using System;

using System.IO;

using System.Security.Cryptography;

using System.Text;

namespace Common

{

    /// <summary>

    /// 采用 3DES 加解密方式。

    /// </summary>

    public class EncryptAndDecrypte

    {

        static string strKey = "fdbc4y6hdhKlf4M3mjgGrMC3PbryXrxw";

        static string strIV = "RfnMfrpec48=";

        /// <summary>

        /// 默认加密字符串。

        /// </summary>

        /// <param name="ConnString"></param>

        /// <returns></returns>

        public static string EncryptString(string encryptString)

        {

            if (string.IsNullOrWhiteSpace(encryptString)) return encryptString;

            return Convert.ToBase64String(EncryptAndDecrypte.EncryptString(

                encryptString,

                Convert.FromBase64String(strKey),

                Convert.FromBase64String(strIV)

            )

            );

        }

        /// <summary>

        /// 默认解密字符串

        /// </summary>

        /// <param name="EncryptedConnectionString"></param>

        /// <returns></returns>

        public static string DecrypteString(string EncryptedConnectionString)

        {

            if (string.IsNullOrWhiteSpace(EncryptedConnectionString)) return EncryptedConnectionString;

            return EncryptAndDecrypte.DecrypteString(

                Convert.FromBase64String(EncryptedConnectionString),

                 Convert.FromBase64String(strKey),

                Convert.FromBase64String(strIV)

            ).TrimEnd('\0');

        }

        /// <summary>

        /// 使用指定的 Key 和 IV 加密 。

        /// </summary>

        /// <param name="ToEncryptString"></param>

        /// <param name="byKey"></param>

        /// <param name="byIV"></param>

        /// <returns></returns>

        private static byte[] EncryptString(string ToEncryptString, byte[] byKey, byte[] byIV)

        {

            if (string.IsNullOrWhiteSpace(ToEncryptString)) return null;

            MemoryStream memStm = new MemoryStream();

            TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider();

            CryptoStream encStream = null;

            encStream = new CryptoStream(

               memStm, tdes.CreateEncryptor(byKey, byIV), CryptoStreamMode.Write

               );

            byte[] byIn = Encoding.Default.GetBytes(ToEncryptString);

            encStream.Write(byIn, , byIn.Length);

            encStream.FlushFinalBlock();

            encStream.Close();

            return memStm.ToArray();

        }

        /// <summary>

        /// 使用指定的 Key 和 IV 解密。

        /// </summary>

        /// <param name="byIn"></param>

        /// <param name="byKey"></param>

        /// <param name="byIV"></param>

        /// <returns></returns>

        private static string DecrypteString(byte[] byIn, byte[] byKey, byte[] byIV)

        {

            if (byIn == null || byIn.Length == ) return string.Empty;

            MemoryStream memStm = new MemoryStream(byIn);

            TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider();

            CryptoStream encStream = new CryptoStream(

               memStm, tdes.CreateDecryptor(byKey, byIV), CryptoStreamMode.Read

               );

            byte[] fromEncrypt = new byte[byIn.Length];

            encStream.Read(fromEncrypt, , fromEncrypt.Length);

            encStream.Close();

            string strRet = Encoding.Default.GetString(fromEncrypt);

            return strRet;

        }

        /// <summary>

        /// 获取随机（种子是 GUID 的 Byte 的和）长度的Byte数组.

        /// </summary>

        /// <param name="Len">要得到的数组的长度</param>

        /// <returns></returns>

        private static byte[] GetBytes(int Len)

        {

            int Seed = ;

            byte[] bySeed = Guid.NewGuid().ToByteArray();

            foreach (byte byt in bySeed)

            {

                Seed += byt;

            }

            byte[] byKey = new byte[Len];

            new Random(Seed).NextBytes(byKey);

            return byKey;

        }

        /// <summary>

        /// 获取 Key 和 IV ， 如果失败，返回null。

        /// </summary>

        /// <param name="Key"></param>

        /// <param name="IV"></param>

        public static void TryGetKeyAndIV(out byte[] Key, out byte[] IV)

        {

            TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider();

            for (int i = ; i > ; i--)

            {

                try

                {

                    Key = GetBytes(i);

                    IV = GetBytes(i);

                    tdes.CreateDecryptor(Key, IV);

                    return;

                }

                catch

                {

                }

            }

            Key = null;

            IV = null;

            return;

        }

    }

}