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OpenSSL bug or why some private keys cannot be used for .NET

More than half year ago, I wrote an article about importing RSA private key in PEM format into C# RSACryptoProvider. This code was used by me for a long time until two days ago I got private key which I was unable to import due to “Bad Data” CryptographicException. And here the story begins…

Bug crime

First thing to do in such cases is to check who’s bug is it. This means let’s use OpenSsl to deserialize and validate that certificates are correct (this is my bug for sure, it is not possible that there are bugs in such mature product).

> openssl x509 -noout -modulus -in cert.pem | openssl md5
(stdin)= d1eda6b5f39cd………43d50ee2c4e08

> openssl rsa -noout -modulus -in key.pem | openssl md5
Enter pass phrase for key.pem:
(stdin)= d1eda6b5f39cd………43d50ee2c4e08

Looks perfectly right. So it’s clearly my problem… and I entered into heavy debugging PEM parser. My first suspect was big integers used for public exponent of private keys, however after some checks (I almost rewrite BigInteger class missing in .NET 3.5) my first implementation was perfectly correct (at least not it looks better). Second victim became high bit of integers used for both primes. But after short check it also looks ok.

Then my accusing finger was pointed to ASN.1 DER parser. More precisely, into my implementation of length octets. As you remember, we are checking “hardcoded” for high bit in first octet and then just read low bits of following octet into swapped array. Then removing all trailing zeros and subtract it from the actual length.This is what is used to be:

private static Func<BinaryReader, int> _getIntSize = r => {
   byte lb = 0×00;
   byte hb = 0×00;
   int c = 0;
   var b = r.ReadByte();
   if (b != 0×02) { //int
      return 0;
   }
   b = r.ReadByte();

   if (b == 0×81) {
      c = r.ReadByte(); //size
   } else
      if (b == 0×82) {
         hb = r.ReadByte(); //size
         lb = r.ReadByte();
         byte[] m = { lb, hb, 0×00, 0×00 };
         c = BitConverter.ToInt32(m, 0);
      } else {
         c = b; //got size
      }

   while (r.ReadByte() == 0×00) { //remove high zero
      c -= 1;
   }
   r.BaseStream.Seek(-1, SeekOrigin.Current); // last byte is not zero, go back;
   return c;
};

Code looks not very clean and too specific for such action. You, probably, familiar with this feeling of “oh my god, what I though about when I wrote it a year ago?”. So I decided to rewrite it.

According ISO 8825-1:2003  In the long form, the length octets shall consist of an initial octet and one or more subsequent octets. The initial octet shall be encoded as follows:
a) bit 8 shall be one;
b) bits 7 to 1 shall encode the number of subsequent octets in the length octets, as an unsigned binary integer
with bit 7 as the most significant bit;
c) the value 111111112 shall not be used.

Let’s do it

if ((b & 0×80) == 0×80) { //check whether long form
  var l = b & ~0×80;
  var d = r.ReadBytes(l);
  var dl = new byte[4];
  d.CopyTo(dl, 0);
  c = BitConverter.ToInt32(dl, 0);
}

Now it looks much nicer and correct. For short form nothing changed as well as for trailing zeros. Also the problem remains.

But wait, trailing zeros. Maybe the problem there? The only reason to have zero octets is indefinite length. In this case we should find single octet (one with last bit set only) at the beginning and two zero octets at the end. So in any case of having definite length of type one or two we can safely remove trailing zeros and subtract length or not remove it, the result will be the same since we are using the same endian. So what is the problem? Let’s open hex editor and compare “good” and “bad” keys.

image

Nothing special can be found in those two keys. Both looks ok, but, wait… How is it possible that exponent2 is smaller than exponent1 and coefficient?

image

Maybe it is because of trailing spaces? Let’s trim it.

image

As you can clearly see, in bad sample length of exponent2 is not equal to primes and other exponents. This is the reason why we were not able to read and use it. But how it works in OpenSSL? Let’s look into ASN1_INTEGER object. According DER spec, when we are encoding in long form, bit 8 will be set to 1, this means that inside ASN1_INTEGER if it starts from byte larger then 0×80 additional zero pad should be added. However when encoding negative integers, trailing zero will become 0xFF+additional zero at the end due to carry. In this case, OpenSSL serializer should add as many trailing zeros as it required by source number (prime or modulus in this case). This is what OpenSSL not doing.

