Question

I get “Length of the data to decrypt is invalid.” exception when i try to decrypt a memory stream. I am beginner, cant figure out whats wrong. whats wrong?

public bool EncryptStream()
    {

        string password = @"myKey123"; // Your Key Here
        UnicodeEncoding UE = new UnicodeEncoding();
        byte[] key = UE.GetBytes(password);

        s_EncryptedStream = new MemoryStream();
        int NoOfBytes;
        byte[] b_Buffer = new byte[8192];

        s_MemoryStream.Seek(0, SeekOrigin.Begin);

        RijndaelManaged RMCrypto = new RijndaelManaged();

        s_CrytpoStream = new CryptoStream(s_EncryptedStream,
            RMCrypto.CreateEncryptor(key, key),
            CryptoStreamMode.Write);

        while (s_MemoryStream.Length < s_MemoryStream.Position)
        {
            NoOfBytes = s_MemoryStream.Read(b_Buffer, 0, 8192);
            s_CrytpoStream.Write(b_Buffer, 0, NoOfBytes);
        }

        s_MemoryStream.Seek(0, SeekOrigin.Begin);

        while (s_EncryptedStream.Position < s_EncryptedStream.Length)
        {
            NoOfBytes = s_EncryptedStream.Read(b_Buffer, 0, 8192);
            s_MemoryStream.Write(b_Buffer, 0, NoOfBytes);

        }
        s_CrytpoStream.Flush();
        s_CrytpoStream.Close();

        return true;

    }


    public bool DecryptStream()
    {


        string password = @"myKey123"; // Your Key Here

        UnicodeEncoding UE = new UnicodeEncoding();
        byte[] key = UE.GetBytes(password);

        int NoOfBytes;
        byte[] b_Buffer = new byte[8192];

        s_DecryptedStream = new MemoryStream();


        RijndaelManaged RMCrypto = new RijndaelManaged();

        s_CrytpoStream = new CryptoStream(s_MemoryStream,
            RMCrypto.CreateDecryptor(key, key),
            CryptoStreamMode.Read);

        s_MemoryStream.Seek(0, SeekOrigin.Begin);

        while (s_MemoryStream.Length > s_MemoryStream.Position)
        {
            NoOfBytes = s_CrytpoStream.Read(b_Buffer, 0, 8192);
            s_DecryptedStream.Write(b_Buffer, 0, NoOfBytes);
        }

        s_DecryptedStream.Seek(0, SeekOrigin.Begin);
        s_MemoryStream.Seek(0, SeekOrigin.Begin);

        while (s_DecryptedStream.Position < s_DecryptedStream.Length)
        {
            NoOfBytes = s_DecryptedStream.Read(b_Buffer, 0, 8192);
            s_MemoryStream.Write(b_Buffer, 0, NoOfBytes);

        }

        s_CrytpoStream.Flush();
        s_CrytpoStream.Close();

        return true;

    }

Answer 1

For a start, this while loop condition is never right:

while (s_MemoryStream.Length < s_MemoryStream.Position)

How can the position be beyond the length?

Rather than using the length of a stream, the usual pattern to copy a stream is to read repeatedly until the value returned isn’t positive. As you’re doing that twice in this code anyway, you might as well encapsulate it:

public static void CopyStream(Stream input, Stream output)
{
    byte[] buffer = new byte[8192];
    int read;
    while ( (read = input.Read(buffer, 0, buffer.Length)) > 0)
    {
        output.Write(buffer, 0, read);
    }
}

It’s also best to use using statements to clean up strings. Additionally, the Encoding.Unicode property means you don’t have to create a new UnicodeEncoding yourself. Also, I generally find that setting the Position property is more readable than using Seek. Finally, there’s no point in a method returning a value if it’s always going to be true. So, your code would become:

public void EncryptStream()
{
    string password = @"myKey123"; // Your Key Here
    byte[] key = Encoding.Unicode.GetBytes(password);

    s_EncryptedStream = new MemoryStream();
    s_MemoryStream.Position = 0;

    RijndaelManaged RMCrypto = new RijndaelManaged();

    using (Stream crytpoStream = new CryptoStream(s_EncryptedStream,
        RMCrypto.CreateEncryptor(key, key),
        CryptoStreamMode.Write))
    {
        CopyStream(s_MemoryStream, cryptoStream);
    }

    s_MemoryStream.Position = 0;
    s_EncryptedStream.Position = 0;
    CopyStream(s_EncryptedStream, s_MemoryStream);
}

public void DecryptStream()
{
    string password = @"myKey123"; // Your Key Here
    byte[] key = Encoding.Unicode.GetBytes(password);

    s_DecryptedStream = new MemoryStream();
    s_MemoryStream.Position = 0;

    RijndaelManaged RMCrypto = new RijndaelManaged();

    using (Stream crytpoStream = new CryptoStream(s_MemoryStream,
        RMCrypto.CreateDecryptor(key, key),
        CryptoStreamMode.Read))
    {
        CopyStream(cryptoStream, s_DecryptedStream);
    }

    s_DecryptedStream.Position = 0;
    s_MemoryStream.Position = 0;

    CopyStream(s_DecryptedStream, s_MemoryStream);
}

Even after amending this code, it feels like you’ve got way too many non-local variables here. I can’t see why any of this should be in instance variables. Make the stream to be encrypted or decrypted a parameter (along with the password) and return a memory stream with the encrypted/decrypted data in, or just a byte array.