Windows Security: Path Interpretation

I've come across this MSDN article, which talks about how Windows interprets paths:
http://msdn.microsoft.com/en-us/library/aa365247%28v=vs.85%29.aspx

Why is this a security concern?
Let's say you have an application that allows a user to write a file path as input, and to get the content of the file as output. You want to restrict access to a specific file, let's say:

c:\secret location\passwords.txt

This code is a possible way of writing such functionality:

Code:

string GetFile(string path)
{
	if (isok(path))
	{
		return System.IO.File.ReadAllText(path);
	}
	else
	{
		throw new Exception("Access denied");
	}
}

Maybe the best option is limiting the permissions of the application so it can't access the file, but then what about a web server that needs to hide .htaccess from the user but must be able to read it?
So maybe you choose another option - examining the file path.
For example:

Code:

bool isok(string path)
{
	return path != @"c:\secret location\passwords.txt";
	// THIS CODE IS WRONG
}

But then an attacker could use uppercase or mixed to represent the same file:

Code:

GetFile(@"C:\SECRET LOCATION\PASSWORDS.TXT");
GetFile(@"C:\SeCrEt LoCaTiOn\PaSsWoRdS.TxT");

So maybe this might be a possible fix:

Code:

bool isok(string path)
{
	return path.ToLower() != @"c:\secret location\passwords.txt";
	// THIS CODE IS WRONG
}

Unfortunately this code isn't sufficient either, what about:

Code:

GetFile(@"c:\aaaa\..\secret location\passwords.txt");

Note that it works even if aaaa doesn't exist.
This can go on and on. I tried to put some of those "path features" in the following list.

1. Normal: @"c:\secret location\passwords.txt"
2. Upper/lower case: @"C:\Secret Location\Passwords.TxT"
3. Parent directory: @"c:\aaa\..\secret location\passwords.txt"
4. Current directory: @"c:\.\secret location\passwords.txt"
5. Current file: @"c:\secret location\passwords.txt\."
6. Spaces: @"c:\secret location\passwords.txt   "
7. Dots: @"c:\secret location\passwords.txt...."
8. Network share: @"\\localhost\c$\secret location\passwords.txt"
   or <ip_address> or <computer_name> or 127.0.0.1
9. Long path prefix: @"\\?\c:\secret location\passwords.txt"
10. MS-DOS style: @"C:\SECRET~1\PASSWO~1.TXT"
11. Relative path: @"c:secret location\passwords.txt"
    (Works if current directory is c:\, otherwise need to add ..)
12. Win32 device: @"\\.\c:\secret location\passwords.txt"
13. Long UNC: @"\\?\UNC\localhost\c$\secret location\passwords.txt"
14. ADS: @"c:\secret location\passwords.txt::$DATA"
15. Unix style: @"c:/secret location\passwords.txt"

Go on, try some of them!
There are probably many more ways that aren't on that list.
For conclusion, restricting access to a file simply by examining the input path is probably a bad idea. An alternative better solution should be chosen depending on the project requirements.

OpenLayers map + markers + cool info box

I made a little project for my father (in return he pays for my piano lessons).
My father is one of the managers of the folk dance society in Israel. They have a website, where all dancing clubs are listed, including relevant information such as place, time, price, type of music, ...
He wanted a map where someone could see all dancing places near his/her home.
Google Maps would have been a natural choice hadn't they forbidden access to their API specifically for Israel.
I found a great alternative: OpenLayes, which uses data from OpenStreetMap.
I'm all excited because I know nothing about JavaScript and CSS but eventually it worked!
Well, here it is:


Things to notice:

• The info box is half transparent
• It has round corners
• When you click a place, the info box sticks, so you can follow the links

C#: How to bypass firewall

Firewalls like ZoneAlarm are supposed to be able to block outgoing connections of unknown programs. So for example, if I was careless and installed a malware, then at least it won't be able to send my passwords list to someone over the internet.
Couple of years ago I tried to think about how to bypass that, and after a while I came up with this simple trick that works regardless of the firewall software, i.e. it does not alter the firewall.