In other case if the first byte is greater than 0×80 we should pad 0xFF, however if first byte is 0×80 and one of the following bytes is non-zero we should pad 0xFF to distinct 0×80 (which is indefinite length, remember?). Also if it followed by additional zeros it should not be padded.

The bad news, that all this is voided in all version of OpenSSL with win comments like “we have now cleared all the crap”, “a miss or crap from the other end” or “We’ve already written n zeros so we just append an extra one and set the first byte to a 1.”.

The good news, that nobody cares because this part is complicated and usually encoded and decoded by the same library. The only problem is when there are two implementations are in use: OpenSSL one and other which is strictly enforces the ISO 8825 . Just like in our case.

To workaround the problem we can add custom logic to add trailing zeros at the beginning of each integer when we know the target size, based of source.

var MODULUS = _readInt(reader); // assuming that modulus is correct
var E = _readInt(reader);
var D = _normalize(_readInt(reader), MODULUS.Length); // private exponent
var P = _normalize(_readInt(reader), MODULUS.Length / 2); // prime 1
var Q = _normalize(_readInt(reader), MODULUS.Length / 2); ; // prime 2
var DP = _normalize(_readInt(reader), P.Length);
var DQ = _normalize(_readInt(reader), Q.Length);
var IQ = _normalize(_readInt(reader), Q.Length);

private static byte[] _normalize(byte[] trg, int len) {
   byte[] r;
   if (len > trg.Length) {
      r = new byte[len];
      trg.CopyTo(r, len – trg.Length);
   } else {
      r = trg;
   }
   return r;
}

Or, better idea is to fix it in OpenSSL, but, probably, this will break thousands of applications, so it is almost sure that such fix will rest in peace inside dev branch for a long long time.

Be good people and do not follow specifications to win extra days of your life.

Real singleton approach in WPF application

One of the most common problems in WPF is memory/processor time consumption. Yes, WPF is rather greedy framework. It become even greedier when using unmanaged resources, such as memory files or interop images. To take care on it, you can implement singleton pattern for the application and share only one unmanaged instance among different application resources. So today we’ll try to create one large in-memory dynamic bitmap and share it between different instances of WPF controls. Let’s start

The Singleton

First of all let’s create our single instance source. The pattern is straight forward. Create a class derived from INotifyPropertyChanged, create private constructor and static member returns the single instance of the class.

public class MySingleton : INotifyPropertyChanged {

   #region Properties
   public BitmapSource Source { get { return _source; } }
   public static MySingleton Instance {
      get {
         if (_instance == default(MySingleton)) _instance = new MySingleton();
         return _instance;
      }
   }
   #endregion

   #region ctor
   private MySingleton() { _init(); }
   #endregion

Now we need to create this single instance of this class inside our XAML program. To do this, we have great extension x:Static

<Window.DataContext>
    <x:StaticExtension Member="l:MySingleton.Instance" />
</Window.DataContext>

Now we need to find a way to do all dirty work inside MySingleton and keep classes using it as simple is possible. For this purpose we’ll register class handler to catch all GotFocus routed events, check the target of the event and rebind the only instance to new focused element. How to do this? Simple as 1-2-3

Create class handler

EventManager.RegisterClassHandler(typeof(FrameworkElement), FrameworkElement.GotFocusEvent, (RoutedEventHandler)_onAnotherItemFocused);

Check whether selected and focused item of the right type

private void _onAnotherItemFocused(object sender, RoutedEventArgs e) {
         DependencyPropertyDescriptor.FromProperty(ListBoxItem.IsSelectedProperty, typeof(ListBoxItem)).AddValueChanged(sender, (s, ex) => {}

and reset binding

var item = s as ListBoxItem;
var img = item.Content as Image;
if (_current != null && _current.Target is Image && _current.Target != img) {
   ((Image)_current.Target).ClearValue(Image.SourceProperty);
}
if (img != null) {
   _current = new WeakReference(img);
   img.SetBinding(Image.SourceProperty, _binding);
}

