Having problems with encryption..

[a perfect circle]

I'm trying to send an encrypted string in a UDP packet from my C++ application, and recieve and decrypt it in my C# application. The encryption code in the C++ application works fine, I have no problem encrypting and decrypting it in my C++ app. However, I have no idea if I can or how to decrypt the data in my C# app using the crypo classes C# has. So I decided to try making a DLL in C++ with the encrypt/decrypt functions, and try to import and use it in my C# app. However, when I try to call the functions, the app crashes for me.

Here is the import code I'm using:

        // import EncryptData()
        [DllImport("Rjindael.dll", CharSet = CharSet.Auto, EntryPoint = "EncryptData")]
        public static extern void EncryptData( string key, string input, string result, int n, int mode );

        // import DecryptData()
        [DllImport("Rjindael.dll", CharSet = CharSet.Auto, EntryPoint = "DecryptData")]
        public static extern void DecryptData( string key, string input, string result, int n, int mode);

I know the functions are being exporter properly, I checked with PE explorer. I'm also using a module definition file to export the function names correctly.

My testing function:

        private void button1_Click(object sender, EventArgs e)
        {
            string final_key = "12345678901234567890123456789012"; // 32 bytes
            string src = "asd 123"; // input

            string encrypted = ""; // output
            try
            {
                EncryptData(final_key, src, encrypted, src.Length, 1);
                txtLog.AppendText(encrypted);
            }
            catch (Exception ex) { txtLog.AppendText("Error: " + ex.ToString() + "\n"); }

        }

I don't know much about encryption or how to import C++ code in to C#.

The C++ functions I'm exporting are:
EncryptData:

RJINDAEL_API void EncryptData( char const* key, char const* input, char const* result, size_t n, int mode )
{
	try {
		// initialize the crypto key
		CRijndael crypt;
		crypt.MakeKey(key, CRijndael::sm_chain0, 32, 32);

		char szDataIn [ENCRYPTION_BUFFERSZ  ];
		char szDataOut[ENCRYPTION_BUFFERSZ+1];

		// validate the mode
		if( mode < 0 || mode > 2 )
			mode = CRijndael::CBC;

		// copy data into the buffer
		strncpy( szDataIn, input, sizeof( szDataIn ) );

		// clear the output buffer
		memset( szDataOut, 0, sizeof(szDataOut) );

		// encrypt the data
		crypt.Encrypt( szDataIn, szDataOut, ENCRYPTION_BUFFERSZ-1, mode );

		// copy data to the output buffer
		strncpy( (char*)result, szDataOut, n );
	}
	catch( exception& roEx)
	{
		result = NULL;
		return;
	}
}

DecryptData:

RJINDAEL_API void DecryptData( char const* key, char const* input, char const* result, size_t n, int mode )
{
	try {
		// initialize the crypto key
		CRijndael crypt;
		crypt.MakeKey(key, CRijndael::sm_chain0, 32, 32);

		char szDataIn [ENCRYPTION_BUFFERSZ  ];
		char szDataOut[ENCRYPTION_BUFFERSZ+1];

		// validate the mode
		if( mode < 0 || mode > 2 )
			mode = CRijndael::CBC;

		// copy data into the buffer
		strncpy( szDataIn, input, sizeof( szDataIn ) );

		// clear the output buffer
		memset( szDataOut, 0, sizeof(szDataOut) );

		// decrypt the data
		crypt.ResetChain();
		crypt.Decrypt( szDataIn, szDataOut, ENCRYPTION_BUFFERSZ-1, mode );

		// copy data to the output buffer
		strncpy( (char*)result, szDataOut, n );
	}
	catch( exception& roEx)
	{
		result = NULL;
		return;
	}
}

The dll code can be found in the following links:
Rjindael.cpp:
http://pastebin.com/vQ1z2Dnf

Rjindael.h:
http://pastebin.com/2nRtLErH

The functions I'm exporting / trying to import are at the bottom of the Rjindael.cpp. Also, the class isn't mine, I found it on the web and modified it a bit. I don't remember the link or I'd just post it instead. Sorry. :\



So, what am I doing wrong? What am I missing? How do I make the C# app use the DLL properly?


Thanks in advance!

[Techno]

when you say "it crashes" - what error do you get?
why dont you do all the encryption/decryption in C#? There are plenty of encryption classes in .NET. Reading the API docs on MSDN or simply googling for the algo you want will present you with results

[a perfect circle]

Hmm, I modified the function a bit so it returns the data instead.

