diff --git a/Lecture/Lecture.sln.GhostDoc.user.dic b/Lecture/Lecture.sln.GhostDoc.user.dic
index 320f3457..fae487ca 100644
--- a/Lecture/Lecture.sln.GhostDoc.user.dic
+++ b/Lecture/Lecture.sln.GhostDoc.user.dic
@@ -1,3 +1,4 @@
+Crypto
 csharp
 Globalization
 Hermetization
diff --git a/Lecture/P03.DataStreams/DataStreams.UnitTest/CryptographyHelpersUnitTest.cs b/Lecture/P03.DataStreams/DataStreams.UnitTest/CryptographyHelpersUnitTest.cs
new file mode 100644
index 00000000..7bbb010b
--- /dev/null
+++ b/Lecture/P03.DataStreams/DataStreams.UnitTest/CryptographyHelpersUnitTest.cs
@@ -0,0 +1,89 @@
+//____________________________________________________________________________
+//
+//  Copyright (C) 2018, Mariusz Postol LODZ POLAND.
+//
+//  To be in touch join the community at GITTER: https://gitter.im/mpostol/TP
+//____________________________________________________________________________
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System.Diagnostics;
+using System.IO;
+using System.Security.Cryptography;
+using System.Xml;
+
+namespace TP.DataStreams.Cryptography
+{
+  [TestClass]
+  public class CryptographyHelpersUnitTest
+  {
+    [TestMethod]
+    public void CalculateSHA256Test()
+    {
+      const string _pasword = "Fe4ZFH2VgpOOwBdM9dkI";
+      (string HexString, string Base64) = _pasword.CalculateSHA256();
+      Assert.AreEqual<string>("D9CBFBB0AD87D8CE0CC0D2FF1BCFF67C6933D2B4B4CC4C6FA60CE29F73322CD8", HexString);
+      Assert.AreEqual<int>(256/4, HexString.Length);
+      Assert.AreEqual<string>("2cv7sK2H2M4MwNL/G8/2fGkz0rS0zExvpgzin3MyLNg=", Base64);
+      Assert.AreEqual<int>(44, Base64.Length);
+    }
+    [TestMethod]
+    public void CalculateSHA256LongTest()
+    {
+      const string _pasword = "UAXflAoVz8wcR1VkxUgTO8HAMBYK83yQvcHI9nqsQUiI4mx6jLlCAFGPrHj99XHi3uOoUfqe7wF7JkX2wBwwPADpn9f8s2Q0CfaA";
+      (string HexString, string Base64) = _pasword.CalculateSHA256();
+      Assert.AreEqual<string>("B77B064339A0D98C722F54A7B055539BD63BAFC07EBD2B9342EA247EAA86FB18", HexString);
+      Assert.AreEqual<int>(256 / 4, HexString.Length);
+      Assert.AreEqual<string>("t3sGQzmg2YxyL1SnsFVTm9Y7r8B+vSuTQuokfqqG+xg=", Base64);
+      Assert.AreEqual<int>(44, Base64.Length);
+    }
+    [TestMethod]
+    public void XmlSignatureTestMethod1()
+    {
+      (RSAParameters parameters, string publicKey, string privatePublicKeys) = CreateRSACryptoServiceKeys();
+      Assert.IsNotNull(parameters);
+      Assert.AreNotEqual<string>(publicKey, privatePublicKeys);
+      Debug.WriteLine(publicKey);
+      Debug.WriteLine(string.Empty);
+      Debug.WriteLine(privatePublicKeys);
+    }
+    [TestMethod]
+    [DeploymentItem("Instrumentation")]
+    public void XmlSignatureTest()
+    {
+      const string _xmlFile = @"catalog.example.xml";
+      Assert.IsTrue(File.Exists(_xmlFile));
+      const string _publiKey = @"PubliKey.xml";
+      Assert.IsTrue(File.Exists(_publiKey));
+      const string _publiPrivateKeys = @"PubliPrivateKeys.xml";
+      Assert.IsTrue(File.Exists(_publiPrivateKeys));
+      XmlDocument _documentToSign = new XmlDocument();
+      _documentToSign.Load(_xmlFile);
+      const string _signedFileName = "SignedXmlFile.xml";
