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Lazy Alternatives - LazyAndWeak and BackgroundLoader

, 1 Dec 2011
This article will present two alternatives to Lazy.
LazyAlternatives.zip
LazyAlternatives
LazyAlternatives.suo
LazyAlternativesSample
Properties
Settings.settings
Pfz
Caching
Collections
DataTypes
DynamicObjects
Internal
Extensions
Factoring
Pfz.csproj.user
Pfz.Phone.csproj.user
Pfz.ruleset
Pfz.Silverlight.csproj.user
Pfz.snk
Pfz.suo
PhoneSpecific
Properties
Remoting
Instructions
Internal
Serializers
Udp
Serialization
BinaryBuiltIn
Threading
Contexts
Disposers
Unsafe
using System;
using System.Diagnostics.CodeAnalysis;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace Pfz.Remoting
{
	/// <summary>
	/// This is a class that transforms a simple (non-encrypted) stream into an
	/// encrypted one. <br/>
	/// It does: Create an assymetric private key (on server), sends the public
	/// part to the client and, then, the client creates a new symmetric key that 
	/// is known is sent to the server using the asmmetric key.<br/>
	/// After that, only the symmetric algorithm is used, as it is faster,
	/// but it is guaranteed that only the server and the client knows the key.<br/>
	/// This cryptography guarantees that no one "sniffing" the network would be
	/// able to interpret the messages, but does not guarantees that the requested
	/// host is really the host it should be. To that additional verification,
	/// you would probably need to deal with certificates and the SslStream.
	/// </summary>
	public class SecureStream:
		Stream
	{
		#region Fields
			private static readonly byte[] _emptyReadBuffer = new byte[0];
			private MemoryStream _writeBuffer;
		#endregion

		#region Constructors
			/// <summary>
			/// Creates a new secure stream (stream that uses an assymetric key to
			/// initialize and then a symmetric key to continue it's work) over another
			/// stream, without any other parameters, so, running as client.
			/// </summary>
			[SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope")]
			public SecureStream(Stream baseStream):
				this(baseStream, new RSACryptoServiceProvider(), SymmetricAlgorithm.Create(), false)
			{
			}

			/// <summary>
			/// Creates a new secure stream (stream that uses an assymetric key to
			/// initialize and then a symmetric key to continue it's work) over another
			/// stream, specifying if running as client or server, but without changing
			/// the default symmetric or assymetric class/algorithm..
			/// </summary>
			[SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope")]
			public SecureStream(Stream baseStream, bool runAsServer):
				this(baseStream, new RSACryptoServiceProvider(), SymmetricAlgorithm.Create(), runAsServer)
			{
			}
		
			/// <summary>
			/// Creates a new secure stream (stream that uses an assymetric key to
			/// initialize and then a symmetric key to continue it's work) over another
			/// stream. <br/>
			/// Species the symmetricAlgorithm to use.
			/// </summary>
			[SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope")]
			public SecureStream(Stream baseStream, SymmetricAlgorithm symmetricAlgorithm):
				this(baseStream, new RSACryptoServiceProvider(), symmetricAlgorithm, false, 2048)
			{
			}
		
			/// <summary>
			/// Creates a new secure stream (stream that uses an assymetric key to
			/// initialize and then a symmetric key to continue it's work) over another
			/// stream. <br/>
			/// Species the symmetricAlgorithm to use and if it runs as a client or server.
			/// </summary>
			[SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope")]
			public SecureStream(Stream baseStream, SymmetricAlgorithm symmetricAlgorithm, bool runAsServer):
				this(baseStream, new RSACryptoServiceProvider(), symmetricAlgorithm, runAsServer, 2048)
			{
			}

			/// <summary>
			/// Creates a new secure stream (stream that uses an assymetric key to
			/// initialize and then a symmetric key to continue it's work) over another
			/// stream. <br/>
			/// Specifies the assymetric and the symmetric algorithm to use, and if it 
			/// must run as client or server.
			/// </summary>
			public SecureStream(Stream baseStream, RSACryptoServiceProvider rsa, SymmetricAlgorithm symmetricAlgorithm, bool runAsServer):
				this(baseStream, rsa, symmetricAlgorithm, runAsServer, 2048)
			{
			}

