加密解密字符串

    /// <summary>
    /// 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
    /// </summary>
    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;

        }
    }