Encrypting a file with 3 passwords [SOLVED]

Question

Hi. This is kind of an unusual problem. I am having difficulty encrypting a file using 3 passwords. I am attempting to wrap one CryptoStream around two other CryptoStreams, but when I write the file to the disk, it seems to become corrupted, and the padding cannot be completely removed. Why would this be happening? EDIT: This was SOLVED. It turned out to simply be a server filesystem problem. It was fixed by repairing the virtual disk file.

Edit: Here's some sample code

 public static Stream Encrypt(Stream source, int delcount, params keyPair[] cryptInfo)
    {

        Stream prevStream = source;
        foreach (keyPair et in cryptInfo)
        {
            Rijndael mydale = Rijndael.Create();
            mydale.BlockSize = 256;
            mydale.KeySize = 256;
            mydale.IV = et.IV;
            mydale.Key = et.key;

            CryptoStream mystream = new CryptoStream(prevStream, mydale.CreateEncryptor(), CryptoStreamMode.Write);
            prevStream = mystream;
        }
        return prevStream;

}

Here's the full program Program.cs

class Program
{
    static string opcode = "test";
    static string IDCID = "an ID";
    static string password = "A strong password";
    static void Main(string[] args)
    {
        if (Console.ReadLine() == "encrypt")
        {
            Stream thestream = File.Open(Environment.CurrentDirectory + "\\sample.txt", FileMode.Create, FileAccess.ReadWrite);

            PasswordDeriveBytes mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes(opcode), Encoding.ASCII.GetBytes(opcode));
            byte[] key = mybytes.GetBytes(32);
            mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes((IDCID.Length + password.Length + opcode.Length * 15).ToString()), Encoding.ASCII.GetBytes((IDCID.Length + password.Length + 5 + opcode.Length * 24).ToString()));
            byte[] IV = mybytes.GetBytes(32);
            keyPair mypair = new GlobalGridCore.keyPair(IV, key);
            mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes(password), Encoding.ASCII.GetBytes(password));
            key = mybytes.GetBytes(32);
            mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes((IDCID.Length + password.Length + opcode.Length * 9).ToString()), Encoding.ASCII.GetBytes((IDCID.Length + password.Length + 7 + opcode.Length * 24).ToString()));
            IV = mybytes.GetBytes(32);
            keyPair secondpair = new keyPair(IV, key);
            mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes(IDCID), Encoding.ASCII.GetBytes(IDCID));
            key = mybytes.GetBytes(32);
            mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes((IDCID.Length + password.Length + opcode.Length * 2).ToString()), Encoding.ASCII.GetBytes((IDCID.Length + password.Length + 14 + opcode.Length * 7).ToString()));
            IV = mybytes.GetBytes(32);
            keyPair thirdpair = new keyPair(IV, key);
            keyPair[] list = new keyPair[] { mypair, secondpair, thirdpair };
            thestream = gridCrypto.Encrypt(thestream, 0, list);
            BinaryWriter mywriter = new BinaryWriter(thestream);
            mywriter.Write("ehlo");
            mywriter.Write(new byte[512]);
            mywriter.Flush();
        }
        else
        {
            Stream thestream = File.Open(Environment.CurrentDirectory + "\\sample.txt", FileMode.Open, FileAccess.ReadWrite);

            PasswordDeriveBytes mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes(opcode), Encoding.ASCII.GetBytes(opcode));
            byte[] key = mybytes.GetBytes(32);
            mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes((IDCID.Length + password.Length + opcode.Length * 15).ToString()), Encoding.ASCII.GetBytes((IDCID.Length + password.Length + 5 + opcode.Length * 24).ToString()));
            byte[] IV = mybytes.GetBytes(32);
            keyPair mypair = new GlobalGridCore.keyPair(IV, key);
            mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes(password), Encoding.ASCII.GetBytes(password));
            key = mybytes.GetBytes(32);
            mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes((IDCID.Length + password.Length + opcode.Length * 9).ToString()), Encoding.ASCII.GetBytes((IDCID.Length + password.Length + 7 + opcode.Length * 24).ToString()));
            IV = mybytes.GetBytes(32);
            keyPair secondpair = new keyPair(IV, key);
            mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes(IDCID), Encoding.ASCII.GetBytes(IDCID));
            key = mybytes.GetBytes(32);
            mybytes = new PasswordDeriveBytes(Encoding.Unicode.GetBytes((IDCID.Length + password.Length + opcode.Length * 2).ToString()), Encoding.ASCII.GetBytes((IDCID.Length + password.Length + 14 + opcode.Length * 7).ToString()));
            IV = mybytes.GetBytes(32);
            keyPair thirdpair = new keyPair(IV, key);
            keyPair[] list = new keyPair[] { mypair, secondpair, thirdpair };
            thestream = gridCrypto.Decrypt(thestream, list);
          BinaryReader myreader = new BinaryReader(thestream);
          Console.WriteLine(myreader.ReadString());
          Console.ReadLine();
        }