			/// <summary>
			/// Creates a new secure stream (stream that uses an assymetric key to
			/// initialize and then a symmetric key to continue it's work) over another
			/// stream. <br/>
			/// Specifies the assymetric and the symmetric algorithm to use, if it 
			/// must run as client or server and the writeBufferInitialLength.
			/// </summary>
			public SecureStream(Stream baseStream, RSACryptoServiceProvider rsa, SymmetricAlgorithm symmetricAlgorithm, bool runAsServer, int writeBufferInitialLength)
			{
				if (baseStream == null)
					throw new ArgumentNullException("baseStream");
			
				if (rsa == null)
					throw new ArgumentNullException("rsa");
				
				if (symmetricAlgorithm == null)
					throw new ArgumentNullException("symmetricAlgorithm");
				
				if (writeBufferInitialLength < 0)
					throw new ArgumentException("writeBufferInitialLength must can't be negative.", "writeBufferInitialLength");
		
				BaseStream = baseStream;
				SymmetricAlgorithm = symmetricAlgorithm;

				string symmetricTypeName = symmetricAlgorithm.GetType().ToString();
				byte[] symmetricTypeBytes = Encoding.UTF8.GetBytes(symmetricTypeName);
				if (runAsServer)
				{
					byte[] sizeBytes = BitConverter.GetBytes(symmetricTypeBytes.Length);
					baseStream.Write(sizeBytes, 0, sizeBytes.Length);
					baseStream.Write(symmetricTypeBytes, 0, symmetricTypeBytes.Length);
			
					byte[] bytes = rsa.ExportCspBlob(false);
					sizeBytes = BitConverter.GetBytes(bytes.Length);
					baseStream.Write(sizeBytes, 0, sizeBytes.Length);
					baseStream.Write(bytes, 0, bytes.Length);
				
					symmetricAlgorithm.Key = _ReadWithLength(rsa);;
					symmetricAlgorithm.IV = _ReadWithLength(rsa);
				}
				else
				{
					// ok. We run as the client, so first we first check the
					// algorithm types and then receive the assymetric
					// key from the server.
				
					// symmetricAlgorithm
					var sizeBytes = new byte[4];
					_ReadDirect(sizeBytes);
					var stringLength = BitConverter.ToInt32(sizeBytes, 0);
				
					if (stringLength != symmetricTypeBytes.Length)
						throw new ArgumentException("Server and client must use the same SymmetricAlgorithm class.");
				
					var stringBytes = new byte[stringLength];
					_ReadDirect(stringBytes);
					var str = Encoding.UTF8.GetString(stringBytes);
					if (str != symmetricTypeName)
						throw new ArgumentException("Server and client must use the same SymmetricAlgorithm class.");

					// public key.
					sizeBytes = new byte[4];
					_ReadDirect(sizeBytes);
					int asymmetricKeyLength = BitConverter.ToInt32(sizeBytes, 0);
					byte[] bytes = new byte[asymmetricKeyLength];
					_ReadDirect(bytes);
					rsa.ImportCspBlob(bytes);
				
					// Now that we have the asymmetricAlgorithm set, and considering
					// that the symmetricAlgorithm initializes automatically, we must
					// only send the key.
					_WriteWithLength(rsa, symmetricAlgorithm.Key);
					_WriteWithLength(rsa, symmetricAlgorithm.IV);
				}
			
				// After the object initialization being done, be it a client or a
				// server, we can dispose the assymetricAlgorithm.
				rsa.Clear();
			
				Decryptor = symmetricAlgorithm.CreateDecryptor();
				Encryptor = symmetricAlgorithm.CreateEncryptor();
			
				_readBuffer = _emptyReadBuffer;
				_writeBuffer = new MemoryStream(writeBufferInitialLength);
 			}
		#endregion
		#region Dispose
			/// <summary>
			/// Releases the buffers, the basestream and the cryptographic classes.
			/// </summary>
			protected override void Dispose(bool disposing)
			{
				if (disposing)
				{
					Disposer.Dispose(ref _writeBuffer);
				
					var encryptor = this.Encryptor;
					if (encryptor != null)
					{
						Encryptor = null;
						encryptor.Dispose();
					}
				
					var decryptor = this.Decryptor;
					if (decryptor != null)
					{
						Decryptor = null;
						decryptor.Dispose();
					}
				
					var symmetricAlgorithm = SymmetricAlgorithm;
					if (symmetricAlgorithm != null)
					{
						SymmetricAlgorithm = null;
						symmetricAlgorithm.Clear();
					}
				
					var baseStream = this.BaseStream;
					if (baseStream != null)
					{
						BaseStream = null;
						baseStream.Dispose();
					}
				
