lost_list.py

import binascii
import socket
import sys

HOST = 'challs.xmas.htsp.ro'
PORT = 1002

# Come up with a way to encode a word into a number, and binary search.
alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

log = open("net.log", "wb")

def send(s, data):
    if isinstance(data, str):
        data = bytearray(data, 'ascii')
    #print(f"Sending {len(data)} bytes: {data}")
    s.sendall(data)
    log.write(data)
    s.sendall(b'\n')
    log.write(b'\n')
    log.flush()

def recv_until(s, q):
    buf = b""
    while not buf.endswith(q):
        data = s.recv(1)
        buf += data
        log.write(data)
        log.flush()

    #print(f"Received: {q}")
    return buf.decode("utf-8")

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))


raw_cmd = "53616e74612773313333374956343230ab0c288b0ae26eaf8adbcf00bddf35fa"
cmd = binascii.unhexlify(raw_cmd)
iv = cmd[:16]
c = cmd[16:]


def xor(b1, b2):
    return bytes(a ^ b for a, b in zip(b1, b2))


def prompt():
    sys.stdout.write(recv_until(s, b"~$ "))


def run(c):
    hexcmd = binascii.hexlify(c)
    send(s, hexcmd)


def pad(bs, l):
    if len(bs) > l:
        raise Exception("Command too long")
    # Pad
    if len(bs) < l:
        diff = l - len(bs)
        bs = bs + bytes([diff] * diff)

    return bs


def build_cmd(bs):
    plain = pad(b"ls", 16)
    c2 = xor(plain, iv)
    bs = pad(bs, 16)
    new_iv = xor(c2, bs)
    return new_iv + c


prompt()
while True:
    text = input()
    ls = build_cmd(bytearray(text, "ascii"))
    run(ls)
    prompt()