Many users use Internet Explorer, so usually it has access through the firewall by default. It only remains to take control over it from C#, and that's exactly what I did using this magical API function: ObjectFromLresult. It might be funny to see a trojan horse written entirely using GET requests, but on the other hand it scares me a little bit because for example ZoneAlarm and AVG couldn't detect it.
I wrote a small C# application to prove my point. You can download it from here:
http://www.megaupload.com/?d=9W17LLP4
It has 2 buttons: the first button attempts to make a normal HttpWebRequest, and tells you whether it succeeded or failed. If it failed, then probably your firewall is blocking the application. In that case you may want to try the second button.

This is the code that creates a new Internet Explorer instance and gets the DOM object from it:
(I found it on the internet)

Code:

[DllImport("user32.dll", EntryPoint = "GetClassNameA")]
public static extern int GetClassName(IntPtr hwnd, StringBuilder lpClassName, int nMaxCount);
public delegate int EnumProc(IntPtr hWnd, ref IntPtr lParam);
[DllImport("user32.dll")]
public static extern int EnumChildWindows(IntPtr hWndParent, EnumProc lpEnumFunc, ref  IntPtr lParam);
[DllImport("user32.dll", EntryPoint = "RegisterWindowMessageA")]
public static extern int RegisterWindowMessage(string lpString);
[DllImport("user32.dll", EntryPoint = "SendMessageTimeoutA")]
public static extern int SendMessageTimeout(IntPtr hwnd, int msg, int wParam, int lParam, int fuFlags, int uTimeout, out int lpdwResult);
[DllImport("OLEACC.dll")]
public static extern int ObjectFromLresult(int lResult, ref Guid riid, int wParam, ref IHTMLDocument2 ppvObject);
public const int SMTO_ABORTIFHUNG = 0x2;
public Guid IID_IHTMLDocument = typeof(mshtml.IHTMLDocument).GUID;

public Process process = null;
public IHTMLDocument2 document;

public IHTMLDocument2 documentFromDOM(string url)
{
    process = new Process();
    process.StartInfo.FileName = "iexplore.exe";
    process.StartInfo.WindowStyle = ProcessWindowStyle.Minimized;
    process.StartInfo.Arguments = url;
    process.Start();
    IntPtr hWnd = IntPtr.Zero;
    do
    {
        Thread.Sleep(3000);
    } while ((hWnd = process.MainWindowHandle) == IntPtr.Zero);
    int lngMsg = 0;
    int lRes;
    IntPtr document_hWnd;
    EnumProc proc = new EnumProc(EnumWindows);
    EnumChildWindows(hWnd, proc, ref hWnd);
    if (!hWnd.Equals(IntPtr.Zero))
    {
        lngMsg = RegisterWindowMessage("WM_HTML_GETOBJECT");
        if (lngMsg != 0)
        {
            SendMessageTimeout(hWnd, lngMsg, 0, 0, SMTO_ABORTIFHUNG, 1000, out lRes);
            if (!(bool)(lRes == 0))
            {
                document_hWnd = hWnd;
                int hr = ObjectFromLresult(lRes, ref IID_IHTMLDocument, 0, ref document);
                if (document == null)
                {
                    MessageBox.Show("No IHTMLDocument Found!");
                }
            }
        }
    }
    return document;
}

public int EnumWindows(IntPtr hWnd, ref IntPtr lParam)
{
    int retVal = 1;
    StringBuilder classname = new StringBuilder(128);
    GetClassName(hWnd, classname, classname.Capacity);
    if (classname.ToString() == "Internet Explorer_Server")
    {
        lParam = hWnd;
        retVal = 0;
    }
    return retVal;
}

Notes:
The user can see the Internet Explorer at the taskbar, and the Thread.Sleep is weird, but both can be fixed sometime.

C#: Camera Matrix

I always wanted to know how a 3D engine works. I've used DirectX several times before, but I never quite understood what's going on behind the scene.
So, I decided to write a small naive 3D engine of my own, just to understand how it works.
I studied about the subject, and wrote this engine, which is basically a camera matrix: (no textures or anything)
http://www.megaupload.com/?d=6YON627Z
The only external graphics function I used is the Graphics.DrawLine() function.

