//*******************************************************
// DecEnvelop
// Enveloped File Decryptor
//
// Copyright (C) 2003.  Michel I. Gallant
//********************************************************
//
// DecEnvelop.cs
//
// Uses P/Invoke to CryptoAPI simplified message function
//     CryptDecryptMessage()
// Input file can be binary or b64 CMS/pkcs#7 format
//********************************************************
using System;
using System.IO;
using System.Runtime.InteropServices;
using System.ComponentModel;
using System.Reflection;
using System.Text;

namespace JavaScience
{
public class Win32 {
 [DllImport("crypt32.dll", CharSet=CharSet.Auto, SetLastError=true)]
    public static extern IntPtr CertOpenSystemStore(
        IntPtr hCryptProv,
        string storename) ;

 [DllImport("crypt32.dll", SetLastError=true)]
    public static extern bool CertCloseStore(
        IntPtr hCertStore,
        uint dwFlags) ;

 [DllImport("crypt32.dll", SetLastError=true)]
  public static extern bool CryptDecryptMessage(
   ref CRYPT_DECRYPT_MESSAGE_PARA pDecryptPara,
   byte[] pbEncryptedBlob,
   int cbEncryptedBlob,
   [In, Out] byte[] pbDecrypted,
   ref int pcbDecrypted,
   IntPtr ppXchgCert);
}



 [StructLayout(LayoutKind.Sequential)]
  public struct CRYPT_DECRYPT_MESSAGE_PARA
  {
        public int cbSize;
        public uint dwMsgAndCertEncodingType;
        public int cCertStore;
        public IntPtr rghCertStore;
        //public uint dwFlags;
  }
//--Note: CRYPT_DECRYPT_MESSAGE_PARA.dwFlags only for XP+ OS


public class DecEnvelop {
  const  string MY        = "MY";
  const  string OTHERS    = "AddressBook";
  const  uint PKCS_7_ASN_ENCODING	= 0x00010000;
  const  uint X509_ASN_ENCODING		= 0x00000001;
  static uint MY_ENCODING_TYPE	= PKCS_7_ASN_ENCODING | X509_ASN_ENCODING ;
  static bool verbose = false;  

 public static void Main(String[] args){ 
  String sysstore = MY;
  IntPtr hSysStore  = IntPtr.Zero;
  IntPtr hCertCntxt = IntPtr.Zero;
  IntPtr pProvInfo  = IntPtr.Zero;
  IntPtr pexcKey = IntPtr.Zero;
  String filename = null;
  String outfile = null;

 if(args.Length < 2){
	 Usage();
	 return;
	}
 filename = args[0];
 outfile  = args[1];

 if(!File.Exists(filename)){
  Console.WriteLine("File {0} not found. ", filename);
  return;
 }

 if(File.Exists(outfile)){
  Console.Write("File {0} already exists.\nOverwrite output file?  ", outfile);
  string resp = Console.ReadLine().Trim().ToLower();
  if( !(resp.Equals("y") || resp.Equals("yes")) )
   return;
 }

//------- Get encoded enveloped data from file -----
 byte[] envdata = DecEnvelop.GetFileBytes(filename);
 byte[] denvbytes;

 if(verbose)
  Console.WriteLine("File has {0} bytes",envdata.Length);

 hSysStore = Win32.CertOpenSystemStore(IntPtr.Zero, sysstore) ;
 if(hSysStore == IntPtr.Zero) {
  Console.WriteLine("Couldn't get system store {0}", sysstore);
  return;
 }
 if (verbose)
  Console.WriteLine("Store Handle:\t{0}", hSysStore);

  CRYPT_DECRYPT_MESSAGE_PARA messpara = new CRYPT_DECRYPT_MESSAGE_PARA();
  messpara.cbSize = Marshal.SizeOf(messpara);
  messpara.dwMsgAndCertEncodingType = MY_ENCODING_TYPE;
  messpara.cCertStore = 1;
  messpara.rghCertStore = Marshal.AllocHGlobal(IntPtr.Size); //one cert store pointer
  Marshal.WriteIntPtr(messpara.rghCertStore, hSysStore);

 int decbytes = 0;

//------ if fails, then might be b64 encoded file; try b64 decoding ------------
 if(!Win32.CryptDecryptMessage( ref messpara, envdata, envdata.Length, null, ref decbytes, IntPtr.Zero))
  {
 	ASCIIEncoding ascii = new ASCIIEncoding();
 	String datastr = ascii.GetString(envdata);
	try{
	 envdata = Convert.FromBase64String(datastr);  //try to b64 decode
	}
	catch(System.FormatException){
	 Console.WriteLine("File '{0}' cannot be decrypted", filename);
	 Marshal.FreeHGlobal(messpara.rghCertStore);
	 return;
	}
	if(verbose)
	  Console.WriteLine("Base64 converted size: {0}", envdata.Length);
 }
 
  if(Win32.CryptDecryptMessage( ref messpara, envdata, envdata.Length, null, ref decbytes, IntPtr.Zero))
  {
    if(verbose)
      Console.WriteLine("Bytes allocated: {0}", decbytes);
    denvbytes = new byte[decbytes];
   
    if(Win32.CryptDecryptMessage(ref messpara, envdata, envdata.Length, denvbytes, ref decbytes, IntPtr.Zero))
    {
      Console.WriteLine("Decrypted data: {0} bytes", decbytes);
      PutFileBytes(outfile, denvbytes, decbytes);
      if(verbose)
        DecEnvelop.DisplayBytes(denvbytes);
    }
    else
	Console.WriteLine("Failed to decrypt file (incorrect password?)");
  }
  else{
   Console.WriteLine("Couldn't decrypt file") ; 
   showWin32Error(Marshal.GetLastWin32Error());
  }
  Marshal.FreeHGlobal(messpara.rghCertStore);

 if(hSysStore != IntPtr.Zero)
        Win32.CertCloseStore(hSysStore, 0) ;
 }



 private static byte[] GetFileBytes(String filename){
        if(!File.Exists(filename))
         return null;
        Stream stream=new FileStream(filename,FileMode.Open);
        int datalen = (int)stream.Length;
        byte[] filebytes =new byte[datalen];
        stream.Seek(0,SeekOrigin.Begin);
        stream.Read(filebytes,0,datalen);
        stream.Close();
        return filebytes;
  }


  private static void DisplayBytes(byte[] data) 
  {
	for(int i=1; i<=data.Length; i++){	
	 Console.Write("{0:x2}  ", data[i-1]) ;
	  if(i%16 == 0)
		Console.WriteLine("");
	}
   Console.WriteLine();
 }


 private static void PutFileBytes(String outfile, byte[] data, int bytes) {
  FileStream fs = null;
	if(bytes > data.Length) {
	   Console.WriteLine("Too many bytes");
	   return;
	  }
	try{
	 fs = new FileStream(outfile, FileMode.Create);
	 fs.Write(data, 0, bytes);
	 Console.WriteLine("Wrote file '{0}'", outfile) ;
	}
	catch(Exception e) {
	 Console.WriteLine(e.Message) ; 
	}
	finally {
	 fs.Close();
	}
 }


 private static void Usage() {
   Console.WriteLine("\nUsage:\nDecEnvelop  <envelopedfile>  <out_decrypted_file>");
  }


 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);
 }

}
}