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��Ѻ�� Microsoft Visual c# .NET �ͧ�� 307010

(http://support.microsoft.com/kb/307010/EN-US/ )

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Microsoft Windows XP, Microsoft Windows Server 2003, Microsoft Windows 2000 Professional, Microsoft Windows 2000 Server, Microsoft Windows 2000 Server ��â��٧ ��ͧ Microsoft Windows NT 4.0
Microsoft Visual Studio .NET �� Microsoft Visual Studio 2005

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namespace System.Security.Cryptographic �.NET Framework �ʴ��ҧ � �ͧ��ͧ��ͷ�� 㹡�� жʹ��Ѻ ��кǹ��CryptoStream��ʷ��դ��ʷ��ӹǹ�ҡ��ҧ��ҧ˹�� кǹ��CryptoStream��͡Ẻ�� Ѻ ��Ͷʹ��Ѻ�� ҷ��ѧʵ��͡��ѧ��

��Ѻ�� Թ��ôѧ��仹��:

��¡�� Visual Studio .NET �� Visual Studio 2005
��ҧ��ء��͹�� Visual Basic .NET �� Visual Basic 2005 ��ҧ��ŷ��س ��Ѻ��ҧ��Main()��鹵͹
��Ẻ����ʹ� namespace �к� System.Security namespace, System.Security.Cryptography namespace, System.Text namespace �� System.IO namespace �س��ͧ��蹹��س��ա�á�˹��س��ѵ� declarations �ҡ namespaces ��ҹ��ѧ��ʢͧ�س �س��ͧ��ҹ��͹�� declarations ��
Imports System Imports System.IO Imports System.Security Imports System.Security.Cryptography Imports System.Runtime.InteropServices Imports System.Text
��ҧ��Ѻ� �� жʹ��ʢ�� кǹ��DESCryptoServiceProvider��ʷ��Т��Ѻ��š��Է��Ѻ symmetric ��Ѻ symmetric ��ͧ�դ�� vector ��ҹ (IV) 㹡��ʢ�� ͵�ͧ��öʹ��ʢ�� س��ͧ�դ��ǡѹ�� IV ��͹�ѹ �͡�ҡ��س��ͧ��š��Է��Ѻ��ǡѹ �س��ö��ҧ�� Ըա�õ��仹��:
- �Ըշ�� 1:�س��ö�ʴ��ͧ��ͺ��ʼ�ҹ ��ʼ�ҹ�� 繤�� IV
- �Ըշ�� 2��ͤس��ҧ�Թ�ᵹ��ͧ��ʢͧ��Ѻ symmetric �� IV ��١��ҧ��ѵ��ѵ��Ѻ�ʪѹ �س��ö�� IV ��ҧ�� Ѻ��èѴ�� symmetric ��Ѻ�� жʹ��Ѻ��
  
  ��Ѻ��ǡѺ�Ը� ��ҧ �� á�Ш�¤�� 䫵��仹��ͧ Microsoft ��ʹ��͡��êش (SDK) �ͧ��þѲ�ҫͿ��.NET Framework:
  
  .aspx http://msdn.microsoft.com/en-us/library/5e9ft273 (VS.71)
  (http://msdn.microsoft.com/en-us/library/5e9ft273(VS.71).aspx)

��ѧ��ѹ��仹��ҧ��Ѻ�ʪѹ㹢�з��ѹ�֡��Ըշ�� 2:

   ' Call this function to remove the key from memory after it is used for security.
   Private Declare Sub ZeroMemory Lib "kernel32.dll" Alias "RtlZeroMemory" _
                     (ByVal Destination As String, ByVal Length As Integer)
   
   ' Function to generate a key.
   Function GenerateKey() As String
      ' Create an instance of Symmetric Algorithm. The key and the IV are generated automatically.
      Dim desCrypto As DESCryptoServiceProvider = DESCryptoServiceProvider.Create()

      ' Use the automatically generated key for encryption. 
      Return ASCIIEncoding.ASCII.GetString(desCrypto.Key)
   End Function

��ҧ�Ըա��㹤�ҷ��EncryptFile. ��кǹ��EncryptFile�Ըյ�ͧ�վ��:
- sInputFile
- sOutputFile
- sKey(��ͤ��Ѻ�� жʹ��Ѻ��)
Sub EncryptFile(ByVal sInputFilename As String, _ ByVal sOutputFilename As String, _ ByVal sKey As String) End Sub

㹡��EncryptFile��кǹ�� ҧ��û�͹��FileStream�ѵ��С��ʴ��FileStream�ѵ�� ѵ��ҹ��ö��ҹ�ҡ ��¹��ѧ��

        Dim fsInput As New FileStream(sInputFilename, _
                                    FileMode.Open, FileAccess.Read)
        Dim fsEncrypted As New FileStream(sOutputFilename, _
                                    FileMode.Create, FileAccess.Write)

