TRAFFIC LIGHTS

Walkthrough

Challenge

The player receives traffic.txt, containing a long sequence of colored traffic-light emojis.

Solution

The signals encode binary data:

• 🔴 is 0;
• 🟢 is 1;
• 🟡 separates bytes.

For example, the first group is:

🔴 🟢 🔴 🟢 🔴 🔴 🟢 🟢 🟡

That becomes 01010011, which is decimal 83 and ASCII S. Decode every group in order to recover the flag.

python3 solver.py

Output:

Securinets{r3d_gr33n_l1ghts_sp3ll_th3_l34k}

Run python3 make.py whenever the flag changes.

Reference solver

The reference solver supplied with the writeup:

#!/usr/bin/env python3

colors = {"🔴": "0", "🟢": "1"}
groups = open("traffic.txt", encoding="utf-8").read().split("🟡")
flag = bytes(
    int("".join(colors[color] for color in group.split()), 2)
    for group in groups if group.strip()
)
print(flag.decode())

Flag

Securinets{r3d_gr33n_l1ghts_sp3ll_th3_l34k}