+      string _rsaKeys = null;
+      if (File.Exists(_signedFileName))
+        File.Delete(_signedFileName);
+      using (StreamReader _reader = new StreamReader(_publiPrivateKeys, System.Text.Encoding.UTF8))
+        _rsaKeys = _reader.ReadToEnd();
+      CryptographyHelpers.SignSaveXml(_documentToSign, _rsaKeys, _signedFileName);
+      Assert.IsTrue(File.Exists(_signedFileName));
+      XmlDocument _signedXmlDocument1 = CryptographyHelpers.LoadVerifyXml(_signedFileName);
+      Assert.IsNotNull(_signedXmlDocument1);
+      using (StreamReader _reader = new StreamReader(_publiKey, System.Text.Encoding.UTF8))
+        _rsaKeys = _reader.ReadToEnd();
+      XmlDocument _signedXmlDocument2 = CryptographyHelpers.LoadVerifyXml(_rsaKeys, _signedFileName);
+      Assert.IsNotNull(_signedXmlDocument2);
+      Assert.AreEqual<string>(_signedXmlDocument1.ToString(), _signedXmlDocument2.ToString());
+    }
+    private (RSAParameters parameters, string publicKey, string privatePublicKeys) CreateRSACryptoServiceKeys()
+    {
+      using (RSACryptoServiceProvider _rsa = new RSACryptoServiceProvider(2048))
+      {
+        RSAParameters _parameters = _rsa.ExportParameters(true);
+        string _public = _rsa.ToXmlString(false);
+        string _both = _rsa.ToXmlString(true);
+        return (_parameters, _public, _both);
+      }
+    }
+  }
+}
+
diff --git a/Lecture/P03.DataStreams/DataStreams.UnitTest/DataStreams.UnitTest.csproj b/Lecture/P03.DataStreams/DataStreams.UnitTest/DataStreams.UnitTest.csproj
index 8514464c..60349934 100644
--- a/Lecture/P03.DataStreams/DataStreams.UnitTest/DataStreams.UnitTest.csproj
+++ b/Lecture/P03.DataStreams/DataStreams.UnitTest/DataStreams.UnitTest.csproj
@@ -62,6 +62,7 @@
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="FileStreamUnitTest.cs" />
     <Compile Include="ReflectionUnitTest.cs" />
+    <Compile Include="CryptographyHelpersUnitTest.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="Instrumentation\Catalog.xsd">
@@ -78,13 +79,25 @@
     </ProjectReference>
   </ItemGroup>
   <ItemGroup>
-    <None Include="Instrumentation\catalog.example.xml" />
+    <None Include="Instrumentation\catalog.example.xml">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
   </ItemGroup>
   <ItemGroup>
     <None Include="Instrumentation\Catalog.xslt">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
   </ItemGroup>
+  <ItemGroup>
+    <Content Include="Instrumentation\PubliKey.xml">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+      <SubType>Designer</SubType>
+    </Content>
+    <Content Include="Instrumentation\PubliPrivateKeys.xml">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+      <SubType>Designer</SubType>
+    </Content>
+  </ItemGroup>
   <Import Project="$(VSToolsPath)\TeamTest\Microsoft.TestTools.targets" Condition="Exists('$(VSToolsPath)\TeamTest\Microsoft.TestTools.targets')" />
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
diff --git a/Lecture/P03.DataStreams/DataStreams.UnitTest/Instrumentation/PubliKey.xml b/Lecture/P03.DataStreams/DataStreams.UnitTest/Instrumentation/PubliKey.xml
new file mode 100644
index 00000000..0aa2021b
--- /dev/null
