我想對資料庫的某一欄位加密, 但必須是可回復的加密 查了以往的文章: http://delphi.ktop.com.tw/topic.php?topic_id=56059 shieh2700 先生提到, 可以用 DES(對稱式加密) 或 RSA(非對稱式加密) 等演算法, 請問DES或RSA 如何使用呢? 或者有沒有其他可回復的加解密方法?

下述範例節錄自: http://msdn.microsoft.com/library/cht/default.asp?url=/library/CHT/cpref/html/frlrfsystemsecuritycryptographydesclasstopic.php    範例 [Visual Basic, C#, C++] 以下範例方法使用 DESCryptoServiceProvider (DES 的實作) 配合指定的 Key 和初始化向量 (IV)，加密由 inName 指定的檔案，並且將加密的結果輸出至 outName 所指定的檔案。

[Visual Basic] 
Private Shared Sub EncryptData(inName As String, outName As String, _
desKey() As Byte, desIV() As Byte)        'Create the file streams to handle the input and output files.
    Dim fin As New FileStream(inName, FileMode.Open, FileAccess.Read)
    Dim fout As New FileStream(outName, FileMode.OpenOrCreate, _
       FileAccess.Write)
    fout.SetLength(0)
    
    'Create variables to help with read and write.
    Dim bin(4096) As Byte 'This is intermediate storage for the encryption.
    Dim rdlen As Long = 0 'This is the total number of bytes written.
    Dim totlen As Long = fin.Length 'Total length of the input file.
    Dim len As Integer 'This is the number of bytes to be written at a time.
    Dim des As New DESCryptoServiceProvider()
    Dim encStream As New CryptoStream(fout, _
       des.CreateEncryptor(desKey, desIV), CryptoStreamMode.Write)
    
    Console.WriteLine("Encrypting...")
    
    'Read from the input file, then encrypt and write to the output file.
    While rdlen < totlen
        len = fin.Read(bin, 0, 4096)
        encStream.Write(bin, 0, len)
        rdlen = Convert.ToInt32(rdlen   len / des.BlockSize * des.BlockSize)
        Console.WriteLine("Processed {0} bytes, {1} bytes total", len, _
           rdlen)
    End While
    
    encStream.Close()
End Sub    [C#] 
private static void EncryptData(String inName, String outName, byte[] desKey, byte[] desIV)
 {    
     //Create the file streams to handle the input and output files.
     FileStream fin = new FileStream(inName, FileMode.Open, FileAccess.Read);
     FileStream fout = new FileStream(outName, FileMode.OpenOrCreate, FileAccess.Write);
     fout.SetLength(0);
       
     //Create variables to help with read and write.
     byte[] bin = new byte[100]; //This is intermediate storage for the encryption.
     long rdlen = 0;              //This is the total number of bytes written.
     long totlen = fin.Length;    //This is the total length of the input file.
     int len;                     //This is the number of bytes to be written at a time.
 
     DES des = new DESCryptoServiceProvider();          
     CryptoStream encStream = new CryptoStream(fout, des.CreateEncryptor(desKey, desIV), CryptoStreamMode.Write);
                
     Console.WriteLine("Encrypting...");
 
     //Read from the input file, then encrypt and write to the output file.
     while(rdlen < totlen)
     {
         len = fin.Read(bin, 0, 100);
         encStream.Write(bin, 0, len);
         rdlen = rdlen   len;
         Console.WriteLine("{0} bytes processed", rdlen);
     }
 
     encStream.Close();  
     fout.Close();
     fin.Close();                   
 }

[Visual Basic, C#] 解密可用相同的方式處理，即使用 CreateDecryptor ，而非 CreateEncryptor 。用來加密檔案的 Key 和 IV 必須與解密檔案的相同。