picoCTF Solutions
picoCTF 2026General SkillsMedium

bytemancy 1

Published: March 20, 2026

Description

Can you conjure the right bytes? Download `app.py` and recover the exact input the server expects.

Setup

Download app.py

Download and read app.py to understand what byte sequence the server expects.

Launch the challenge instance and connect via netcat.

cat app.py

Solution

  1. Step 1Read the source code
    Download app.py. It asks for ASCII DECIMAL 101, 1751 times, side-by-side, no space. ASCII 101 = 'e'. The server checks your input equals 'e' * 1751.
    cat app.py
  2. Step 2Send the payload
    Generate and send a string of 1751 'e' characters. Python makes this trivial.
    python3 -c "print('e' * 1751)" | nc <HOST> <PORT_FROM_INSTANCE>
    python3 -c "import socket; s=socket.create_connection(('<HOST>', <PORT_FROM_INSTANCE>)); s.recv(512); s.sendall(b'e'*1751 + b'\n'); print(s.recv(512).decode())"

Flag

picoCTF{byt3m4ncy_1_...}

app.py asks for ASCII decimal 101 × 1751, no spaces. Send the string 'e' repeated 1751 times.