What is a Camera Matrix anyway?
It's something that can be used to display 3D objects on our 2D screen.
Think about a real camera like in a 2D movie (not Avatar) - you place it somewhere in the room (translation), it looks towards the scene (rotation), it can zoom in and out (scaling), and it converts the 3D scene to 2D (projection).
From now on we say "translation" instead of "position". Mathematicians are to blame for that.

It's easy to do operations on vectors, why complicate things with Matrices?
One of the main reasons is that matrices can be easily concatenated.
From DirectX MSDN:

One advantage of using matrices is that you can combine the effects of two or more matrices by multiplying them. This means that, to rotate a model and then translate it to some location, you do not need to apply two matrices. Instead, you multiply the rotation and translation matrices to produce a composite matrix that contains all of their effects.

Let me put it this way:
"Using" a 4x4 matrix requires 16 multiplications and 9 additions.
So rotating, which is "using" a rotation matrix, requires 16 multiplications and 9 additions.
And scaling also requires 16 multiplications and 9 additions.
If we do rotating and then scaling it would take 32 multiplications and 18 additions. Translation would takes us up to 48 multiplications and 27 additions, and so on...
BUT, if we concatenate the rotation and scaling matrices, we will get a third matrix that does both operations in half the time (16 multiplications and 9 additions).
In fact, we could concatenate any number of matrices, so the resulting matrix will do all the operations we want in only 16 multiplications and 9 additions.
You might have noticed that we still need to do the concatenation operation which takes a long time, but it's worth it when you design a 3D game with thousands and thousands of objects to scale rotate translate etc. but only a few matrices to concatenate.

Why a Camera Matrix is not 3x3?
In short, because then we can't use it for translation (moving the vectors).
For more details read this fantastic article:
http://www.geometer.org/mathcircles/cghomogen.pdf

C#: Matrix and Vector Representation

In C# there are built in representations of 2D points and 2x2 matrices.
This is good enough for image processing, but I needed more than that for 3D graphics.

I wrote classes for:

• 3D vector
• 3x3 matrix
• 4x4 matrix
• Any size matrix

All the first three objects can be represented by "Any size matrix", but it is much more efficient to use the specific class you need.

Code:

class Vector3
{
    public static Vector3 Zero = NewZero();
    public static Vector3 One = NewOne();

    public float x;
    public float y;
    public float z;

    public Vector3()
    {
        x = 0.0f;
        y = 0.0f;
        z = 0.0f;
    }

    public Vector3(float x, float y, float z)
    {
        this.x = x;
        this.y = y;
        this.z = z;
    }

    public Vector3(float xyz)
    {
        this.x = xyz;
        this.y = xyz;
        this.z = xyz;
    }

    public Vector3(Vector3 v)
    {
        this.x = v.x;
        this.y = v.y;
        this.z = v.z;
    }

    public static Vector3 NewZero()
    {
        return new Vector3(0.0f);
    }

    public static Vector3 NewOne()
    {
        return new Vector3(1.0f);
    }

    public float DotProduct(Vector3 other)
    {
        return x * other.x + y * other.y + z * other.z;
    }

    public static Vector3 operator +(Vector3 v1, Vector3 v2)
    {
        return new Vector3(v1.x + v2.x, v1.y + v2.y, v1.z + v2.z);
    }

    public static Vector3 operator -(Vector3 v1, Vector3 v2)
    {
        return new Vector3(v1.x - v2.x, v1.y - v2.y, v1.z - v2.z);
    }

    public static Vector3 operator -(Vector3 v)
    {
        return new Vector3(-v.x, -v.y, -v.z);
    }

    public static Vector3 operator *(Vector3 v, float scalar)
    {
        return new Vector3(v.x * scalar, v.y * scalar, v.z * scalar);
    }

