/// 
 /// 基于 ProtectedData 实现的加密解密字符串，可以跨windows用户使用，但是不能跨计算机使用 /// 
     public static class EncryptHelper     {
   public static string Encrypt(string stringToEncrypt)         {
   byte[] toEncrypt = UnicodeEncoding.UTF8.GetBytes(stringToEncrypt);             MemoryStream stream = new MemoryStream(); int bytesWritten = EncryptDataToStream(toEncrypt, null, DataProtectionScope.LocalMachine, stream);             stream.Close(); return Convert.ToBase64String(stream.ToArray());         } public static string Decrypt(string encryptedString)         {
   byte[] encrypted = Convert.FromBase64String(encryptedString);             MemoryStream stream = new MemoryStream(encrypted); byte[] decryptData = DecryptDataFromStream(null, DataProtectionScope.LocalMachine, stream, encrypted.Length);             stream.Close(); return UnicodeEncoding.UTF8.GetString(decryptData);         } private static int EncryptDataToStream(byte[] buffer, byte[] entropy, DataProtectionScope scope, Stream stream)         {
   if (buffer == null)             {
   throw new ArgumentNullException("buffer");             } if (buffer.Length <= 0)             {
   throw new ArgumentException("buffer");             } if (stream == null)             {
   throw new ArgumentNullException("stream");             } int length = 0; byte[] encrptedData = ProtectedData.Protect(buffer, entropy, scope); if (stream.CanWrite && encrptedData != null)             {
                   stream.Write(encrptedData, 0, encrptedData.Length);                 length = encrptedData.Length;             } return length;         } private static byte[] DecryptDataFromStream(byte[] entropy, DataProtectionScope scope, Stream stream, int length)         {
   if (stream == null)             {
   throw new ArgumentNullException("stream");             } if (length <= 0)             {
   throw new ArgumentException("length");             } byte[] inBuffer = new byte[length]; byte[] outBuffer; if (stream.CanRead)             {
                   stream.Read(inBuffer, 0, length);                 outBuffer = ProtectedData.Unprotect(inBuffer, entropy, scope);             } else             {
   throw new IOException("Could not read the stream.");             } return outBuffer;         }     }