MSDN上的一个不错的例子： 那从内存清除密码的句子有个问题。 需要再看看这个问题到底是怎么回事，怎么解决

cannot convert from Sytem.InPtr to ref string

把下面这句

public static extern bool ZeroMemory(ref string Destination, int Length);

用这句替换就OK了

internal static extern void ZeroMemory(IntPtr handle, int length);

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Security;
using System.Security.Cryptography;
using System.Runtime.InteropServices;namespace MSDNEncryExample
{class Program{//  Call this function to remove the key from memory after use for security.[System.Runtime.InteropServices.DllImport("KERNEL32.DLL", EntryPoint = "RtlZeroMemory")]internal static extern void ZeroMemory(IntPtr handle, 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){// Create a file stream to read the data to be encryptedFileStream fsInput = new FileStream(sInputFilename,FileMode.Open,FileAccess.Read);//Crete a file stream for the encrypted dataFileStream fsEncrypted = new FileStream(sOutputFilename,FileMode.Create,FileAccess.Write);// Create encryptor by usin the keyDESCryptoServiceProvider DES = new DESCryptoServiceProvider();DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);ICryptoTransform desencrypt = DES.CreateEncryptor();// Create a CrytoStream to link the encrypted stream and the encryptorCryptoStream cryptostream = new CryptoStream(fsEncrypted,desencrypt,CryptoStreamMode.Write);// Read the file stream to bytes arraybyte[] bytearrayinput = new byte[fsInput.Length];fsInput.Read(bytearrayinput, 0, bytearrayinput.Length);// Encrypt the byte array by using the CryptoStreamcryptostream.Write(bytearrayinput,0,bytearrayinput.Length);// Close the file streamscryptostream.Close();fsInput.Close();fsEncrypted.Close();}static void DecryptFile(string sInputFilename,string sOutputFilename,string sKey){// Set the DESCryptoServiceProvider classDESCryptoServiceProvider 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(string[] args){// 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 * 2);gch.Free();}}
}

另外一个例子

using System;
using System.Security.Cryptography;
using System.Text;
using System.IO;class RijndaelSample
{static void Main(){try{// Create a new Rijndael object to generate a key// and initialization vector (IV).Rijndael RijndaelAlg = Rijndael.Create();// Create a string to encrypt.string sData = "Here is some data to encrypt.";string FileName = "CText.txt";// Encrypt text to a file using the file name, key, and IV.EncryptTextToFile(sData, FileName, RijndaelAlg.Key, RijndaelAlg.IV);// Decrypt the text from a file using the file name, key, and IV.string Final = DecryptTextFromFile(FileName, RijndaelAlg.Key, RijndaelAlg.IV);// Display the decrypted string to the console.Console.WriteLine(Final);}catch (Exception e){Console.WriteLine(e.Message);}Console.ReadLine();}public static void EncryptTextToFile(String Data, String FileName, byte[] Key, byte[] IV){try{// Create or open the specified file.FileStream fStream = File.Open(FileName, FileMode.OpenOrCreate);// Create a new Rijndael object.Rijndael RijndaelAlg = Rijndael.Create();// Create a CryptoStream using the FileStream // and the passed key and initialization vector (IV).CryptoStream cStream = new CryptoStream(fStream,RijndaelAlg.CreateEncryptor(Key, IV),CryptoStreamMode.Write);// Create a StreamWriter using the CryptoStream.StreamWriter sWriter = new StreamWriter(cStream);try{// Write the data to the stream // to encrypt it.sWriter.WriteLine(Data);}catch (Exception e){Console.WriteLine("An error occurred: {0}", e.Message);}finally{// Close the streams and// close the file.sWriter.Close();cStream.Close();fStream.Close();}}catch (CryptographicException e){Console.WriteLine("A Cryptographic error occurred: {0}", e.Message);}catch (UnauthorizedAccessException e){Console.WriteLine("A file error occurred: {0}", e.Message);}}public static string DecryptTextFromFile(String FileName, byte[] Key, byte[] IV){try{// Create or open the specified file. FileStream fStream = File.Open(FileName, FileMode.OpenOrCreate);// Create a new Rijndael object.Rijndael RijndaelAlg = Rijndael.Create();// Create a CryptoStream using the FileStream // and the passed key and initialization vector (IV).CryptoStream cStream = new CryptoStream(fStream,RijndaelAlg.CreateDecryptor(Key, IV),CryptoStreamMode.Read);// Create a StreamReader using the CryptoStream.StreamReader sReader = new StreamReader(cStream);string val = null;try{// Read the data from the stream // to decrypt it.val = sReader.ReadLine();}catch (Exception e){Console.WriteLine("An error occurred: {0}", e.Message);}finally{// Close the streams and// close the file.sReader.Close();cStream.Close();fStream.Close();}// Return the string. return val;}catch (CryptographicException e){Console.WriteLine("A Cryptographic error occurred: {0}", e.Message);return null;}catch (UnauthorizedAccessException e){Console.WriteLine("A file error occurred: {0}", e.Message);return null;}}
}

这个