using System;
using System.Security.Cryptography;
using System.Text;

public static class NetworkValideRc4Sdk
{
    static string Md5(string text)
    {
        using (var md5 = MD5.Create())
        {
            var bytes = md5.ComputeHash(Encoding.UTF8.GetBytes(text));
            return BitConverter.ToString(bytes).Replace("-", "").ToLowerInvariant();
        }
    }

    static byte[] Rc4(byte[] data, byte[] key)
    {
        var box = new int[256];
        for (int i = 0; i < 256; i++) box[i] = i;
        int j = 0;
        for (int i = 0; i < 256; i++)
        {
            j = (j + box[i] + key[i % key.Length]) & 255;
            var t = box[i]; box[i] = box[j]; box[j] = t;
        }
        var output = new byte[data.Length];
        int a = 0; j = 0;
        for (int i = 0; i < data.Length; i++)
        {
            a = (a + 1) & 255;
            j = (j + box[a]) & 255;
            var t = box[a]; box[a] = box[j]; box[j] = t;
            output[i] = (byte)(data[i] ^ box[(box[a] + box[j]) & 255]);
        }
        return output;
    }

    public static string Encode(string rawData, string rc4Key)
    {
        var key = Md5(rc4Key);
        var keya = Md5(key.Substring(0, 16));
        var keyb = Md5(key.Substring(16, 16));
        var keyc = Md5(DateTime.Now.Ticks.ToString()).Substring(28, 4);
        var cryptkey = Encoding.UTF8.GetBytes(keya + Md5(keya + keyc));
        var payload = Encoding.UTF8.GetBytes("0000000000" + Md5(rawData + keyb).Substring(0, 16) + rawData);
        return keyc + Convert.ToBase64String(Rc4(payload, cryptkey)).Replace("=", "");
    }

    public static string Decode(string msg, string rc4Key)
    {
        var key = Md5(rc4Key);
        var keya = Md5(key.Substring(0, 16));
        var keyb = Md5(key.Substring(16, 16));
        var keyc = msg.Substring(0, 4);
        var body = msg.Substring(4);
        body = body.PadRight(body.Length + ((4 - body.Length % 4) % 4), '=');
        var cryptkey = Encoding.UTF8.GetBytes(keya + Md5(keya + keyc));
        var result = Encoding.UTF8.GetString(Rc4(Convert.FromBase64String(body), cryptkey));
        var content = result.Substring(26);
        return result.Substring(10, 16) == Md5(content + keyb).Substring(0, 16) ? content : "";
    }

    public static string MakeSign(string data, string appKey) => Md5(data + appKey);
}