					_readBuffer = null;
				}
		
				base.Dispose(disposing);
			}
		#endregion

		#region Properties
			/// <summary>
			/// Gets the original stream that created this asymmetric crypto stream.
			/// </summary>
			public Stream BaseStream { get; private set; }
		
			/// <summary>
			/// Gets the symmetric algorithm being used.
			/// </summary>
			public SymmetricAlgorithm SymmetricAlgorithm { get; private set; }
		
			/// <summary>
			/// Gets the encryptor being used.
			/// </summary>
			public ICryptoTransform Decryptor { get; private set; }
		
			/// <summary>
			/// Gets the decryptor being used.
			/// </summary>
			public ICryptoTransform Encryptor { get; private set; }
		
			/// <summary>
			/// Always returns true.
			/// </summary>
			public override bool CanRead
			{
				get
				{
					return true;
				}
			}

			/// <summary>
			/// Always returns false.
			/// </summary>
			public override bool CanSeek
			{
				get
				{
					return false;
				}
			}

			/// <summary>
			/// Always returns true.
			/// </summary>
			public override bool CanWrite
			{
				get
				{
					return true;
				}
			}


			/// <summary>
			/// Throws a NotSupportedException.
			/// </summary>
			public override long Length
			{
				get
				{
					throw new NotSupportedException();
				}
			}

			/// <summary>
			/// Throws a NotSupportedException.
			/// </summary>
			public override long Position
			{
				get
				{
					throw new NotSupportedException();
				}
				set
				{
					throw new NotSupportedException();
				}
			}

			/// <summary>
			/// Gets or sets the time-out for reads.
			/// </summary>
			public override int ReadTimeout
			{
				get
				{
					return BaseStream.ReadTimeout;
				}
				set
				{
					BaseStream.ReadTimeout = value;
				}
			}

			/// <summary>
			/// Gets or sets the time-out for writes.
			/// </summary>
			public override int WriteTimeout
			{
				get
				{
					return BaseStream.WriteTimeout;
				}
				set
				{
					BaseStream.WriteTimeout = value;
				}
			}

			/// <summary>
			/// Gets a value indicating if this stream supports timed-out operations.
			/// </summary>
			public override bool CanTimeout
			{
				get
				{
					return BaseStream.CanTimeout;
				}
			}
		#endregion
		#region Methods
			#region Read
				private readonly byte[] _sizeBytes = new byte[5];
				private int _readPosition;
				private byte[] _readBuffer;
				private byte _readCRC;
				/// <summary>
				/// Reads and decryptographs the given number of bytes from the buffer.
				/// </summary>
				public override int Read(byte[] buffer, int offset, int count)
				{
					if (_readPosition == _readBuffer.Length)
					{
						_ReadDirect(_sizeBytes);
						int readLength = BitConverter.ToInt32(_sizeBytes, 0);
				
						if (_readBuffer.Length < readLength)
							_readBuffer = new byte[readLength];
					
						_FullReadDirect(_readBuffer, readLength);
						_readBuffer = Decryptor.TransformFinalBlock(_readBuffer, 0, readLength);
				
						// here we check if our actual CRC is the same as the message CRC.
						byte crc = _sizeBytes[4];
						if (crc != _readCRC)
							throw new IOException("Invalid CRC.");
					
						// And after we decrypt the message with such crc.
						int readBufferLength = _readBuffer.Length;
						for(int i=0; i<readBufferLength; i++)
						{
							byte newCrc = _readBuffer[i];
							_readBuffer[i] ^= crc;
							crc = newCrc;
						}
				
						_readCRC = crc;
						_readPosition = 0;
					}
			
					int diff = _readBuffer.Length - _readPosition;
					if (count > diff)
						count = diff;
			
