C# 加密和解密文件

相关示例代码如下：

 using System;
 using System.IO;
 using System.Security;
 using System.Security.Cryptography;
 using System.Runtime.InteropServices;
 using System.Text;

 namespace CSEncryptDecrypt
 {
    class Class1
    {
       //  Call this function to remove the key from memory after use for security
       [System.Runtime.InteropServices.DllImport("KERNEL32.DLL", EntryPoint="RtlZeroMemory")]
       public static extern bool ZeroMemory(IntPtr Destination, int Length);

       // Function to Generate a 64 bits Key.
       static string GenerateKey()
       {
          // Create an instance of Symetric Algorithm. Key and IV is generated automatically.
          DESCryptoServiceProvider desCrypto =(DESCryptoServiceProvider)DESCryptoServiceProvider.Create();

          // Use the Automatically generated key for Encryption.
          return ASCIIEncoding.ASCII.GetString(desCrypto.Key);
       }

       static void EncryptFile(string sInputFilename,
          string sOutputFilename,
          string sKey)
       {
          FileStream fsInput = new FileStream(sInputFilename,
             FileMode.Open,
             FileAccess.Read);

          FileStream fsEncrypted = new FileStream(sOutputFilename,
             FileMode.Create,
             FileAccess.Write);
          DESCryptoServiceProvider DES = new DESCryptoServiceProvider();
          DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);
          DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);
          ICryptoTransform desencrypt = DES.CreateEncryptor();
          CryptoStream cryptostream = new CryptoStream(fsEncrypted,
             desencrypt,
             CryptoStreamMode.Write); 

          byte[] bytearrayinput = new byte[fsInput.Length];
          fsInput.Read(bytearrayinput, , bytearrayinput.Length);
          cryptostream.Write(bytearrayinput, , bytearrayinput.Length);
          cryptostream.Close();
          fsInput.Close();
          fsEncrypted.Close();
       }

       static void DecryptFile(string sInputFilename,
          string sOutputFilename,
          string sKey)
       {
          DESCryptoServiceProvider DES = new DESCryptoServiceProvider();
          //A 64 bit key and IV is 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.
          FileStream fsread = new FileStream(sInputFilename,
             FileMode.Open,
             FileAccess.Read);
          //Create a DES decryptor from the DES instance.
          ICryptoTransform desdecrypt = DES.CreateDecryptor();
          //Create crypto stream set to read and do a
          //DES decryption transform on incoming bytes.
          CryptoStream cryptostreamDecr = new CryptoStream(fsread,
             desdecrypt,
             CryptoStreamMode.Read);
          //Print the contents of the decrypted file.
          StreamWriter fsDecrypted = new StreamWriter(sOutputFilename);
          fsDecrypted.Write(new StreamReader(cryptostreamDecr).ReadToEnd());
          fsDecrypted.Flush();
          fsDecrypted.Close();
       } 

       static void Main()
       {
          // Must be 64 bits, 8 bytes.
          // Distribute this key to the user who will decrypt this file.
          string sSecretKey;

          // Get the Key for the file to Encrypt.
          sSecretKey = GenerateKey();

          // For additional security Pin the key.
          GCHandle gch = GCHandle.Alloc( sSecretKey,GCHandleType.Pinned );

          // Encrypt the file.
          EncryptFile(@"C:\MyData.txt",
             @"C:\Encrypted.txt",
             sSecretKey);

          // Decrypt the file.
          DecryptFile(@"C:\Encrypted.txt",
             @"C:\Decrypted.txt",
             sSecretKey);

          // Remove the Key from memory.
          ZeroMemory(gch.AddrOfPinnedObject(), sSecretKey.Length * );
          gch.Free();
       }
    }
 }