We almost done. a bit grease to make the source bitmap shiny

var count = (uint)(_w * _h * 4);
var section = CreateFileMapping(new IntPtr(-1), IntPtr.Zero, 0×04, 0, count, null);
_map = MapViewOfFile(section, 0xF001F, 0, 0, count);
_source = Imaging.CreateBitmapSourceFromMemorySection(section, _w, _h, PixelFormats.Bgr32, (int)(_w * 4), 0) as InteropBitmap;
_binding = new Binding {
   Mode = BindingMode.OneWay,
   Source = _source
};
CompositionTarget.Rendering += (s, e) => { _invalidate(); };

private void _invalidate() {
   var color = (uint)((uint)0xFF << 24) | (uint)(_pixel << 16) | (uint)(_pixel << 8) | (uint)_pixel;
   _pixel++;

   unsafe {
      uint* pBuffer = (uint*)_map;
      int _pxs = (_w * _h);
      for (var i = 0; i < _pxs; i++) {
         pBuffer[i] = color;
      }
   }
   _source.Invalidate();
   OnPropertyChanged("Source");
}

And we done. The usage of this approach is very simple – there is no usage at all. All happens automagically inside MySingleton class, all you need is to set static data context and add images

<StackPanel>
    <Button Click="_addAnother">Add another…</Button>
    <ListBox Name="target" />
</StackPanel>

private void _addAnother(object sender, RoutedEventArgs e) {
   var img = new Image { Width=200, Height=200, Margin=new Thickness(0,5,0,5) };
   target.Items.Add(img);
   this.Height += 200;
}

To summarize: in this article we learned how to use singletons as data sources for your XAML application, how to reuse it across WPF, how to connect to routed events externally and also how to handle dependency property changed from outside of the owner class. Have a nice day and be good people.

Source code for this article (21k) >>

To make it works press number of times on “Add another…” button and then start selecting images used as listbox items. Pay attention to the working set of the application. Due to the fact that only one instance is in use it is not growing.

INotifyPropertyChanged auto wiring or how to get rid of redundant code

For the last week most of WPF disciples are discussing how to get rid of hardcoded property name string inside INotifyPropertyChanged implementation and how to keep using automatic properties implementation but keep WPF binding working. The thread was started by Karl Shifflett, who proposed interesting method of using StackFrame for this task. During this thread other methods were proposed including code snippets, R#, Observer Pattern, Cinch framework, Static Reflection, Weak References and others. I also proposed the method we’re using for our classes and promised to blog about it. So the topic today is how to use PostSharp to wire automatic implementation of INotifyPropertyChanged interface based on automatic setters only.

My 5 ¢

So, I want my code to looks like this:

public class AutoWiredSource {
   public double MyProperty { get; set; }
   public double MyOtherProperty { get; set; }
}

while be fully noticeable about any change in any property and makes me able to bind to those properties.

<StackPanel DataContext="{Binding Source={StaticResource source}}">
    <Slider Value="{Binding Path=MyProperty}" />
    <Slider Value="{Binding Path=MyProperty}" />
</StackPanel>

How to achieve it? How to make compiler to replace my code with following?:

private double _MyProperty;
public double MyProperty {
   get { return _MyProperty; }
   set {
      if (value != _MyProperty) {
         _MyProperty = value; OnPropertyChanged("MyProperty");
      }
   }
}
public event PropertyChangedEventHandler PropertyChanged;
internal void OnPropertyChanged(string propertyName) {
   if (string.IsNullOrEmpty(propertyName)) throw new ArgumentNullException("propertyName");

   var handler = PropertyChanged as PropertyChangedEventHandler;
   if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}

Simple: to use aspect oriented programming to inject set of instructions into pre-compiled source.

First of all we have to build some attribute will be used for marking classes requires change tracking. This attribute should be combined (compound) aspect to include all aspects used for change tracking. All we’re doing here is to get all set methods to add composition aspect to

