加密解密帮助类（对称加密）

  // 对称加密帮助类
    public static class CryptoHelper
    {
        //详细参考http://www.cnblogs.com/JimmyZhang/archive/2008/10/02/Cryptograph.html
        private static ICryptoTransform encryptor;     // 加密器对象
        private static ICryptoTransform decryptor;     // 解密器对象

        private static SymmetricAlgorithm provider = SymmetricAlgorithm.Create("TripleDES");

        private const int BufferSize = 1024;


        /// <summary>
        /// 加密算法
        /// </summary>
        /// <param name="key">为24或16位字符</param>
        /// <param name="encryptText">被加密的字符串</param>
        /// <returns></returns>
        public static string Encrypt(string key, string encryptedText)
        {
            provider.IV = new byte[] { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };
            provider.Key = Encoding.UTF8.GetBytes(key);

            encryptor = provider.CreateEncryptor();
            // 创建明文流
            byte[] clearBuffer = Encoding.UTF8.GetBytes(encryptedText);
            MemoryStream clearStream = new MemoryStream(clearBuffer);

            // 创建空的密文流
            MemoryStream encryptedStream = new MemoryStream();

            CryptoStream cryptoStream =
                new CryptoStream(encryptedStream, encryptor, CryptoStreamMode.Write);

            // 将明文流写入到buffer中
            // 将buffer中的数据写入到cryptoStream中
            int bytesRead = 0;
            byte[] buffer = new byte[BufferSize];
            do
            {
                bytesRead = clearStream.Read(buffer, 0, BufferSize);
                cryptoStream.Write(buffer, 0, bytesRead);
            } while (bytesRead > 0);

            cryptoStream.FlushFinalBlock();

            // 获取加密后的文本
            buffer = encryptedStream.ToArray();
            string str = Convert.ToBase64String(buffer);
            return str;
        }

        // 解密算法
        /// <summary>
        /// </summary>
        /// <param name="key">为24或16位字符</param>
        /// <param name="decryptedText">被解密的字符串</param>
        /// <returns></returns>
        public static string Decrypt(string key, string decryptedText)
        {
            provider.IV = new byte[] { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };
            provider.Key = Encoding.UTF8.GetBytes(key);

            decryptor = provider.CreateDecryptor();
            byte[] encryptedBuffer = Convert.FromBase64String(decryptedText);
            Stream encryptedStream = new MemoryStream(encryptedBuffer);

            MemoryStream clearStream = new MemoryStream();
            CryptoStream cryptoStream =
                new CryptoStream(encryptedStream, decryptor, CryptoStreamMode.Read);

            int bytesRead = 0;
            byte[] buffer = new byte[BufferSize];

            do
            {
                bytesRead = cryptoStream.Read(buffer, 0, BufferSize);
                clearStream.Write(buffer, 0, bytesRead);
            } while (bytesRead > 0);

            buffer = clearStream.GetBuffer();
            string str =
                Encoding.UTF8.GetString(buffer, 0, (int)clearStream.Length);

            return str;
        }

    }