seg/trabalho4/tgs.py

from common import *
from AES import AESCipher
import socket
import os
import base64
import time

HOST = "127.0.0.1"
PORT = TGS_PORT

TGS_KEY = os.urandom(32)

def process_message(message):
    message = message.split("||")

    if message[0] == "getkey":
        print('ktgs', TGS_KEY)
        return f"{base64.b64encode(TGS_KEY)}"
    if message[0] == "request":
        """
            T_c_tgs = {ID_C + T_R + K_c_tgs}K_tgs

        M3 = [{ID_C + ID_S + T_R + N2}K_c_tgs + T_c_tgs]
        M4 = [{K_c_s + T_A + N2}K_c_tgs + T_c_s]
            T_c_s = {ID_C + T_A + K_c_s}K_s
        """
        body = message[1].split("<>")
        K_tgs = TGS_KEY

        M3 = body[0]
        M3 = M3.split("<>")
        M3_inner = M3[0]
        T_c_tgs = body[1]

        M3_AES = AESCipher(K_tgs)
        T_c_tgs = M3_AES.decrypt(T_c_tgs)
        T_c_tgs = T_c_tgs.split("<>")
        ID_C = T_c_tgs[0]
        T_R = int(T_c_tgs[1])
        K_c_tgs = eval(T_c_tgs[2])

        M3_inner_AES = AESCipher(K_c_tgs)
        M3_inner = M3_inner_AES.decrypt(M3_inner)
        M3_inner = M3_inner.split("<>")
        ID_S = M3_inner[1]
        N2 = M3_inner[3]

        # generate M4
        K_c_s = os.urandom(16)
        T_A = 600 if T_R > 600 else T_R
        T_A = int(time.time()) + T_A
        T_c_s = f"{ID_C}<>{T_A}<>{K_c_s}"

        K_s = get_ks()
        T_c_s_AES = AESCipher(K_s)
        T_c_s = T_c_s_AES.encrypt(T_c_s)

        M4_inner = f"{K_c_s}<>{T_A}<>{N2}"
        M4_inner_AES = AESCipher(K_c_tgs)
        M4_inner = M4_inner_AES.encrypt(M4_inner)

        print("Sending M4", f"[{K_c_s}<>{T_A}<>{N2}]<>[T_c_s] | T_c_s = [{ID_C}<>{T_A}<>K_c_s]")

        M4 = f"{M4_inner}<>{T_c_s}"
        return M4

def get_ks():
    message = f"getkey"
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.connect((HOST, SERVICE_PORT))
        s.sendall(message.encode())

        data = s.recv(4096)
        data = data.decode()
        key = eval(data)
        key = base64.b64decode(key)
        return key

def main():
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.bind((HOST, PORT))
        s.listen()
        while True:
            conn, addr = s.accept()
            with conn:
                all_data = ""
                data = conn.recv(4096)
                all_data += data.decode()

                response = process_message(all_data)

                conn.sendall(response.encode())

if __name__ == "__main__":
    main()