[Serializable, DebuggerNonUserCode, AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class, AllowMultiple = false, Inherited = false),
MulticastAttributeUsage(MulticastTargets.Class, AllowMultiple = false, Inheritance = MulticastInheritance.None, AllowExternalAssemblies = true)]
public sealed class NotifyPropertyChangedAttribute : CompoundAspect {
   public int AspectPriority { get; set; }

   public override void ProvideAspects(object element, LaosReflectionAspectCollection collection) {
      Type targetType = (Type)element;
      collection.AddAspect(targetType, new PropertyChangedAspect { AspectPriority = AspectPriority });
      foreach (var info in targetType.GetProperties(BindingFlags.Public | BindingFlags.Instance).Where(pi => pi.GetSetMethod() != null)) {
         collection.AddAspect(info.GetSetMethod(), new NotifyPropertyChangedAspect(info.Name) { AspectPriority = AspectPriority });
      }
   }
}

Next aspect is change tracking composition aspect. Which is used for marking only

[Serializable]
internal sealed class PropertyChangedAspect : CompositionAspect {
   public override object CreateImplementationObject(InstanceBoundLaosEventArgs eventArgs) {
      return new PropertyChangedImpl(eventArgs.Instance);
   }

   public override Type GetPublicInterface(Type containerType) {
      return typeof(INotifyPropertyChanged);
   }

   public override CompositionAspectOptions GetOptions() {
      return CompositionAspectOptions.GenerateImplementationAccessor;
   }
}

And the next which is most interesting one, we will put onto method boundary for tracking. There are some highlights here. First we do not want to fire PropertyChanged event if the actual value did not changed, thus we’ll handle the method on it entry and on it exit for check.

[Serializable]
internal sealed class NotifyPropertyChangedAspect : OnMethodBoundaryAspect {
   private readonly string _propertyName;

   public NotifyPropertyChangedAspect(string propertyName) {
      if (string.IsNullOrEmpty(propertyName)) throw new ArgumentNullException("propertyName");
      _propertyName = propertyName;
   }

   public override void OnEntry(MethodExecutionEventArgs eventArgs) {
      var targetType = eventArgs.Instance.GetType();
      var setSetMethod = targetType.GetProperty(_propertyName);
      if (setSetMethod == null) throw new AccessViolationException();
      var oldValue = setSetMethod.GetValue(eventArgs.Instance,null);
      var newValue = eventArgs.GetReadOnlyArgumentArray()[0];
      if (oldValue == newValue) eventArgs.FlowBehavior = FlowBehavior.Return;
   }

   public override void OnSuccess(MethodExecutionEventArgs eventArgs) {
      var instance = eventArgs.Instance as IComposed<INotifyPropertyChanged>;
      var imp = instance.GetImplementation(eventArgs.InstanceCredentials) as PropertyChangedImpl;
      imp.OnPropertyChanged(_propertyName);
   }
}

We almost done, all we have to do is to create class which implements INotifyPropertyChanged with internal method to useful call

[Serializable]
internal sealed class PropertyChangedImpl : INotifyPropertyChanged {
   private readonly object _instance;

   public PropertyChangedImpl(object instance) {
      if (instance == null) throw new ArgumentNullException("instance");
      _instance = instance;
   }

   public event PropertyChangedEventHandler PropertyChanged;

   internal void OnPropertyChanged(string propertyName) {
      if (string.IsNullOrEmpty(propertyName)) throw new ArgumentNullException("propertyName");

      var handler = PropertyChanged as PropertyChangedEventHandler;
      if (handler != null) handler(_instance, new PropertyChangedEventArgs(propertyName));
   }
}

We done. The last thing is to reference to PostSharp Laos and Public assemblies and mark compiler to use Postsharp targets (inside your project file (*.csproj)

<Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
<PropertyGroup>
  <DontImportPostSharp>True</DontImportPostSharp>
</PropertyGroup>
<Import Project="PostSharp\PostSharp-1.5.targets" />

Now we done. We can use clear syntax like following to make all our properties has public setter to be traceable. The only disadvantage is that you’ll have to drag two Post Sharp files with your project. But after all it much more convenience than manual notify change tracking all over your project.

[NotifyPropertyChanged]
public class AutoWiredSource {
   public double MyProperty { get; set; }
}

Have a nice day and be good people. Also try to thing what other extremely useful things can be done with PostSharp (or any other aspect oriented engine)

Source code for this article (1,225 KB)>>

“Zone of Pain vs. Zone of Uselessness” or code analysis with NDepend

As for me, there are only two kinds of projects – hobbyist’s nifty tools and systems (scale may wary). The main difference between those is the easiness of making changes and refactoring. Other words, how many other developers I should persuade to do it just because “In the final analysis, it’s their war” – JFK. But what can be the good reason for such fast talk? – “You code sucks or at least it ought to”.