    public static Vector3 operator /(Vector3 v, float scalar)
    {
        return new Vector3(v.x / scalar, v.y / scalar, v.z / scalar);
    }

    public static bool operator ==(Vector3 v1, Vector3 v2)
    {
        return v1.x == v2.x && v1.y == v2.y && v1.z == v2.z;
    }

    public static bool operator !=(Vector3 v1, Vector3 v2)
    {
        return v1.x != v2.x || v1.y != v2.y || v1.z != v2.z;
    }

    public static Vector3 CrossProduct(Vector3 a, Vector3 b)
    {
        return new Vector3(a.y * b.z - a.z * b.y, a.z * b.x - a.x * b.z, a.x * b.y - a.y * b.x);
    }

    public Vector3 Add(Vector3 v)
    {
        x += v.x;
        y += v.y;
        z += v.z;
        return this;
    }

    public float DistanceTo(Vector3 v)
    {
        float dx = this.x - v.x;
        float dy = this.y - v.y;
        float dz = this.z - v.z;
        return (float)Math.Sqrt(dx * dx + dy * dy + dz * dz);
    }

    public float Size()
    {
        return DistanceTo(Vector3.Zero);
    }

    public Vector3 Normalize()
    {
        float size = Size();
        this.x /= size;
        this.y /= size;
        this.z /= size;
        return this;
    }

    public Vector3 Clone()
    {
        return new Vector3(this);
    }

    public override string ToString()
    {
        return "(" + x + ", " + y + ", " + z + ")";
    }
}

class Matrix
{
    public float[,] matrix;
    public int rows;
    public int cols;

    public Matrix(int rows, int cols)
    {
        this.matrix = new float[rows, cols];
        this.rows = rows;
        this.cols = cols;
    }

    public Matrix(float[,] matrix)
    {
        this.matrix = matrix;
        this.rows = matrix.GetLength(0);
        this.cols = matrix.GetLength(1);
    }

    protected static float[,] Multiply(Matrix matrix, float scalar)
    {
        int rows = matrix.rows;
        int cols = matrix.cols;
        float[,] m1 = matrix.matrix;
        float[,] m2 = new float[rows, cols];
        for (int i = 0; i < rows; ++i)
        {
            for (int j = 0; j < cols; ++j)
            {
                m2[i, j] = m1[i, j] * scalar;
            }
        }
        return m2;
    }

    protected static float[,] Multiply(Matrix matrix1, Matrix matrix2)
    {
        int m1rows = matrix1.rows;
        int m1cols = matrix1.cols;
        int m2rows = matrix2.rows;
        int m2cols = matrix2.cols;
        if (m1cols != m2rows)
        {
            throw new ArgumentException();
        }
        float[,] m1 = matrix1.matrix;
        float[,] m2 = matrix2.matrix;
        float[,] m3 = new float[m1rows, m2cols];
        for (int i = 0; i < m1rows; ++i)
        {
            for (int j = 0; j < m2cols; ++j)
            {
                float sum = 0;
                for (int it = 0; it < m1cols; ++it)
                {
                    sum += m1[i, it] * m2[it, j];
                }
                m3[i, j] = sum;
            }
        }
        return m3;
    }

    public static Matrix operator *(Matrix m, float scalar)
    {
        return new Matrix(Multiply(m, scalar));
    }

    public static Matrix operator *(Matrix m1, Matrix m2)
    {
        return new Matrix(Multiply(m1, m2));
    }

    public override string ToString()
    {
        string res = "";
        for (int i = 0; i < rows; ++i)
        {
            if (i > 0)
            {
                res += "|";
            }
            for (int j = 0; j < cols; ++j)
            {
                if (j > 0)
                {
                    res += ",";
                }
                res += matrix[i, j];
            }
        }
        return "(" + res + ")";
    }
}

class Matrix3 : Matrix
{
    public Matrix3()
        : base(3, 3)
    {
    }

    public Matrix3(float[,] matrix)
        : base(matrix)
    {
        if (rows != 3 || cols != 3)
        {
            throw new ArgumentException();
        }
    }