					Buffer.BlockCopy(_readBuffer, _readPosition, buffer, offset, count);
					_readPosition += count;
					return count;
				}
			#endregion
			#region Write
				/// <summary>
				/// Encrypts and writes the given bytes.
				/// </summary>
				public override void Write(byte[] buffer, int offset, int count)
				{
					_writeBuffer.Write(buffer, offset, count);
				}
			#endregion
			#region Flush
				private int _maxLength;
				private int _collectionNumber = GC.CollectionCount(GC.MaxGeneration);
				private byte _writeCRC;
				/// <summary>
				/// Sends all the buffered data.
				/// </summary>
				public override void Flush()
				{
					int length = (int)_writeBuffer.Length;
					if (length > 0)
					{
						// here we pre-encrypt the block and generate a CRC. We do this so
						// two identical blocks will, in fact, be different.
						var writeBuffer = _writeBuffer.GetBuffer();
						byte crc = _writeCRC;
						for (int i=0; i<length; i++)
						{
							crc ^= writeBuffer[i];
							writeBuffer[i] = crc;
						}
			
						var encryptedBuffer = Encryptor.TransformFinalBlock(writeBuffer, 0, length);
						var size = BitConverter.GetBytes(encryptedBuffer.Length);
						BaseStream.Write(size, 0, size.Length);
						BaseStream.WriteByte(_writeCRC);
						BaseStream.Write(encryptedBuffer, 0, encryptedBuffer.Length);
						BaseStream.Flush();
				
						_writeCRC = crc;
						_writeBuffer.SetLength(0);
				
						int collectionNumber = GC.CollectionCount(GC.MaxGeneration);
						if (collectionNumber == _collectionNumber)
						{
							if (length > _maxLength)
								_maxLength = length;
						}
						else
						{
							if (_maxLength != 0)
							{
								int halfLength = _writeBuffer.Capacity / 2;
								if (_maxLength < halfLength)
									_writeBuffer.Capacity = _maxLength + (_maxLength / 2);
							
								_maxLength = 0;
							}
					
							_collectionNumber = collectionNumber;
						}
					}
				}
			#endregion

			#region _ReadDirect
				private void _ReadDirect(byte[] bytes)
				{
					_FullReadDirect(bytes, bytes.Length);
				}
				private void _FullReadDirect(byte[] bytes, int length)
				{
					int read = 0;
					while(read < length)
					{
						int readResult = BaseStream.Read(bytes, read, length - read);
				
						if (readResult == 0)
							throw new IOException("The stream was closed by the remote side.");
				
						read += readResult;
					}
				}
			#endregion
			#region _ReadWithLength
				private byte[] _ReadWithLength(RSACryptoServiceProvider rsa)
				{
					byte[] size = new byte[4];
					_ReadDirect(size);
		
					int count = BitConverter.ToInt32(size, 0);
					var bytes = new byte[count];
					_ReadDirect(bytes);
			
					return rsa.Decrypt(bytes, false);
				}
			#endregion
			#region _WriteWithLength
				private void _WriteWithLength(RSACryptoServiceProvider rsa, byte[] bytes)
				{
					bytes = rsa.Encrypt(bytes, false);
					byte[] sizeBytes = BitConverter.GetBytes(bytes.Length);
					BaseStream.Write(sizeBytes, 0, sizeBytes.Length);
					BaseStream.Write(bytes, 0, bytes.Length);
				}
			#endregion

			#region Not Supported Methods
				/// <summary>
				/// Throws a NotSupportedException.
				/// </summary>
				public override long Seek(long offset, SeekOrigin origin)
				{
					throw new NotSupportedException();
				}

				/// <summary>
				/// Throws a NotSupportedException.
				/// </summary>
				public override void SetLength(long value)
				{
					throw new NotSupportedException();
				}
			#endregion
		#endregion
	}
}

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About the Author

Paulo Zemek
Architect
Canada Canada
I started to program computers when I was 11 years old, as a hobbist, programming in AMOS Basic and Blitz Basic for Amiga.
At 12 I had my first try with assembler, but it was too difficult at the time. Then, in the same year, I learned C and, after learning C, I was finally able to learn assembler (for Motorola 680x0).
Not sure, but probably between 12 and 13, I started to learn C++. I always programmed "in an object oriented way", but using function pointers instead of virtual methods.
 
At 15 I started to learn Pascal at school and to use Delphi. At 16 I started my first internship (using Delphi). At 18 I started to work professionally using C++ and since then I've developed my programming skills as a professional developer in C++ and C#, generally creating libraries that help other developers do they work easier, faster and with less errors.
 
Want more info or simply want to contact me?
Take a look at: http://paulozemek.azurewebsites.net/
Or e-mail me at: paulozemek@outlook.com
 
Codeproject MVP 2012
Microsoft MVP 2013

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