AbstractnessVSInstabilityAbstractnessVSInstability[10]
“Every generation needs a new revolution” – Thomas Jefferson

So, in order to win such revolution for “systems” you absolutely need static analysis tools like NDepend. Those tools are not intended for being your advocates, but those intended to help you to understand all risks and approximate the amount of work should be done to fulfill another revolution.

Unfortunately, you cannot use such tools for fair measuring of code quality because of Computer Science rules of thumb. How to decide whether “methods is too big” or “method is too complex”? However you can (and should) use it for dependencies risk detection. For example, in following illustration you can clear understand that any change inside BetterPlace.Core or BetterPlace.Model assemblies (and namespaces) can be painful.

Dependencies diagram

Now the only question is who is responsible of modules, using it and how long will it take to convince them to make a revolution.

 Dependency Matrix

From here you can start using CQL (Code Query Language) which is SQL like language invented by Patrick, the author of NDepend, for querying code elements and sections. By using it, you can define what “method is too big” means in terms of your project.

SELECT METHODS WHERE NbLinesOfCode > 300 ORDER BY NbLinesOfCode DESC

Or see where you should replace method overloads by default arguments, introduced in .NET 4.0

SELECT METHODS WHERE NbOverloads > 1 ORDER BY NbOverloads DESC

Then, when you marked all places and human targets for revolution, you can start it. After you done, you can even compare builds and measure the amount of work and quality of results achieved.

Application metrix Application metrix

To finalize, I just touched the tip of what good static analysis tool can be used for. So get it, learn it and use it not only when you need to make a revolutions, but also during your application design and build process to be aware about how the new monster created will looks like.

Download NDepend >>

Proper disclosure: Apr 15, Patrick, the author of NDepend, asked me to review his tool and offer one license for evaluation. I told him, that do not need to evaluate it because I’m using it for a while (also I had the license of my own) and I’ll be happy to write a review once I’ll have a bit time for it. Now it happened. Thank you, Patrick, for such good work!

How to calculate CRC in C#?

First of all, I want to beg your pardon about the frequency of posts last time. I’m completely understaffed and have a ton of things to do for my job. This why, today I’ll just write a quick post about checksum calculation in C#. It might be very useful for any of you, working with devices or external systems.

BIOS CRC Error for old thinkpad

CRC – Cyclic Redundancy Check is an algorithm, which is widely used in different communication protocols, packing and packaging algorithms for assure robustness of data. The idea behind it is simple – calculate unique checksum (frame check sequence) for each data frame, based on it’s content and stick it at the end of each meaningful message. Once data received it’s possible to perform the same calculating and compare results – if results are similar, message is ok.

There are two kinds of CRC – 16 and 32 bit. There are also less used checksums for 8 and 64 bits. All this is about appending a string of zeros to the frame equal in number of frames and modulo two device by using generator polynomial containing one or more bits then checksum to be generated. This is very similar to performing a bit-wise XOR operation in the frame, while the reminder is actually our CRC.

In many industries first polynomial is in use to create CRC tables and then apply it for performance purposes. The default polynomial, defined by IEEE 802.3 which is 0xA001 for 16 bit and 0x04C11DB7 for 32 bit. We’re in C#, thus we should use it inversed version which is 0×8408 for 16 bit and 0xEDB88320 for 32 bit. Those polynomials we’re going to use also in our sample.

So let’s start. Because CRC is HashAlgorithm after all, we can derive our classes from System.Security.Cryptography.HashAlgorithm class.

public class CRC16 : HashAlgorithm {
public class CRC32 : HashAlgorithm {

Then, upon first creation we’ll generate hashtables with CRC values to enhance future performance. It’s all about values table for bytes from 0 to 255 , so we should calculate it only once and then we can use it statically.