�Թ�ᵹ��ͧ��û�С��DESCryptoServiceProvider��ʷ�� ʴ��֧෤��ա�öʹ��Ѻ��ԧ��麹��С��Ѻ��ԧ ��ش�� س��ö��ҧ��ԡ��Ҥس��ͧ��ѡ�Ҥ��ʹ�� RSA ��෤�Ԥ��Ѻ��
Dim DES As New DESCryptoServiceProvider()
��ԡ�á��Ѻ��ͧ��ö��Ѻ��Ѻ�ͧ�س��亵� System.Text namespace �տѧ��ѹ��ժ��GetBytes(). ��ǹ˹�觢ͧ�س�ѡɳС�� GetBytes()�ѧ��ѹ��ʵ�ԧ�� ͧ亵��觡�Ѻ�� Ҵ�ͧ��ᵡ��ҧ�ѹ��Ѻ��෤�Ԥ˹�觷��㹡��Ѻ�� ҧ�� š��Ѻ�ҵðҹ (DES) ��Ẻ 64 �Ե�� Ѻ 8 亵� �� 8 ��

��Ҥس��դ�� ҡ��ԡ��Ẻ��ҧ˹�� º�� Ըա�öʹ��Ѻ�� ô�ѧࡵ�� س�е�ͧ�� IV �� ҹ��ǹ˹�觢ͧ��Ѻ ��ǡѺ�� IV �ա��ҧ��Ҥس�� ͧ�ҡ��ҵ�ͧ��͹�ѹ��Ѻ��Ѻ��С�öʹ��Ѻ �س��ͧ��͹حҵ��ҧ��ҹ��Ẻ��
DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey) DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey)
��ҧ�Թ�ᵹ��ͧ��CryptoStream��ʷ�� ԡ�á��Ѻ��͢��Ѻ��(encrypting �ͧ�ѵ��CreateEncryptor) ��мż�Ե��FileStreamobject as a part of the constructor.
Dim cryptostream As New CryptoStream(fsEncrypted, _ desencrypt, _ CryptoStreamMode.Write)

Read in the input file, and then write out to the output file. Pass through theCryptoStreamobject where the file is encrypted by using the key that you provided.

Dim bytearrayinput(fsInput.Length - 1) As Byte
fsInput.Read(bytearrayinput, 0, bytearrayinput.Length)
cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length)

To decrypt a file, follow these steps:

Create a method that is namedDecryptFile. The decryption process is similar to the encryption process. However,DecryptFilehas two key differences from theEncryptFile��鹵͹

CreateDecryptoris used instead ofCreateEncryptor��͵�ͧ��ҧ��CryptoStreamobject that specifies how the object can be used.
When the decrypted text is written to the destination file, theCryptoStreamobject is now the source instead of the destination stream.

Sub DecryptFile(ByVal sInputFilename As String, _
    ByVal sOutputFilename As String, _
    ByVal sKey As String)

    Dim DES As New DESCryptoServiceProvider()
    'A 64-bit key and an IV are required for this provider.
    'Set secret key for DES algorithm.
    DES.Key() = ASCIIEncoding.ASCII.GetBytes(sKey)
    'Set initialization vector.
    DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey)

    'Create a file stream to read the encrypted file back.
    Dim fsread As New FileStream(sInputFilename, FileMode.Open, FileAccess.Read)
    'Create a DES Decryptor from your DES instance.
    Dim desdecrypt As ICryptoTransform = DES.CreateDecryptor()
    'Create a crypto stream set to read and to do a DES decryption transform on incoming bytes.
    Dim cryptostreamDecr As New CryptoStream(fsread, desdecrypt, CryptoStreamMode.Read)
    'Print out the contents of the decrypted file.
    Dim fsDecrypted As New StreamWriter(sOutputFilename)
    fsDecrypted.Write(New StreamReader(cryptostreamDecr).ReadToEnd)
    fsDecrypted.Flush()
    fsDecrypted.Close()
End Sub

Add the following lines to theMain()procedure to call bothEncryptFile��DecryptFile.

    Public Sub Main()      'Must be 64 bits, 8 bytes.
      Dim sSecretKey As String

      ' Get the key for the file to encrypt.
      ' You can distribute this key to the user who will decrypt the file.
      sSecretKey = GenerateKey()

      ' For additional security, pin the key.
      Dim gch As GCHandle = GCHandle.Alloc(sSecretKey, GCHandleType.Pinned)


      ' Encrypt the file.        
      EncryptFile("%USERPROFILE%\MyData.txt", _
                      "%USERPROFILE%\Encrypted.txt", _
                      sSecretKey)

      ' Decrypt the file.
      DecryptFile("%USERPROFILE%\Encrypted.txt", _
                  "%USERPROFILE%\Decrypted.txt", _
                  sSecretKey)

      ' Remove the key from memory.
      ZeroMemory(gch.AddrOfPinnedObject(), sSecretKey.Length * 2)
      gch.Free()
   End Sub

�ѹ�֡�� Run your application. Make sure that the path that is used for the input file name points to an existing and a not important file.

Verify That the Encryption and the Decryption Work

Test this code with a text (.txt) file to confirm that the file is correctly encrypted and decrypted. Make sure that you decrypt the file to a new file (as in theSub Main()procedure in this article) instead of to the original file. Examine the decrypted file and compare the decrypted file to the original.