C# code:

        // import EncryptData()
        [DllImport("Rjindael.dll", CharSet = CharSet.Auto, EntryPoint = "EncryptData")]
        public static extern string EncryptData( string key, string input, int mode );

        // import DecryptData()
        [DllImport("Rjindael.dll", CharSet = CharSet.Auto, EntryPoint = "DecryptData")]
        public static extern string DecryptData(string key, string input, int mode);

        private void button1_Click(object sender, EventArgs e)
        {
            string final_key = "12345678901234567890123456789012"; // 32 bytes
            string src = "asd 123"; // input

            
            try
            {
                string encrypted = EncryptData(final_key, src, 1);
                txtLog.AppendText(encrypted);
            }
            catch (Exception ex) { txtLog.AppendText("Error: " + ex.ToString() + "\n"); }
        }

DLL code:

RJINDAEL_API char* EncryptData( char const* key, char const* input, int mode )
{
	try {
		// initialize the crypto key
		CRijndael crypt;
		crypt.MakeKey(key, CRijndael::sm_chain0, 32, 32);

		char szDataIn [ENCRYPTION_BUFFERSZ  ];
		char szDataOut[ENCRYPTION_BUFFERSZ+1];

		// validate the mode
		if( mode < 0 || mode > 2 )
			mode = CRijndael::CBC;

		// copy data into the buffer
		strncpy( szDataIn, input, sizeof( szDataIn ) );

		// clear the output buffer
		memset( szDataOut, 0, sizeof(szDataOut) );

		// encrypt the data
		crypt.Encrypt( szDataIn, szDataOut, ENCRYPTION_BUFFERSZ-1, mode );

		// copy data to the output buffer
		//strncpy( (char*)result, szDataOut, n );
		return (char*)szDataOut;
	}
	catch( exception& roEx)
	{
		// return NULL if something happens
		return NULL;
	}
}
RJINDAEL_API char* DecryptData( char const* key, char const* input, int mode )
{
	try {
		// initialize the crypto key
		CRijndael crypt;
		crypt.MakeKey(key, CRijndael::sm_chain0, 32, 32);

		char szDataIn [ENCRYPTION_BUFFERSZ  ];
		char szDataOut[ENCRYPTION_BUFFERSZ+1];

		// validate the mode
		if( mode < 0 || mode > 2 )
			mode = CRijndael::CBC;

		// copy data into the buffer
		strncpy( szDataIn, input, sizeof( szDataIn ) );

		// clear the output buffer
		memset( szDataOut, 0, sizeof(szDataOut) );

		// decrypt the data
		crypt.ResetChain();
		crypt.Decrypt( szDataIn, szDataOut, ENCRYPTION_BUFFERSZ-1, mode );

		// copy data to the output buffer
		//strncpy( (char*)result, szDataOut, n );
		return (char*)szDataOut;
	}
	catch( exception& roEx)
	{
		// return NULL if something happens
		return NULL;
	}
}

Now it gives me the following error in the log window:

Error: System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
   at njka_testing.frmMain.EncryptData(String key, String input, Int32 mode)
   at njka_testing.frmMain.button1_Click(Object sender, EventArgs e) in C:\Users\bored\Documents\Visual Studio 2010\Projects\njka_testing\njka_testing\Form1.cs:line 484

I tried changing the return data type to byte[] instead of string, but got this error:

Error: System.Runtime.InteropServices.MarshalDirectiveException: Cannot marshal 'return value': Invalid managed/unmanaged type combination.

Am I using a wrong datatype somewhere? What am I doing wrong now? ...

[Techno]

problem maybe in your encryption/decryption code in C++


here is the MSDN doc FULL with code on encryption/decryption in C#:

http://msdn.microsoft.com/en-us/libr...elmanaged.aspx

[a perfect circle]

The encryption code works fine. I encrypted a string, displayed it in hex, and decrypted it successfully. Will I be able to decrypt the data using the Rijndael Managed class you linked me? All the examples and other stuff I found while googling it show that I need an IV key, and the class I've been using in C++ doesn't mention an IV anywhere.


Is it possible to use that RijndaelManaged class in C++ as well?

[Techno]

yes it is but it would be managed code and use .NET Framework. what difference would it make if you used the .NET Framework and develop in either C++ or C#? it wouldnt really as you would be using the .NET Libraries.

have you tried using the example and forgetting about the idea of the fact that there is an IV key?

http://msdn.microsoft.com/en-us/libr....rijndael.aspx

it uses the Generated IV key so you dont need to worry about creating your own and storing it somewhere

[Evil_Giraffe]

It's been a while since I had to look at a crypto implementation, but I think the IV is what the C++ class calls the "chain"? (passed in to the MakeKey method)