# Snyk Fetch the Flag CTF 2023 writeup: Honey Baked Messages

Written by:

November 30, 2023

Thanks for playing Fetch with us! Congrats to the thousands of players who joined us for Fetch the Flag CTF. If you were at Snyk’s 2023 Fetch the Flag and are looking for the answer to the Honey Baked Messages challenge, you’ve come to the right place. Let’s walk through the solution together!

This challenge focuses on the idea of Hamming codes. Hamming codes are a type of error-correcting codes. This challenge uses the (7, 4) version of Hamming codes.

The challenge consists of these parts:

1. Understand that this is Hamming coding.

2. Read in each line of the file.

3. Determine the needed H matrix for the problem.

4. Error correct the entire file and get the flag.

Here is the `solve.py` solution script:

``````import numpy as np

H = np.array(
[
[1, 1, 1, 0, 1, 0, 0],
[0, 1, 1, 1, 0, 1, 0],
[1, 1, 0, 1, 0, 0, 1]
]
)
errors = {
"000":None,
"001": 6,
"010": 5,
"011": 3,
"100": 4,
"101": 0,
"110": 2,
"111": 1
}

def np2usable(nparr):
return np.array2string(nparr).replace(" ", "" ).replace("[", "").replace(']', "")

def fixErrs(hamming):
error = (np.matmul(H, hamming)%2)
err_idx = errors[np2usable(error)]
if err_idx != None:
# print(err_idx)
hamming[err_idx] +=1
hamming[err_idx] %= 2

return hamming[:4]

data = []
code = np.fromstring(" ".join(line.strip("\n")), dtype = int, sep=" ")
data.append(np2usable(fixErrs(code)))
split_chars = (list(zip(*(iter(data),) * 2)))

[print(chr(int(j+k, 2)), end="") for j,k in split_chars ]``````

## Thanks for making Fetch happen!

A huge thank you to all the teams in Fetch the Flag 2023! It was great seeing all of you there and you can always find me on YouTube.

Here are the writeups for the other 2023 challenges. Dig in!

Posted in:Ctf

Snyk is a developer security platform. Integrating directly into development tools, workflows, and automation pipelines, Snyk makes it easy for teams to find, prioritize, and fix security vulnerabilities in code, dependencies, containers, and infrastructure as code. Supported by industry-leading application and security intelligence, Snyk puts security expertise in any developer’s toolkit.