using System;
using System.Text;
using System.IO;
namespace 加密解密 
{


	///<summary>
	/// Base64編碼/解碼類，提供標準Base64編碼和解碼，靜態類，不能創建實例。
	/// </summary>
	public static class Base64 
    {

		/// <summary>
		/// 編碼方法，靜態方法。
        /// 使用方法：
        ///    string Message = "";//需要編碼的字符串
        ///    string DestString = Base64.Encrypt(Message);
		/// </summary>
		/// <param name="Message">需要進行編碼的字符串，支持中文</param>
		/// <returns>字符串，如果處理出現錯誤，則返回0長度的字符串</returns>
        public static string Encrypt( string Message )
        {

            char[] Base64Code = mBase64key.ToCharArray();

            byte empty = (byte)0;
            System.Collections.ArrayList byteMessage = new System.Collections.ArrayList(System.Text.Encoding.Default.GetBytes(Message));
            System.Text.StringBuilder outmessage;
            int messageLen = byteMessage.Count;
            int page = messageLen / 3;
            int use = 0;
            if ((use = messageLen % 3) > 0)
            {
                for (int i = 0; i < 3 - use; i++)
                    byteMessage.Add(empty);
                page++;
            }
            outmessage = new System.Text.StringBuilder(page * 4);
            for (int i = 0; i < page; i++)
            {
                byte[] instr = new byte[3];
                instr[0] = (byte)byteMessage[i * 3];
                instr[1] = (byte)byteMessage[i * 3 + 1];
                instr[2] = (byte)byteMessage[i * 3 + 2];
                int[] outstr = new int[4];
                outstr[0] = instr[0] >> 2;
                outstr[1] = ((instr[0] & 0x03) << 4) ^ (instr[1] >> 4);
                if (!instr[1].Equals(empty))
                    outstr[2] = ((instr[1] & 0x0f) << 2) ^ (instr[2] >> 6);
                else
                    outstr[2] = 64;
                if (!instr[2].Equals(empty))
                    outstr[3] = (instr[2] & 0x3f);
                else
                    outstr[3] = 64;
                outmessage.Append(Base64Code[outstr[0]]);
                outmessage.Append(Base64Code[outstr[1]]);
                outmessage.Append(Base64Code[outstr[2]]);
                outmessage.Append(Base64Code[outstr[3]]);
            }
            return outmessage.ToString();
        }
		/// <summary>
		/// 解碼方法，靜態方法
        /// 使用方法：
        ///    string Message = "";//需要解碼的字符串
        ///    string DestString = Base64.Decrypt(Message);
		/// </summary>
		/// <param name="Message">需要進行解碼的字符串</param>
		/// <returns>解碼后的字符串，如果處理出現錯誤，則返回0長度的字符串</returns>
        public static string Decrypt( string Message )
        {
            if ((Message.Length % 4) != 0)
            {
                return "";
                //throw new ArgumentException("不是正確的BASE64編碼，請檢查。", "Message");
            }
            if (!System.Text.RegularExpressions.Regex.IsMatch(Message, "^[A-Z0-9/+=]*$", System.Text.RegularExpressions.RegexOptions.IgnoreCase))
            {
                return "";
                //throw new ArgumentException("包含不正確的BASE64編碼，請檢查。", "Message");
            }
            //string Base64Code="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
            string Base64Code = mBase64key;

            int page = Message.Length / 4;
            System.Collections.ArrayList outMessage = new System.Collections.ArrayList(page * 3);
            char[] message = Message.ToCharArray();
            for (int i = 0; i < page; i++)
            {
                byte[] instr = new byte[4];
                instr[0] = (byte)Base64Code.IndexOf(message[i * 4]);
                instr[1] = (byte)Base64Code.IndexOf(message[i * 4 + 1]);
                instr[2] = (byte)Base64Code.IndexOf(message[i * 4 + 2]);
                instr[3] = (byte)Base64Code.IndexOf(message[i * 4 + 3]);
                byte[] outstr = new byte[3];
                outstr[0] = (byte)((instr[0] << 2) ^ ((instr[1] & 0x30) >> 4));
                if (instr[2] != 64)
                {
                    outstr[1] = (byte)((instr[1] << 4) ^ ((instr[2] & 0x3c) >> 2));
                }
                else
                {
                    outstr[2] = 0;
                }
                if (instr[3] != 64)
                {
                    outstr[2] = (byte)((instr[2] << 6) ^ instr[3]);
                }
                else
                {
                    outstr[2] = 0;
                }
                outMessage.Add(outstr[0]);
                if (outstr[1] != 0)
                    outMessage.Add(outstr[1]);
                if (outstr[2] != 0)
                    outMessage.Add(outstr[2]);
            }
            byte[] outbyte = (byte[])outMessage.ToArray(Type.GetType("System.Byte"));
            return System.Text.Encoding.Default.GetString(outbyte);
        }

		/// <summary>
		/// 如果需要更換密鑰，替換以下字符串即可
		/// </summary>
        //private static  string mBase64key = "jEmudAnDU7GKtb018q6ZkrBV+/acThPQ45geO2xyHisvzlYpIRNwCSWXJFf93oLM=";
        private static string mBase64key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
	}
}