[CLSCompliant(false)]
public CRC16(ushort polynomial) {
HashSizeValue = 16;
_crc16Table = (ushort[])_crc16TablesCache[polynomial];
if (_crc16Table == null) {
_crc16Table = CRC16._buildCRC16Table(polynomial);
_crc16TablesCache.Add(polynomial, _crc16Table);
}
Initialize();
}

[CLSCompliant(false)]
public CRC32(uint polynomial) {
HashSizeValue = 32;
_crc32Table = (uint[])_crc32TablesCache[polynomial];
if (_crc32Table == null) {
_crc32Table = CRC32._buildCRC32Table(polynomial);
_crc32TablesCache.Add(polynomial, _crc32Table);
}
Initialize();
}

Then let’s calculate it

private static ushort[] _buildCRC16Table(ushort polynomial) {
// 256 values representing ASCII character codes.
ushort[] table = new ushort[256];
for (ushort i = 0; i < table.Length; i++) {
ushort value = 0;
ushort temp = i;
for (byte j = 0; j < 8; j++) {
if (((value ^ temp) & 0×0001) != 0) {
value = (ushort)((value >> 1) ^ polynomial);
} else {
value >>= 1;
}
temp >>= 1;
}
table[i] = value;
}
return table;
}

private static uint[] _buildCRC32Table(uint polynomial) {
uint crc;
uint[] table = new uint[256];

// 256 values representing ASCII character codes.
for (int i = 0; i < 256; i++) {
crc = (uint)i;
for (int j = 8; j > 0; j–) {
if ((crc & 1) == 1)
crc = (crc >> 1) ^ polynomial;
else
crc >>= 1;
}
table[i] = crc;
}

return table;
}

The result will looks like this for 32 bits

        0x00, 0x31, 0x62, 0x53, 0xC4, 0xF5, 0xA6, 0x97,
        0xB9, 0x88, 0xDB, 0xEA, 0x7D, 0x4C, 0x1F, 0x2E,
        0x43, 0x72, 0x21, 0x10, 0x87, 0xB6, 0xE5, 0xD4,
        0xFA, 0xCB, 0x98, 0xA9, 0x3E, 0x0F, 0x5C, 0x6D,
        0x86, 0xB7, 0xE4, 0xD5, 0x42, 0x73, 0x20, 0x11,
        0x3F, 0x0E, 0x5D, 0x6C, 0xFB, 0xCA, 0x99, 0xA8,
        0xC5, 0xF4, 0xA7, 0x96, 0x01, 0x30, 0x63, 0x52,
        0x7C, 0x4D, 0x1E, 0x2F, 0xB8, 0x89, 0xDA, 0xEB,
        0x3D, 0x0C, 0x5F, 0x6E, 0xF9, 0xC8, 0x9B, 0xAA,
        0x84, 0xB5, 0xE6, 0xD7, 0x40, 0x71, 0x22, 0x13,
        0x7E, 0x4F, 0x1C, 0x2D, 0xBA, 0x8B, 0xD8, 0xE9,
        0xC7, 0xF6, 0xA5, 0x94, 0x03, 0x32, 0x61, 0x50,
        0xBB, 0x8A, 0xD9, 0xE8, 0x7F, 0x4E, 0x1D, 0x2C,
        0x02, 0x33, 0x60, 0x51, 0xC6, 0xF7, 0xA4, 0x95,
        0xF8, 0xC9, 0x9A, 0xAB, 0x3C, 0x0D, 0x5E, 0x6F,
        0x41, 0x70, 0x23, 0x12, 0x85, 0xB4, 0xE7, 0xD6,
        0x7A, 0x4B, 0x18, 0x29, 0xBE, 0x8F, 0xDC, 0xED,
        0xC3, 0xF2, 0xA1, 0x90, 0x07, 0x36, 0x65, 0x54,
        0x39, 0x08, 0x5B, 0x6A, 0xFD, 0xCC, 0x9F, 0xAE,
        0x80, 0xB1, 0xE2, 0xD3, 0x44, 0x75, 0x26, 0x17,
        0xFC, 0xCD, 0x9E, 0xAF, 0x38, 0x09, 0x5A, 0x6B,
        0x45, 0x74, 0x27, 0x16, 0x81, 0xB0, 0xE3, 0xD2,
        0xBF, 0x8E, 0xDD, 0xEC, 0x7B, 0x4A, 0x19, 0x28,
        0x06, 0x37, 0x64, 0x55, 0xC2, 0xF3, 0xA0, 0x91,
        0x47, 0x76, 0x25, 0x14, 0x83, 0xB2, 0xE1, 0xD0,
        0xFE, 0xCF, 0x9C, 0xAD, 0x3A, 0x0B, 0x58, 0x69,
        0x04, 0x35, 0x66, 0x57, 0xC0, 0xF1, 0xA2, 0x93,
        0xBD, 0x8C, 0xDF, 0xEE, 0x79, 0x48, 0x1B, 0x2A,
        0xC1, 0xF0, 0xA3, 0x92, 0x05, 0x34, 0x67, 0x56,
        0x78, 0x49, 0x1A, 0x2B, 0xBC, 0x8D, 0xDE, 0xEF,
        0x82, 0xB3, 0xE0, 0xD1, 0x46, 0x77, 0x24, 0x15,
        0x3B, 0x0A, 0x59, 0x68, 0xFF, 0xCE, 0x9D, 0xAC

