wave - Codegate 2024 Finals

https://github.com/N0fix/rustbinsign でシンボル情報を復元できる

データにノイズが加えられているが、FFTでピークを探すと元のデータを復元できる

code:python

import numpy as np

import matplotlib.pyplot as plt

import scipy

import string

from math import sin, cos, pi

from binascii import unhexlify

from struct import unpack

import scipy.signal

def solve(y):

f_s = 400

t_fin = 1

dt = 1/f_s

N = int(f_s * t_fin)

t = np.arange(0.0, t_fin, dt)

yf = scipy.fft.fft(y)

freq = scipy.fft.fftfreq(N, d=dt)

threshold = 0.05

peaks_index, properties = scipy.signal.find_peaks(np.abs(yf), height=threshold)

max_height = 0

max_idx = 0

for i in range(len(properties'peak_heights')):

if properties'peak_heights'i > max_height:

max_height = properties'peak_heights'i

max_idx = i

return chr(peaks_indexmax_idx)

values_list = []

with open('flag.txt.encode', 'r') as f:

for line in f.readlines():

values = []

for i in range(0, len(line)-1, 16):

values.append(unpack('>d', unhexlify(linei:i+16))0)

values_list.append(np.asarray(values))

print(''.join([solve(values_listi) for i in range(len(values_list))]))