    public static Matrix3 I()
    {
        return new Matrix3(new float[,] { 
        { 1.0f, 0.0f, 0.0f }, 
        { 0.0f, 1.0f, 0.0f }, 
        { 0.0f, 0.0f, 1.0f } });
    }

    public static Vector3 operator *(Matrix3 matrix3, Vector3 v)
    {
        float[,] m = matrix3.matrix;
        return new Vector3(
            m[0, 0] * v.x + m[0, 1] * v.y + m[0, 2] * v.z,
            m[1, 0] * v.x + m[1, 1] * v.y + m[1, 2] * v.z,
            m[2, 0] * v.x + m[2, 1] * v.y + m[2, 2] * v.z);
    }

    public static Matrix3 operator *(Matrix3 mat1, Matrix3 mat2)
    {
        float[,] m1 = mat1.matrix;
        float[,] m2 = mat2.matrix;
        float[,] m3 = new float[3, 3];
        m3[0, 0] = m1[0, 0] * m2[0, 0] + m1[0, 1] * m2[1, 0] + m1[0, 2] * m2[2, 0];
        m3[0, 1] = m1[0, 0] * m2[0, 1] + m1[0, 1] * m2[1, 1] + m1[0, 2] * m2[2, 1];
        m3[0, 2] = m1[0, 0] * m2[0, 2] + m1[0, 1] * m2[1, 2] + m1[0, 2] * m2[2, 2];
        m3[1, 0] = m1[1, 0] * m2[0, 0] + m1[1, 1] * m2[1, 0] + m1[1, 2] * m2[2, 0];
        m3[1, 1] = m1[1, 0] * m2[0, 1] + m1[1, 1] * m2[1, 1] + m1[1, 2] * m2[2, 1];
        m3[1, 2] = m1[1, 0] * m2[0, 2] + m1[1, 1] * m2[1, 2] + m1[1, 2] * m2[2, 2];
        m3[2, 0] = m1[2, 0] * m2[0, 0] + m1[2, 1] * m2[1, 0] + m1[2, 2] * m2[2, 0];
        m3[2, 1] = m1[2, 0] * m2[0, 1] + m1[2, 1] * m2[1, 1] + m1[2, 2] * m2[2, 1];
        m3[2, 2] = m1[2, 0] * m2[0, 2] + m1[2, 1] * m2[1, 2] + m1[2, 2] * m2[2, 2];
        return new Matrix3(m3);
    }

    public static Matrix3 operator *(Matrix3 m, float scalar)
    {
        return new Matrix3(Multiply(m, scalar));
    }
}

class Matrix4 : Matrix
{
    public static Matrix4 I = NewI();

    public Matrix4()
        : base(4, 4)
    {
    }

    public Matrix4(float[,] matrix)
        : base(matrix)
    {
        if (rows != 4 || cols != 4)
        {
            throw new ArgumentException();
        }
    }

    public static Matrix4 NewI()
    {
        return new Matrix4(new float[,] { 
        { 1.0f, 0.0f, 0.0f, 0.0f }, 
        { 0.0f, 1.0f, 0.0f, 0.0f }, 
        { 0.0f, 0.0f, 1.0f, 0.0f },
        { 0.0f, 0.0f, 0.0f, 1.0f } });
    }

    public static Vector3 operator *(Matrix4 matrix4, Vector3 v)
    {
        float[,] m = matrix4.matrix;
        float w = m[3, 0] * v.x + m[3, 1] * v.y + m[3, 2] * v.z + m[3, 3];
        return new Vector3(
            (m[0, 0] * v.x + m[0, 1] * v.y + m[0, 2] * v.z + m[0, 3]) / w,
            (m[1, 0] * v.x + m[1, 1] * v.y + m[1, 2] * v.z + m[1, 3]) / w,
            (m[2, 0] * v.x + m[2, 1] * v.y + m[2, 2] * v.z + m[2, 3]) / w
            );
    }