+++ b/Lecture/P03.DataStreams/DataStreams.UnitTest/Instrumentation/PubliKey.xml
@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<RSAKeyValue>
+  <Modulus>2oFiov7xnJGWf++WBHOdkzp1IHzNZRXhFL0MDFxBIJQvlm3p80WwhoxUQVawJTGRbdGMutOHHOTj+uxFAFlmKrvcaltfRV/rq0Z43LeIbfeX8uwsr10lnxqLhONlP+kY9+RiAartXP3nTG88gFah9j7WrSmlrJWvSCD0lZvUxcuFioXXZw8UQ43046SWhXMYABkZ+1RYKsSjfz80/TITuR0kkY3wIwHiIWhZUjWwNxEh0CLmM06oFLjSKgZwe4UyhCRlg3iXNK3CeMC+ToSyo+lehGnWD226uNECvB3SWC4YN7r96u0xrQcf0//x6nzSdEArohFVyGgB3yb6rlFLjw==</Modulus>
+  <Exponent>AQAB</Exponent>
+</RSAKeyValue>
\ No newline at end of file
diff --git a/Lecture/P03.DataStreams/DataStreams.UnitTest/Instrumentation/PubliPrivateKeys.xml b/Lecture/P03.DataStreams/DataStreams.UnitTest/Instrumentation/PubliPrivateKeys.xml
new file mode 100644
index 00000000..cf36930d
--- /dev/null
+++ b/Lecture/P03.DataStreams/DataStreams.UnitTest/Instrumentation/PubliPrivateKeys.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<RSAKeyValue>
+  <Modulus>2oFiov7xnJGWf++WBHOdkzp1IHzNZRXhFL0MDFxBIJQvlm3p80WwhoxUQVawJTGRbdGMutOHHOTj+uxFAFlmKrvcaltfRV/rq0Z43LeIbfeX8uwsr10lnxqLhONlP+kY9+RiAartXP3nTG88gFah9j7WrSmlrJWvSCD0lZvUxcuFioXXZw8UQ43046SWhXMYABkZ+1RYKsSjfz80/TITuR0kkY3wIwHiIWhZUjWwNxEh0CLmM06oFLjSKgZwe4UyhCRlg3iXNK3CeMC+ToSyo+lehGnWD226uNECvB3SWC4YN7r96u0xrQcf0//x6nzSdEArohFVyGgB3yb6rlFLjw==</Modulus>
+  <Exponent>AQAB</Exponent>
+  <P>9A0KwiudcPWDrwVIq+2ANkuu7IILGf9D94U+qViZAKclqxc9+7UcCeP1a0LCmTiJCVLvNam4ISvU3I7rBnE46cFvJ7c+9SIQZTfb9HOFB78Q5+ulx9k9lv8VKypfuBynoV15f3OHkr2FddSsyKf4EuF20UVWsV8YSJ+iJ5gCc8M=</P>
+  <Q>5TQnMXCb2DjgY1sGfQgaOtVOakjemhkGUeKNJ+4ptcTUHp/hZWPtZw53kFdje1fZprDdMqKIxM2XQI+NDm2WIDnBOsXQK+K1LAh+4XXEBS+0HcPqqMW8itttOXLeoiNDXWwYWQ5/6UOLUC1ZGyjynE89FQKpyp2i6pHWhocuCEU=</Q>
+  <DP>xoXhbYfLH7snrnSu4+RjukcgeRVj8Hbck/mYumrus0BEfQOAEUQHFeiQl/sLj1YU6zfCjLWNqbYdBnlfp7LsaAJI6FbA6OkXyy6ARz69RUrgdrgS+Bm4Zx8C2kUy7fKpTbNbBRk2fGCcsvgYwXUZcEplu+AaoFhJybHJV0npHL8=</DP>
+  <DQ>LH4tRYmolxajaGYZIlhaTyVtLXCr1ZoaAfdKk3/GFQT6cF9076uwQBss1pZAN4dcNuGKbvPiPOH0BJJZPX3EcMkFW5VezcYaiUu05atou+EAw+5uNQj9iq8Byu8jjLHvt8juCQuphOyZtJy4+W6/edxf7R4xO6XSJFrfHApNw0k=</DQ>
+  <InverseQ>0op7bysIJnOESr0FO8JxVh85wK0dX4vC89prAzUPc2YBsrf4aW/tSewcHDtGvx0fuUZEiJcyzunho+cuuC3SzMZK2CXTJWIvR/qTuD5bjzWm3CNKP+AdvLTaCQ78M/fx7D96bhPECsy2rkwh3iBCNs0YytrGkmeij9V6Pe0ZYRk=</InverseQ>
+  <D>QkBexuskGQPvrQTY6KqhiYV9BAezQ0YaA+66G3lRae5ka2kSOWfU+UbNOS5upCheXvzdfbwrSHCCS4+d8Fgq6SQi1cC0p1VJIJpyhQHFBQrAcLB5cAZ/JLmoufc0uOcVYfxGVxkbdUmq+vrzTjp2SzKMZt6s1CJiji0n28DvB7V5XpZoCBVAyT705jtdx/K5zgYd7a036D5e2KNtBWDI2l2w63AAQNaqgsNGjEt3N1fHO1yyOf9q7loYvtNAJcj5i2TpEeWiJy5w1hfYGfG28bB+mrL71dfG7wjJWrUJNdoKeONS63ZS2jwMyeTWp5wuwwlh8cgQMXhJBlJF9lPNeQ==</D>
+</RSAKeyValue>
+
diff --git a/Lecture/P03.DataStreams/DataStreams.UnitTest/SerializationUnitTest.cs b/Lecture/P03.DataStreams/DataStreams.UnitTest/SerializationUnitTest.cs
index ce6a8ce0..2ae6e7ac 100644
--- a/Lecture/P03.DataStreams/DataStreams.UnitTest/SerializationUnitTest.cs
+++ b/Lecture/P03.DataStreams/DataStreams.UnitTest/SerializationUnitTest.cs
@@ -42,7 +42,7 @@ public void ReadWRiteTest()
       Catalog _catalog2Write = new Catalog();
       _catalog2Write.AddTestingData();
       Assert.IsNotNull(_catalog2Write.CD);
-      string _fileName = @"Instrumentation\catalog.xml";