A Complete Code List

Imports System
Imports System.IO
Imports System.Security
Imports System.Security.Cryptography
Imports System.Runtime.InteropServices
Imports System.Text


Module Module1

   ' Call this function to remove the key from memory after it is used for security.
   <DllImport("kernel32.dll")> _
   Public Sub ZeroMemory(ByVal addr As IntPtr, ByVal size As Integer)
   End Sub

   ' Function to generate a 64-bit key.
   Function GenerateKey() As String
      ' Create an instance of a symmetric algorithm. The key and the IV are generated automatically.
      Dim desCrypto As DESCryptoServiceProvider = DESCryptoServiceProvider.Create()

      ' Use the automatically generated key for encryption. 
      Return ASCIIEncoding.ASCII.GetString(desCrypto.Key)

   End Function

   Sub EncryptFile(ByVal sInputFilename As String, _
                  ByVal sOutputFilename As String, _
                  ByVal sKey As String)

      Dim fsInput As New FileStream(sInputFilename, _
                                  FileMode.Open, FileAccess.Read)
      Dim fsEncrypted As New FileStream(sOutputFilename, _
                                  FileMode.Create, FileAccess.Write)

      Dim DES As New DESCryptoServiceProvider()

      'Set secret key for DES algorithm.
      'A 64-bit key and an IV are required for this provider.
      DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey)

      'Set the initialization vector.
      DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey)

      'Create the DES encryptor from this instance.
      Dim desencrypt As ICryptoTransform = DES.CreateEncryptor()
      'Create the crypto stream that transforms the file stream by using DES encryption.
      Dim cryptostream As New CryptoStream(fsEncrypted, _
                                          desencrypt, _
                                          CryptoStreamMode.Write)

      'Read the file text to the byte array.
      Dim bytearrayinput(fsInput.Length - 1) As Byte
      fsInput.Read(bytearrayinput, 0, bytearrayinput.Length)
      'Write out the DES encrypted file.
      cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length)
      cryptostream.Close()
   End Sub

   Sub DecryptFile(ByVal sInputFilename As String, _
       ByVal sOutputFilename As String, _
       ByVal sKey As String)

      Dim DES As New DESCryptoServiceProvider()
      'A 64-bit key and an IV are required for this provider.
      'Set the secret key for the DES algorithm.
      DES.Key() = ASCIIEncoding.ASCII.GetBytes(sKey)
      'Set the initialization vector.
      DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey)

      'Create the file stream to read the encrypted file back.
      Dim fsread As New FileStream(sInputFilename, FileMode.Open, FileAccess.Read)
      'Create the DES decryptor from the DES instance.
      Dim desdecrypt As ICryptoTransform = DES.CreateDecryptor()
      'Create the crypto stream set to read and to do a DES decryption transform on incoming bytes.
      Dim cryptostreamDecr As New CryptoStream(fsread, desdecrypt, CryptoStreamMode.Read)
      'Print out the contents of the decrypted file.
      Dim fsDecrypted As New StreamWriter(sOutputFilename)
      fsDecrypted.Write(New StreamReader(cryptostreamDecr).ReadToEnd)
      fsDecrypted.Flush()
      fsDecrypted.Close()
   End Sub

   Public Sub Main()
      'Must be 64 bits, 8 bytes.
      Dim sSecretKey As String

      ' Get the key for the file to encrypt.
      ' You can distribute this key to the user who will decrypt the file.
      sSecretKey = GenerateKey()

      ' For additional security, pin the key.
      Dim gch As GCHandle = GCHandle.Alloc(sSecretKey, GCHandleType.Pinned)


      ' Encrypt the file.        
      EncryptFile("%USERPROFILE%\MyData.txt", _
                      "%USERPROFILE%\Encrypted.txt", _
                      sSecretKey)

      ' Decrypt the file.
      DecryptFile("%USERPROFILE%\Encrypted.txt", _
                  "%USERPROFILE%\Decrypted.txt", _
                  sSecretKey)

      ' Remove the key from memory. 
      ZeroMemory(gch.AddrOfPinnedObject(), sSecretKey.Length * 2)
      gch.Free()
   End Sub

End Module

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For more information about how to use the cryptographic features of .NET and about cryptography, visit the following Microsoft Web sites:

http://msdn.microsoft.com/net

(http://msdn.microsoft.com/net)

http://code.msdn.microsoft.com/

(http://code.msdn.microsoft.com/)

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��Ţ�� (Article ID): 301070 - ��Ǥ��ش��: 10 ��Ҥ� 2554 - Revision: 3.0

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Microsoft Visual Basic 2005
Microsoft Visual Basic .NET 2003 Standard Edition
Microsoft Visual Basic .NET 2002 Standard Edition

kbvs2005swept kbvs2005applies kbsecurity kbio kbcrypt kbhowtomaster kbmt KB301070 KbMtth

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(http://support.microsoft.com/kb/301070/en-us/ )

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