Now, all we have to do is to upon request to lookup into this hash table for related value and XOR it

protected override void HashCore(byte[] buffer, int offset, int count) {

for (int i = offset; i < count; i++) {

ulong ptr = (_crc & 0xFF) ^ buffer[i];

_crc >>= 8;

_crc ^= _crc32Table[ptr];

}

}

new public byte[] ComputeHash(Stream inputStream) {

byte[] buffer = new byte[4096];

int bytesRead;

while ((bytesRead = inputStream.Read(buffer, 0, 4096)) > 0) {

HashCore(buffer, 0, bytesRead);

}

return HashFinal();

}

protected override byte[] HashFinal() {

byte[] finalHash = new byte[4];

ulong finalCRC = _crc ^ _allOnes;

finalHash[0] = (byte)((finalCRC >> 0) & 0xFF);

finalHash[1] = (byte)((finalCRC >> 8) & 0xFF);

finalHash[2] = (byte)((finalCRC >> 16) & 0xFF);

finalHash[3] = (byte)((finalCRC >> 24) & 0xFF);

return finalHash;

}

We done. Have a good time and be good people. Also, I want to thank Boris for helping me with this article. He promised to write here some day…

Source code for this article

Some new in-mix downloads

There are some very cool downloads suddenly appear on MSDN download site due to all new technologies, presented at Mix ‘09. So let’s start

To learn more about Silverlight 3.0 and Blend 3.0, you can see first day keynotes at mix 09, Rollup of what’s new in Silverlight 3 by Joe Stegman. This includes offline mode support by Mike Harsh. I’ll write another separate post for this topic, due to the fact, that I’m a desktop guy, so wary about the future of WPF.

To learn more about how to use new Expression Blend, it worth to see this session by Pete Blois. Another good sessions are also wrapped for you by Scott Hanselman.

After we done with all web stuff, let’s speak about a client

That’s all by now, going to write a review for new book and will publish it soon (probably even before, you’ll finish with all those downloads and readings). So, stay tuned and be good people.

WPF Line-Of-Business labs and Silverlight vs. Flash

Small update today (mostly interesting links)… During my last “Smart Client” session I was asked about WPF LOB application development labs. So, there are two full labs, I noticed about:

Both labs include WPF ribbon and DataGrid, Southridge also come with M-VV-M design sample and some other interesting features. As for me, it seemed, like some parts of those labs can be easily used “as-is” for production level applications, like it was done with SCE starter, which turned into TimesReader (by the way, it has free version again).

Line of Business Hands-On-Lab Material

For those, who still trying to consider what to use for their next killer app, I propose to read following article from Jordan, which compares between Silverlight and Flash. And then see composite application guidance to use Prism for Silverlight development. Here the video of it usage by Adam Kinney from Channel 9

Prism for Silverlight

Have a nice day and be good people

Slides and desks from Smart Client Development session

Great thank to everybody attended yesterday at “Smart Client development” session. As promises, please see slides and desks from this session

Quick how to: Reduce number of colors programmatically

My colleague just asked me about how to reduce a number of colors in image programmatically. This is very simple task and contains of 43 :) steps:

Simple color matrix

First of all, you have to read a source image

using (var img = Image.FromFile(name)) {
var bmpEncoder = ImageCodecInfo.GetImageDecoders().FirstOrDefault(e => e.FormatID == ImageFormat.Bmp.Guid);