+      string _fileName = @"catalog.xml";
       XmlFile.WriteXmlFile<Catalog>(_catalog2Write, _fileName, FileMode.Create);
       Catalog _recoveredCatalog = XmlFile.ReadXmlFile<Catalog>(_fileName);
       Assert.IsNotNull(_recoveredCatalog);
diff --git a/Lecture/P03.DataStreams/DataStreams/Cryptography/CryptographyHelpers.cs b/Lecture/P03.DataStreams/DataStreams/Cryptography/CryptographyHelpers.cs
new file mode 100644
index 00000000..7447146e
--- /dev/null
+++ b/Lecture/P03.DataStreams/DataStreams/Cryptography/CryptographyHelpers.cs
@@ -0,0 +1,164 @@
+//____________________________________________________________________________
+//
+//  Copyright (C) 2018, Mariusz Postol LODZ POLAND.
+//
+//  To be in touch join the community at GITTER: https://gitter.im/mpostol/TP
+//____________________________________________________________________________
+
+using System;
+using System.IO;
+using System.Security.Cryptography;
+using System.Security.Cryptography.Xml;
+using System.Text;
+using System.Xml;
+
+namespace TP.DataStreams.Cryptography
+{
+
+  public static class CryptographyHelpers
+  {
+    public static (string Hex, string Base64) CalculateSHA256 (this string inputStream)
+    {
+      byte[] _inputStreamBytes = Encoding.UTF8.GetBytes(inputStream);
+      using (SHA256 mySHA256 = SHA256Managed.Create())
+      {
+        byte[] hashValue = mySHA256.ComputeHash(_inputStreamBytes);
+        return (hashValue.ToHexString(), Convert.ToBase64String(hashValue, Base64FormattingOptions.InsertLineBreaks));
+      }
+    }
+    public static void EncryptData(string inFileName, string outFileName, byte[] dESKey, byte[] dESIV, IProgress<long> progress)
+    {
+      //Create the file streams to handle the input and output files.
+      using (FileStream _inFileStream = new FileStream(inFileName, FileMode.Open, FileAccess.Read))
+      {
+        using (FileStream _outFileStream = new FileStream(outFileName, FileMode.OpenOrCreate, FileAccess.Write))
+        {
+          _outFileStream.SetLength(0);
+          //Create variables to help with read and write.
+          byte[] _buffer = new byte[100]; //This is intermediate storage for the encryption.
+          long _bytesWritten = 0; //This is the total number of bytes written.
+          long _inFileStreamLength = _inFileStream.Length; //This is the total length of the input file.
+          int _length; //This is the number of bytes to be written at a time.
+          TripleDESCryptoServiceProvider _tripleProvider = new TripleDESCryptoServiceProvider();
+          using (CryptoStream _outCryptoStream = new CryptoStream(_outFileStream, _tripleProvider.CreateEncryptor(dESKey, dESIV), CryptoStreamMode.Write))
+          {
+            //Read from the input file, then encrypt and write to the output file.
+            while (_bytesWritten < _inFileStreamLength)
+            {
+              _length = _inFileStream.Read(_buffer, 0, 100);
+              _outCryptoStream.Write(_buffer, 0, _length);
+              _bytesWritten = _bytesWritten + _length;
+              progress.Report(_bytesWritten);
+            }
+          }
+        }
+      }
+    }
+    /// <summary>
+    /// Sign and save an XML document.