    public static Matrix4 operator *(Matrix4 mat1, Matrix4 mat2)
    {
        float[,] m1 = mat1.matrix;
        float[,] m2 = mat2.matrix;
        float[,] m3 = new float[4, 4];
        m3[0, 0] = m1[0, 0] * m2[0, 0] + m1[0, 1] * m2[1, 0] + m1[0, 2] * m2[2, 0] + m1[0, 3] * m2[3, 0];
        m3[0, 1] = m1[0, 0] * m2[0, 1] + m1[0, 1] * m2[1, 1] + m1[0, 2] * m2[2, 1] + m1[0, 3] * m2[3, 1];
        m3[0, 2] = m1[0, 0] * m2[0, 2] + m1[0, 1] * m2[1, 2] + m1[0, 2] * m2[2, 2] + m1[0, 3] * m2[3, 2];
        m3[0, 3] = m1[0, 0] * m2[0, 3] + m1[0, 1] * m2[1, 3] + m1[0, 2] * m2[2, 3] + m1[0, 3] * m2[3, 3];
        m3[1, 0] = m1[1, 0] * m2[0, 0] + m1[1, 1] * m2[1, 0] + m1[1, 2] * m2[2, 0] + m1[1, 3] * m2[3, 0];
        m3[1, 1] = m1[1, 0] * m2[0, 1] + m1[1, 1] * m2[1, 1] + m1[1, 2] * m2[2, 1] + m1[1, 3] * m2[3, 1];
        m3[1, 2] = m1[1, 0] * m2[0, 2] + m1[1, 1] * m2[1, 2] + m1[1, 2] * m2[2, 2] + m1[1, 3] * m2[3, 2];
        m3[1, 3] = m1[1, 0] * m2[0, 3] + m1[1, 1] * m2[1, 3] + m1[1, 2] * m2[2, 3] + m1[1, 3] * m2[3, 3];
        m3[2, 0] = m1[2, 0] * m2[0, 0] + m1[2, 1] * m2[1, 0] + m1[2, 2] * m2[2, 0] + m1[2, 3] * m2[3, 0];
        m3[2, 1] = m1[2, 0] * m2[0, 1] + m1[2, 1] * m2[1, 1] + m1[2, 2] * m2[2, 1] + m1[2, 3] * m2[3, 1];
        m3[2, 2] = m1[2, 0] * m2[0, 2] + m1[2, 1] * m2[1, 2] + m1[2, 2] * m2[2, 2] + m1[2, 3] * m2[3, 2];
        m3[2, 3] = m1[2, 0] * m2[0, 3] + m1[2, 1] * m2[1, 3] + m1[2, 2] * m2[2, 3] + m1[2, 3] * m2[3, 3];
        m3[3, 0] = m1[3, 0] * m2[0, 0] + m1[3, 1] * m2[1, 0] + m1[3, 2] * m2[2, 0] + m1[3, 3] * m2[3, 0];
        m3[3, 1] = m1[3, 0] * m2[0, 1] + m1[3, 1] * m2[1, 1] + m1[3, 2] * m2[2, 1] + m1[3, 3] * m2[3, 1];
        m3[3, 2] = m1[3, 0] * m2[0, 2] + m1[3, 1] * m2[1, 2] + m1[3, 2] * m2[2, 2] + m1[3, 3] * m2[3, 2];
        m3[3, 3] = m1[3, 0] * m2[0, 3] + m1[3, 1] * m2[1, 3] + m1[3, 2] * m2[2, 3] + m1[3, 3] * m2[3, 3];
        return new Matrix4(m3);
    }

    public static Matrix4 operator *(Matrix4 m, float scalar)
    {
        return new Matrix4(Multiply(m, scalar));
    }
}

C#: Rotation Matrix

Rotation matrices are used in 3D graphics to rotate vectors.
I use homogeneous coordinates, so the matrices are 4x4. If you want 3x3, just remove the last column and last row.
I wrote several functions:

• Rotation around X axis
• Rotation around Y axis
• Rotation around Z axis
• Rotation around all axes
• Rotation around any given axis
• Rotation from normal vector to normal vector

Apparently the 5th function is enough, because for example "Rotation around X axis" can be replace by rotation around (1,0,0), and "Rotation around all axes" is merely the product of 3 matrices. BUT, one should use the specific function he or she needs, because it is more efficient.
For matrix operations you can use this post.

