# krack_sim.py - Simulates reinstallation of an already-used PTK
import hashlib, os

class AccessPoint:
    def __init__(self):
        self.anonce = os.urandom(32)
        self.ptk = None

    def send_msg3(self, snonce):
        # Normally would install PTK, but here we resend msg3 to trigger reinstall
        self.ptk = hashlib.sha256(b"PMK" + self.anonce + snonce).digest()
        print("Installed PTK")
        return self.ptk

class Client:
    def __init__(self):
        self.snonce = os.urandom(32)
        self.ptk = None

    def receive_msg3(self, ap):
        self.ptk = ap.send_msg3(self.snonce)
        # Vulnerability: if AP resends msg3, nonce reuse may reset counters
        print("Client installed PTK")

ap = AccessPoint()
client = Client()
client.receive_msg3(ap)   # first install
client.receive_msg3(ap)   # reinstallation! Nonce reused, replay possible

python krack_sim.py