    }
}

cryptDriver.cs

abstract class gridCrypto
{
    /// <summary>
    /// Decrypts the input stream to the output stream
    /// </summary>
    /// <param name="source">I</param>
    /// <param name="dest">O</param>
    /// <param name="cryptInfo">U</param>
    public static Stream Decrypt(Stream source, params keyPair[] cryptInfo)
    {
        Stream prevStream = source;
        foreach (keyPair et in cryptInfo)
        {
            Rijndael mydale = Rijndael.Create();
            mydale.BlockSize = 256;
            mydale.KeySize = 256;
            mydale.IV = et.IV;
            mydale.Key = et.key;
            CryptoStream mystream = new CryptoStream(prevStream, mydale.CreateDecryptor(), CryptoStreamMode.Read);
            prevStream = mystream;
        }
        return prevStream;
    }
   /// <summary>
   /// Encrypts the input stream and securely deletes the input file with the specified number of passes. The source stream MUST have length
   /// </summary>
   /// <param name="source">The source stream (to be deleted)</param>
   /// <param name="dest">The destination stream</param>
   /// <param name="delcount">The number of passes to erase the file</param>
   /// <param name="cryptInfo">Crypto stuff</param>
    public static Stream Encrypt(Stream source, int delcount, params keyPair[] cryptInfo)
    {

        Stream prevStream = source;
        foreach (keyPair et in cryptInfo)
        {
            Rijndael mydale = Rijndael.Create();
            mydale.BlockSize = 256;
            mydale.KeySize = 256;
            mydale.IV = et.IV;
            mydale.Key = et.key;

            CryptoStream mystream = new CryptoStream(prevStream, mydale.CreateEncryptor(), CryptoStreamMode.Write);
            prevStream = mystream;
        }
        return prevStream;
        //int cpos = 0;
        //while (cpos < delcount)
        //{
        //    source.Position = 0;
        //    while (source.Position < source.Length)
        //    {
        //        if (source.Length - source.Position > 512)
        //        {
        //            Random mrand = new Random();

        //            byte[] thearray = new byte[512];
        //            mrand.NextBytes(thearray);
        //            source.Write(thearray, 0, thearray.Length);
        //        }
        //        else
        //        {
        //            Random mrand = new Random();

        //            byte[] thearray = new byte[source.Length-source.Position];
        //            mrand.NextBytes(thearray);
        //            source.Write(thearray, 0, thearray.Length);
        //            source.Flush();
        //        }
        //    }
        //    cpos += 1;
        //}
    }
}
class keyPair
{
    public byte[] IV;
    public byte[] key;
    public keyPair(byte[] InitializationVector, byte[] Key)
    {
        IV = InitializationVector;
        key = Key;
    }
}

The code to delete the file is commented out and is not used in the program.

Answer 1

Are you sure that the new CryptoStream constructor does not spawn any thread?

Are you sure that when you do prevStream = mystream the newly created mystream has actually finished writing?

Perhaps you need to "flush" the stream first and make sure that the call has completed before assigning it to the older object. I do not know the library, but this looks like a race condition to me.

Answer 2

Why not just encrypt them to an array of bytes, then run those bytes through another algorithm.

If you design it well then you can have n-number of encryption algorithms, and you can embed one inside the other if you desire.

But, if you go want go your route then you may want to break it up into separate steps for testing, to see where the problem may be.

So, you would first encrypt with one algorithm, then immediately decrypt, then use two, then three.

You should have a unit test for this, so that you can test with a short, then a long message, to make certain that you aren't having a problem with message size.

Answer 3

I believe the problem is that you do not use the Write method of the CryptoStream where encryption happens. You just initialise them which sets the stream that you will be writing to and not reading from. Have a look at this sample:

http://msdn.microsoft.com/en-us/library/k1f992c1.aspx

which says:

    // Create or open the specified file.
        FileStream fStream = File.Open(FileName, FileMode.OpenOrCreate);

        // Create a new Rijndael object.
        Rijndael RijndaelAlg = Rijndael.Create();

        // Create a CryptoStream using the FileStream 
        // and the passed key and initialization vector (IV).
        CryptoStream cStream = new CryptoStream(fStream,
            RijndaelAlg.CreateEncryptor(Key, IV),
            CryptoStreamMode.Write);

        // Create a StreamWriter using the CryptoStream.
        StreamWriter sWriter = new StreamWriter(cStream);

        try
        {
            // Write the data to the stream 
            // to encrypt it.
            sWriter.WriteLine(Data);
        }
        .....

I personally always use TransfromBlock because I know what my in and out bytes are.

Answer 4

If I understand correctly, your passwords have to be used in reversed order when decrypting.

Try this in the decrypt-part of your Program.cs:

  keyPair[] list = new keyPair[] { thirdpair, secondpair, mypair };
  thestream = gridCrypto.Decrypt(thestream, list);

Answer 5

You're not disposing of your stream. Insert this into your encryption test code:

thestream.Dispose();

or (preferably) use a using statement to open the file:

using (Stream stream = File.Open(...))
{
}

at the end, and it works.

You should (almost) always use using statements when using streams, to make sure they're closed properly. In the case of crypto streams, closing the stream also writes the final block.

I'm somewhat surprised you don't need to reverse the order of the keys... but the key creation code is sufficiently obscure that I don't really want to explore it much further :(

Answer 6

It was a filesystem problem on the server. It was fixed after the server admin ran an FSRepair on the server.