uFNuWJq3

1using System;
2using System.Collections.Generic;
3using System.Linq;
4using System.Text;
5using System.Threading.Tasks;
6using System.Net;
7using System.Net.Sockets;
8using System.Numerics;
9
10namespace WireSharkLesson
11{
12    public struct Datas
13    {
14        public BigInteger p;
15        public BigInteger g;
16        public BigInteger message;
17    }
18    class Program
19    {
20        static void Main(string[] args)
21        {
22            Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
23            IPEndPoint ep = new IPEndPoint(IPAddress.Any, 5555);
24            socket.Bind(ep);
25
26            Dictionary<IPEndPoint, BigInteger> clients = new Dictionary<IPEndPoint, BigInteger>();
27            Random r = new Random();
28
29            //read p, read g, read alice message SHORT PREFIX
30            while (true)
31            {
32                byte[] buffer = new byte[1024];
33                EndPoint clientEP = new IPEndPoint(IPAddress.Any, 2000);
34                int dataReceived = socket.ReceiveFrom(buffer, ref clientEP);
35
36                if (dataReceived < 0) continue;
37                if (!clients.ContainsKey((IPEndPoint)clientEP))
38                {
39
40                    Datas d = new Datas();
41
42                    short pLength = BitConverter.ToInt16(buffer, 0);
43                    byte[] p = new byte[pLength];
44                    Buffer.BlockCopy(buffer, 2, p, 0, pLength);
45                    d.p = new BigInteger(p);
46
47                    d.g = buffer[2 + pLength];
48
49                    short messageLength = BitConverter.ToInt16(buffer, 3 + pLength);
50                    byte[] message = new byte[messageLength];
51                    Buffer.BlockCopy(buffer, 5 + pLength, message, 0, messageLength);
52                    d.message = new BigInteger(message);
53
54                    int myRandom = r.Next();        //bob secret number
55
56                    BigInteger secretKey = BigInteger.ModPow(d.message, myRandom, d.p);
57                    clients.Add((IPEndPoint)clientEP, secretKey);
58
59                    BigInteger myMessage = (BigInteger.ModPow(d.g, myRandom, d.p));
60
61                    List<byte> toSend = new List<byte>();
62
63                    toSend.AddRange(BitConverter.GetBytes((short)myMessage.ToByteArray().Length));
64                    toSend.AddRange(myMessage.ToByteArray());
65
66                    socket.SendTo(toSend.ToArray(), clientEP);
67                    Console.WriteLine("data received "+ myMessage);
68                }
69                else
70                {
71                    List<byte> decriptedData = new List<byte>();
72                    byte[] clientKey = clients[(IPEndPoint)clientEP].ToByteArray();
73                    for (int i = 0; i < dataReceived; i++)
74                    {
75                        decriptedData.Add(buffer[i] ^= clientKey[i]);
76                    }
77
78                    string text = Encoding.ASCII.GetString(decriptedData.ToArray());
79                    Console.WriteLine(text);
80                }
81            }
82
83
84        }
85    }
86}