Code:

public static Matrix4 GetRotationMatrixX(double angle)
{
    if (angle == 0.0)
    {
        return Matrix4.I;
    }
    float sin = (float)Math.Sin(angle);
    float cos = (float)Math.Cos(angle);
    return new Matrix4(new float[4, 4] {
        { 1.0f, 0.0f, 0.0f, 0.0f }, 
        { 0.0f, cos, -sin, 0.0f }, 
        { 0.0f, sin, cos, 0.0f }, 
        { 0.0f, 0.0f, 0.0f, 1.0f } });
}

public static Matrix4 GetRotationMatrixY(double angle)
{
    if (angle == 0.0)
    {
        return Matrix4.I;
    }
    float sin = (float)Math.Sin(angle);
    float cos = (float)Math.Cos(angle);
    return new Matrix4(new float[4, 4] {
        { cos, 0.0f, sin, 0.0f }, 
        { 0.0f, 1.0f, 0.0f, 0.0f }, 
        { -sin, 0.0f, cos, 0.0f }, 
        { 0.0f, 0.0f, 0.0f, 1.0f } });
}

public static Matrix4 GetRotationMatrixZ(double angle)
{
    if (angle == 0.0)
    {
        return Matrix4.I;
    }
    float sin = (float)Math.Sin(angle);
    float cos = (float)Math.Cos(angle);
    return new Matrix4(new float[4, 4] {
        { cos, -sin, 0.0f, 0.0f }, 
        { sin, cos, 0.0f, 0.0f }, 
        { 0.0f, 0.0f, 1.0f, 0.0f }, 
        { 0.0f, 0.0f, 0.0f, 1.0f } });
}

public static Matrix4 GetRotationMatrix(double ax, double ay, double az)
{
    Matrix4 my = null;
    Matrix4 mz = null;
    Matrix4 result = null;
    if (ax != 0.0)
    {
        result = GetRotationMatrixX(ax);
    }
    if (ay != 0.0)
    {
        my = GetRotationMatrixY(ay);
    }
    if (az != 0.0)
    {
        mz = GetRotationMatrixZ(az);
    }
    if (my != null)
    {
        if (result != null)
        {
            result *= my;
        }
        else
        {
            result = my;
        }
    }
    if (mz != null)
    {
        if (result != null)
        {
            result *= mz;
        }
        else
        {
            result = mz;
        }
    }
    if (result != null)
    {
        return result;
    }
    else
    {
        return Matrix4.I;
    }
}

public static Matrix4 GetRotationMatrix(Vector3 axis, double angle)
{
    if (angle == 0.0)
    {
        return Matrix4.I;
    }

    float x = axis.x;
    float y = axis.y;
    float z = axis.z;
    float sin = (float)Math.Sin(angle);
    float cos = (float)Math.Cos(angle);
    float xx = x * x;
    float yy = y * y;
    float zz = z * z;
    float xy = x * y;
    float xz = x * z;
    float yz = y * z;

    float[,] matrix = new float[4, 4];

    matrix[0, 0] = xx + (1 - xx) * cos;
    matrix[1, 0] = xy * (1 - cos) + z * sin;
    matrix[2, 0] = xz * (1 - cos) - y * sin;
    matrix[3, 0] = 0.0f;

    matrix[0, 1] = xy * (1 - cos) - z * sin;
    matrix[1, 1] = yy + (1 - yy) * cos;
    matrix[2, 1] = yz * (1 - cos) + x * sin;
    matrix[3, 1] = 0.0f;

    matrix[0, 2] = xz * (1 - cos) + y * sin;
    matrix[1, 2] = yz * (1 - cos) - x * sin;
    matrix[2, 2] = zz + (1 - zz) * cos;
    matrix[3, 2] = 0.0f;