+    /// </summary>
+    /// <param name="document">Document to be signed</param>
+    /// <param name="rsa">The keys ro be used by the <see cref="RSACryptoServiceProvider"/> RSA algorithm implementation.</param>
+    /// <remarks>
+    /// This document cannot be verified unless the verifying code has the public key with which it was signed.
+    /// </remarks>
+    public static void SignSaveXml(this XmlDocument document, string rsaKeys, string fileName)
+    {
+      #region Check arguments
+      if (document == null)
+        throw new ArgumentException($"The {nameof(document)} parameter cannot be null");
+      if (string.IsNullOrEmpty(rsaKeys))
+        throw new ArgumentException($"The {nameof(rsaKeys)} parameter cannot be null");
+      if (string.IsNullOrEmpty(fileName))
+        throw new ArgumentException($"The {nameof(fileName)} parameter cannot be null");
+      #endregion
+      using (RSACryptoServiceProvider _rsaProvider = new RSACryptoServiceProvider())
+      {
+        _rsaProvider.FromXmlString(rsaKeys);
+        KeyInfo _keyInfo = new KeyInfo();// Add an RSAKeyValue KeyInfo (optional; helps recipient find key to validate).
+        _keyInfo.AddClause(new RSAKeyValue(_rsaProvider));
+        SignedXml _signedXml = new SignedXml(document)
+        {
+          SigningKey = _rsaProvider, // Add the key to the SignedXml document.
+          KeyInfo = _keyInfo
+        };
+        Reference _reference = new Reference // Create a reference to be signed.
+        {
+          Uri = "" //An entire XML document is to be signed using an enveloped signature.
+        };
+        XmlDsigEnvelopedSignatureTransform _envelope = new XmlDsigEnvelopedSignatureTransform(); // Add an enveloped transformation to the reference.
+        _reference.AddTransform(_envelope);
+        _signedXml.AddReference(_reference); // Add the reference to the SignedXml object.
+        _signedXml.ComputeSignature(); // Compute the signature.
+        XmlElement _xmlDigitalSignature = _signedXml.GetXml(); // Get the XML representation of the signature and save it to an XmlElement object.
+        document.DocumentElement.AppendChild(document.ImportNode(_xmlDigitalSignature, true));// Append the element to the XML document.
+      }
+      document.Save(fileName);
+    }
+    /// <summary>
+    /// Load and verify the signature of an XML file against an asymmetric RSA algorithm and return the document.
+    /// </summary>
+    /// <param name="rsaKeys">The RSA keys as the xml document.</param>
+    /// <param name="fileName">Name of the file.</param>
+    /// <returns>An instance of the <see cref="XmlDocument"/> capturing the xml file.</returns>
+    /// <exception cref="ArgumentException">
+    /// rsaKeys
+    /// or
+    /// fileName
+    /// </exception>
+    /// <exception cref="System.Security.Cryptography.CryptographicException"></exception>
+    /// <remarks>There must be only one signature.</remarks>
+    public static XmlDocument LoadVerifyXml(string rsaKeys, string fileName)
+    {
+      #region Check arguments
+      if (string.IsNullOrEmpty(rsaKeys))
+        throw new ArgumentException($"The {nameof(rsaKeys)} parameter cannot be null");
+      if (string.IsNullOrEmpty(fileName))
+        throw new ArgumentException($"The {nameof(fileName)} parameter cannot be null");
+      #endregion
+      (XmlDocument _document, SignedXml _signedXml) = LoadsIGNEDXmlFile(fileName);
+      using (RSACryptoServiceProvider _provider = new RSACryptoServiceProvider())
+      {
+        _provider.FromXmlString(rsaKeys);
+        if (!_signedXml.CheckSignature(_provider))// Check the signature and return the result.
+          throw new CryptographicException($"Wrong signature of the document.");
+      }
+      return _document;
+    }
+    public static XmlDocument LoadVerifyXml(string fileName)
+    {
+      #region Check arguments
+      if (string.IsNullOrEmpty(fileName))
+        throw new ArgumentException($"The {nameof(fileName)} parameter cannot be null");
+      #endregion
+      (XmlDocument _document, SignedXml _signedXml) = LoadsIGNEDXmlFile(fileName);
+      if (!_signedXml.CheckSignature())// Check the signature and return the result.
