  LPCTSTR pszContainer,
  LPCTSTR pszProvider,
  DWORD dwProvType,
  DWORD dwFlags);
*/

 [DllImport("advapi32.dll", CharSet=CharSet.Auto, SetLastError=true)]
    public static extern bool CryptAcquireContext(
	ref IntPtr hProv,
	string pszContainer,
	string pszProvider,
	uint dwProvType,
	uint dwFlags) ;


/*BOOL WINAPI CryptReleaseContext(
  HCRYPTPROV hProv,
  DWORD dwFlags);
*/

 [DllImport("advapi32.dll", SetLastError=true)]
    public static extern bool CryptReleaseContext(
	IntPtr hProv,
	uint dwFlags) ;
}

public class RandomPinvoke {
 const String title = "RandomPinvoke";
 const uint PROV_RSA_FULL   	= 0x00000001;
 const uint CRYPT_VERIFYCONTEXT = 0xF0000000; //no private key access required

   public static void Main() {
	String[] args = Environment.GetCommandLineArgs();
	if(args.Length<2){
	 Console.WriteLine("Usage:  {0}  [int from 5 to 5000]", title);
	 return;
	 }
	String fname = args[1];
	int numbytes=0;
	try{
	 numbytes = Int32.Parse(args[1]);
	 }
	catch(FormatException fexc){
	 Console.WriteLine("Argument not a valid integer");
	 return;
	 }
	catch(Exception exc){
	 Console.WriteLine("Problem parsing argument {0}\n{1}", args[1], exc);
	 return;
	}

    byte[] ranbytes = GenCryptRandomNumber(numbytes) ;
  if(ranbytes == null) {
	Console.WriteLine("Couldn't get random bytes");
	return;
	}
  Console.WriteLine("------------- Random Bytes[{0}]: ----------------------", numbytes);
  for(int i=1; i<=ranbytes.Length; i++){	
	Console.Write("{0:x2}  ", ranbytes[i-1]) ;
	if(i%16 == 0)
	 Console.WriteLine("");
	}
  Console.WriteLine("\n-------------------------------------------------------");

}


 private static byte[] GenCryptRandomNumber(int ranbytes){
    if(ranbytes<5 || ranbytes>5000)  //limit range
	return null;

    byte[] randata = new byte[ranbytes];
    for(int j=0; j<ranbytes; j++)
	randata[j] = 0;

    String provider = null ;	//can use null, for default provider
    String container = null;   //required for crypt_verifycontext 
    uint type  = PROV_RSA_FULL ;
    uint flags = CRYPT_VERIFYCONTEXT ; //no private key access required
    IntPtr hProv = IntPtr.Zero;  

    bool gotcsp = Win32.CryptAcquireContext(ref hProv, container, provider, type, flags);
   if (!gotcsp){
	showWin32Error(Marshal.GetLastWin32Error());
	return null ;
	}
   else
	Console.WriteLine("Got handle to CSP:  hProv 0x{0:X}", hProv.ToInt32());
  if(!Win32.CryptGenRandom(hProv, (uint)ranbytes, randata)){
	showWin32Error(Marshal.GetLastWin32Error());
	Console.WriteLine("Failed to get random bytes!");
	}
  if (hProv != IntPtr.Zero)
	Win32.CryptReleaseContext(hProv,0) ;

   return randata ;
 }

 private static void showWin32Error(int errorcode){
       Win32Exception myEx=new Win32Exception(errorcode);
       Console.WriteLine("Error code:\t 0x{0:X}", myEx.ErrorCode);
       Console.WriteLine("Error message:\t " + myEx.Message);
 }

}
}