/// <summary>
///Base64 编码/解码
/// </summary>
public class Base64
{
    /// <summary>
    /// Base64编码
    /// </summary>
    /// <param name="Message"></param>
    /// <returns></returns>
    public static string Base64Encode(string Message)
    {
        char[] Base64Code = new char[]{'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T',
         'U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n',
         'o','p','q','r','s','t','u','v','w','x','y','z','0','1','2','3','4','5','6','7',
         '8','9','+','/','='};
        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>
    /// Base64解码
    /// </summary>
    /// <param name="Message"></param>
    /// <returns></returns>
    public static string Base64Decode(string Message)
    {
        if ((Message.Length % 4) != 0)
        {
            throw new ArgumentException("不是正确的BASE64编码，请检查。", "Message");
        }
        if (!System.Text.RegularExpressions.Regex.IsMatch(Message, "^[A-Z0-9/+=]*$", System.Text.RegularExpressions.RegexOptions.IgnoreCase))
        {
            throw new ArgumentException("包含不正确的BASE64编码，请检查。", "Message");
        }
        string Base64Code = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
        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);
    }
}