    matrix[3, 0] = 0.0f;
    matrix[3, 1] = 0.0f;
    matrix[3, 2] = 0.0f;
    matrix[3, 3] = 1.0f;

    return new Matrix4(matrix);
}

/// <param name="source">Should be normalized</param>
/// <param name="destination">Should be normalized</param>
public static Matrix4 GetRotationMatrix(Vector3 source, Vector3 destination)
{
    Vector3 rotaxis = Vector3.CrossProduct(source, destination);
    if (rotaxis != Vector3.Zero)
    {
        rotaxis.Normalize();
        float cos = source.DotProduct(destination);
        double angle = Math.Acos(cos);
        return GetRotationMatrix(rotaxis, angle);
    }
    else
    {
        return Matrix4.I;
    }
}

How to connect to a remote computer with a click (VNC Step By Step)

What:

Why:
A few years ago I sent some files to a client by email, and I spent 3 hours over the phone trying to explain to him how to copy those files to C:\Program Files. Eventually I gave up. It would be faster for me to drive all the way to his office, do it myself, and return all the way. That's exactly what I did, but I also installed a secured VNC server so next time I won't have to drive.
After that I began to install a VNC server everywhere - my grandma who always asks for help, the media center in the living room, a virtual machine, my remote server, ...
I use it very often so it must be comfortable to use.

How:
There are a few things to do: installation, opening ports, configuring dns, creating vnc file

1. Download VNC
You can get the free edition from here: http://www.realvnc.com
Please note that this version has no encryption (it has a password though), so if security is really important you should get the full version.

2. Install
Install the VNC Viewer on your computer, and the VNC Server on the remote computer.
In the end of the Server installation, set a password:

3. Open port 5900 on the Server side
Most people have routers that block incoming connections. You need to open port 5900 on the Server side (TCP if you were wondering).
First, let's be smart and check whether it's already opened: http://www.yougetsignal.com/tools/open-ports/
If the port is blocked, you may need to access your router and open it. This site has detailed explanation for doing this for every router in the world: http://portforward.com/
Note: If you are not allowed or can't open ports on the Server side then you can use the "Listening mode" viewer, but then the rest of this post doesn't help you.


4. Test it
On the Server side find the IP address: http://www.whatismyip.com/
On the Client side open VNC Viewer, enter the Server's IP address, and click OK:

You will be asked for a password. You should enter the password from Step 2 above.
If everything went OK you should now see the Server's desktop inside a window on the Client side. If you get an error message, try googling it.

5. Create DNS
Why? Because usually the Server's IP address can change. If it's static you can skip to Step 8.
Go to: http://www.dyndns.com/ and create a new account.
Add a new host; don't mind the IP for now:

6. Update DNS
Download and install DynDNS Updater on the Server side.
During the installation I advise on DISABLING "Internet Guide":

You will be asked for your account's username and password. Then select the host you added earlier and click OK:

Note: Some routers have this feature built in. I know some of the D-Links have it for example. Use can use it instead of the DynDNS Updater, but you should do it only if you know what you are doing. Example of this feature on my D-Link router:

7. Test it
On the Client side open VNC Viewer, enter the host address, and click OK:

Again, if you are asked for the password, enter it (the one from Step 2). You should get a window with the Server's desktop. Don't close it, we need it for the next step.

8. Save Connection
If you didn't connect to the Server do it now. Right-click the top of the window and click on "options":

In the new window click the "Load / Save" tab and then "Save As...":

Choose a location (e.g. your Desktop) and a name (e.g. "My Remote Server") and save it. You will probably get the following screen:

It's your choice whether to click Yes or No.
If you click No you will have to type in the password each time you want to connect.
If you click Yes, then everything is automatic (no need to type password). Well, the message is pretty accurate: "it's more convenient, but...".
Explanation: If you click yes you will have automatic access to the remote computer. So if someone gains access to your computer, then he will have access to the remote computer as well.
My advice is to click Yes for your Media Center, local server or grandma, but to click No for business computer or something important.

9. That's it!
Go to the location of the file you saved earlier and open it: