> For the complete documentation index, see [llms.txt](https://ctf.zeyu2001.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ctf.zeyu2001.com/2021/umdctf-2021/bomb-2-mix-up.md).

# Bomb 2 - Mix Up

Source code:

```python
import string
import random
import socket
import threading
from _thread import *
import time

FLAG = "REDACTED"
code = "REDACTED"
HOST = '0.0.0.0'  # Standard loopback interface address (localhost)
PORT = 12347        # Port to listen on (non-privileged ports are > 1023)

def threading(conn):
    conn.sendall(initial.encode())
    data = conn.recv(1024).decode()

    if data == "\n":
        values = give_values()
        print(values)
        print(('\n'.join(values)).encode())
        conn.sendall(('\n'.join(values)+'\n\nCode: ').encode())
        start_timer = time.perf_counter()
    else:
        conn.close()

    data = conn.recv(1024).decode().split('\n')[0]
    print(f'{data}\n{code}')
    end_timer = time.perf_counter()

    print("Start: {}\nFinish: {}\nExcecution Time: {}".format(start_timer, end_timer, int(end_timer - start_timer)))

    if data and data in code:
        if int(end_timer - start_timer) <= 5:
            conn.sendall("\nCongrats! You've successfully defused the bomb! Phew... Here is a flag for our appreciation:\n{}".format(FLAG).encode())
        else:
            conn.sendall("That took more than 5 seconds :(".encode())
    else:
        conn.sendall("That was wrong :(".encode())
    print('closing connection to', addr)
    conn.close()

def print_mode(mstring):
    print(max(set(mstring), key=mstring.count))

def generate_string():
    possible = string.ascii_lowercase + string.ascii_lowercase + string.digits + '_-{}'
    return [random.choice(possible) for i in range(1000)]

def give_values():
    total = []
    for i in range(len(code)):
        test = generate_string()
        c = code[i]
        for i in range(100):
            num = random.randint(0,999)
            test[num] = c
        total.append(''.join(test))
    return total

initial = "Hurry someone lost the code that stops the bomb! Find and decode it. Time is running out...\n\nPress Enter to begin"

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.bind((HOST, PORT))
    s.listen()
    while True:
        conn, addr = s.accept()
        print("\n")
        start_new_thread(threading, (conn, ))
    s.close()
```

Analysing the `give_values()` function, we can see that every line of data generated corresponds to one character in the `code`, and that this character will appear very frequently (\~100 times) in that line of data. The key is therefore to maintain a frequency dictionary and extract the most frequent character for each line.

```python
from pwn import *

conn = remote('chals3.umdctf.io', 6000)

conn.recv()
conn.send('\n')
data = conn.recvuntil('Code').decode()

lines = data.split('\n')[:-1]

chars = []

for line in lines:

    if line and 'Code' not in line:

        freq_dict = {}
        for char in line:
            if char in freq_dict:
                freq_dict[char] += 1
            else:
                freq_dict[char] = 0

        freq_dict = {k: v for k, v in sorted(freq_dict.items(), key=lambda item: -item[1])}
        most_freq = list(freq_dict.keys())[0]

        chars.append(most_freq)

print(''.join(chars))
conn.send(''.join(chars))
conn.recv()
print(conn.recv())
```

![](/files/-MYcEYUWcV_H4xz6r6ax)


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://ctf.zeyu2001.com/2021/umdctf-2021/bomb-2-mix-up.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.