+        throw new System.Security.Cryptography.CryptographicException($"Wrong signature of the document.");
+      return _document;
+    }
+    private static string ToHexString(this byte[] bytes)
+    {
+      char[] c = new char[bytes.Length * 2];
+      int b;
+      for (int i = 0; i < bytes.Length; i++)
+      {
+        b = bytes[i] >> 4;
+        c[i * 2] = (char)(55 + b + (((b - 10) >> 31) & -7));
+        b = bytes[i] & 0xF;
+        c[i * 2 + 1] = (char)(55 + b + (((b - 10) >> 31) & -7));
+      }
+      return new string(c);
+    }
+    private static (XmlDocument document, SignedXml signedXml) LoadsIGNEDXmlFile(string fileName)
+    {
+      XmlDocument _document = new XmlDocument();
+      _document.Load(fileName);
+      SignedXml _signedXml = new SignedXml(_document);
+      XmlNodeList _nodeList = _document.GetElementsByTagName("Signature");// Find the "Signature" node and create a new XmlNodeList object.
+      if (_nodeList.Count != 1) // There must be only one signature. Return false if 0 or more than one signatures was found.
+        throw new CryptographicException($"Expected exactly one signature but the file contaons {_nodeList.Count}.");
+      _signedXml.LoadXml((XmlElement)_nodeList[0]);// Load the first <signature> node.
+      return (_document, _signedXml);
+    }
+  }
+}
\ No newline at end of file
diff --git a/Lecture/P03.DataStreams/DataStreams/DataStreams.csproj b/Lecture/P03.DataStreams/DataStreams/DataStreams.csproj
index d1c9c93d..7b3458e7 100644
--- a/Lecture/P03.DataStreams/DataStreams/DataStreams.csproj
+++ b/Lecture/P03.DataStreams/DataStreams/DataStreams.csproj
@@ -64,12 +64,31 @@
   <ItemGroup>
     <Reference Include="System" />
     <Reference Include="System.Core" />
+    <Reference Include="System.Data.OracleClient" />
+    <Reference Include="System.Drawing" />
+    <Reference Include="System.Net" />
+    <Reference Include="System.Security" />
+    <Reference Include="System.Security.AccessControl, Version=4.1.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\System.Security.AccessControl.4.5.0\lib\net461\System.Security.AccessControl.dll</HintPath>
+    </Reference>
+    <Reference Include="System.Security.Cryptography.Xml, Version=4.0.1.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\System.Security.Cryptography.Xml.4.5.0\lib\net461\System.Security.Cryptography.Xml.dll</HintPath>
+    </Reference>
+    <Reference Include="System.Security.Permissions, Version=4.0.1.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\System.Security.Permissions.4.5.0\lib\net461\System.Security.Permissions.dll</HintPath>
+    </Reference>
+    <Reference Include="System.Security.Principal.Windows, Version=4.1.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\System.Security.Principal.Windows.4.5.0\lib\net461\System.Security.Principal.Windows.dll</HintPath>
+    </Reference>
+    <Reference Include="System.ServiceProcess" />
+    <Reference Include="System.Transactions" />
     <Reference Include="System.Xml.Linq" />
     <Reference Include="System.Data.DataSetExtensions" />
     <Reference Include="System.Data" />
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="Cryptography\CryptographyHelpers.cs" />
     <Compile Include="FileAndStream\FileExample.cs" />
     <Compile Include="GlobalSuppressions.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
@@ -82,6 +101,7 @@
   <ItemGroup>
     <None Include="FileAndStream\README.md" />
     <None Include="Key.snk" />
+    <None Include="packages.config" />
     <None Include="Reflection\README.MD" />
   </ItemGroup>
   <ItemGroup>
@@ -96,9 +116,7 @@
       <Install>true</Install>
     </BootstrapperPackage>
   </ItemGroup>
-  <ItemGroup>
-    <Folder Include="Cryptography\" />
-  </ItemGroup>
+  <ItemGroup />
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.
diff --git a/Lecture/P03.DataStreams/DataStreams/packages.config b/Lecture/P03.DataStreams/DataStreams/packages.config
new file mode 100644
index 00000000..56708861
--- /dev/null
+++ b/Lecture/P03.DataStreams/DataStreams/packages.config
@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<packages>
+  <package id="System.Security.AccessControl" version="4.5.0" targetFramework="net471" />
+  <package id="System.Security.Cryptography.Xml" version="4.5.0" targetFramework="net471" />
+  <package id="System.Security.Permissions" version="4.5.0" targetFramework="net471" />
+  <package id="System.Security.Principal.Windows" version="4.5.0" targetFramework="net471" />
+</packages>
\ No newline at end of file