Then create your own encoder with certain color depth (32 bits in this case)

var myEncoder = System.Drawing.Imaging.Encoder.ColorDepth;
var myEncoderParameter = new EncoderParameter(myEncoder, 32L);
var myEncoderParameters = new EncoderParameters(1) { Param = new EncoderParameter[] { myEncoderParameter } };

Then save it

img.Save(name.Replace(“.png”, “.bmp”), bmpEncoder, myEncoderParameters);

It it enough? Not really, because if you’re going to loose colors (by reducing color depth), it makes sense to avoid letting default WIX decoder to do this, thus you have to find nearest base colors manually. How to do this? By using simple math

Color GetNearestBaseColor(Color exactColor) {
Color nearestColor = Colors.Black;
int cnt = baseColors.Count;
for (int i = 0; i < cnt; i++) {
int rRed = baseColors[i].R – exactColor.R;
int rGreen = baseColors[i].G – exactColor.G;
int rBlue = baseColors[i].B – exactColor.B;

int rDistance =
(rRed * rRed) +
(rGreen * rGreen) +
(rBlue * rBlue);
if (rDistance == 0.0) {
return baseColors[i];
} else if (rDistance < maxDistance) {
maxDistance = rDistance;
nearestColor = baseColors[i];
}
}
return nearestColor;
}

Now, you can either change colors on base image directly

unsafe {
uint* pBuffer = (uint*)hMap;
for (int iy = 0; iy < (int)ColorMapSource.PixelHeight; ++iy)
{
for (int ix = 0; ix < nWidth; ++ix)
{
Color nc = GetNearestBaseColor(pBuffer[0].FromOle());

pBuffer[0] &= (uint)((uint)nc.A << 24) | //A
(uint)(nc.R << 16 ) | //R
(uint)(nc.G << 8 ) | //G
(uint)(nc.B ); //B
++pBuffer;
}
pBuffer += nOffset;
}
}

Or, if you’re in WPF and .NET 3.5 create simple pixel shader effect to do it for you in hardware. Now, my colleague can do it himself in about 5 minutes :) . Have a nice day and be good people.

Bootstrapper for .NET framework version detector

You wrote your .NET program, that can be used as stand alone portable application (such as it should be for Smart Client Apps), however you have to be sure, that necessary prerequisites (such as .NET framework) are installed on client’s machine. What to do? How to detect .NET framework version installed on target machine before running .NET application. The answer is – to use unmanaged C++ bootstrapper, that invoke your application if correct version of framework is installed.

.NET framework vrsion detector

Until now there are 15 possible .NET frameworks can be installed on client’s machine. Here the table of possible and official supported versions, as appears in Q318785

.NET version Actual version
3.5 SP1 3.5.30729.1
3.5 3.5.21022.8
3.0 SP2 3.0.4506.2152
3.0 SP1 3.0.4506.648
3.0 3.0.4506.30
2.0 SP2 2.0.50727.3053
2.0 SP1 2.0.50727.1433
2.0 2.0.50727.42
1.1 SP1 1.1.4322.2032
1.1 SP1 (in 32 bit version of Windows 2003) 1.1.4322.2300
1.1 1.1.4322.573
1.0 SP3 1.0.3705.6018
1.0 SP2 1.0.3705.288
1.0 SP1 1.0.3705.209
1.0 1.0.3705.0

All of those versions are detectible by queering specific registry keys. However, in some cases, you need to load mscoree.dll and call “GETCOREVERSION” API to determine whether specific version of .NET is installed. You can read more about it in MSDN.

So it’s really simple to write small C++ application (or PowerShell applet), that queries registry and invoke your managed application. How to do this? You can either read about it in outstanding blog of Aaron Stebner, who is Project Manager in XNA platform deployment team or attend my session next week to learn do it yourself. We’ll speak about nifty ways to do it also.

Anyway, by now, you can use small stand alone program, I wrote a while ago, that will tell you all versions of .NET frameworks installed in target machine without any prerequisites. It can be run even from shared network location :)

Download whoooot.exe (13K) >>

See you next week.

PS: Do not forget to download and install the new version of Visual Studio Snippet Designer, which is extremely useful tool by MVP Bill McCarthy, you’ll need it later next week…

Have a nice day and be good people.

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