def recover_message_from_image(input_image, num_lsb):
"""Returns the message from the steganographed image"""
start = time()
if isinstance(input_image, Image.Image):
steg_image = input_image
else:
steg_image = Image.open(input_image)
color_data = [v for t in steg_image.getdata() for v in t]
file_size_tag_size = bytes_in_max_file_size(steg_image, num_lsb)
tag_bit_height = roundup(8 * file_size_tag_size / num_lsb)
bytes_to_recover = int.from_bytes(
lsb_deinterleave_list(color_data[:tag_bit_height],
8 * file_size_tag_size, num_lsb),
byteorder=sys.byteorder,
)
log.debug(f"Files read".ljust(30) + f" in {time() - start:.2f}s")
start = time()
data = lsb_deinterleave_list(color_data[tag_bit_height:],
8 * bytes_to_recover, num_lsb)
log.debug(f"{bytes_to_recover} bytes recovered".ljust(30) +
f" in {time() - start:.2f}s")
return data
def recover_message_from_image(input_image, num_lsb):
"""Returns the message from the steganographed image"""
start = time()
if isinstance(input_image, Image.Image):
steg_image = input_image
else:
steg_image = Image.open(input_image)
color_data = [v for t in steg_image.getdata() for v in t]
file_size_tag_size = bytes_in_max_file_size(steg_image, num_lsb)
tag_bit_height = roundup(8 * file_size_tag_size / num_lsb)
bytes_to_recover = int.from_bytes(
lsb_deinterleave_list(color_data[:tag_bit_height],
8 * file_size_tag_size, num_lsb),
byteorder=sys.byteorder,
)
maximum_bytes_in_image = num_lsb * len(color_data[tag_bit_height:]) // 8
if bytes_to_recover > maximum_bytes_in_image:
raise ValueError(
f"This image appears to be corrupted.\n" +
f"It claims to hold {bytes_to_recover} B, " +
f"but can only hold {maximum_bytes_in_image} B with {num_lsb} LSBs"
)
log.debug(f"Files read".ljust(30) + f" in {time() - start:.2f}s")
start = time()
data = lsb_deinterleave_list(color_data[tag_bit_height:],
8 * bytes_to_recover, num_lsb)
log.debug(f"{bytes_to_recover} bytes recovered".ljust(30) +
f" in {time() - start:.2f}s")
return data
def test_random_interleaving(self, num_trials=256, filename_length=5):
filename = "".join(
choice(string.ascii_lowercase) for _ in range(filename_length)
)
png_input_filename = filename + ".png"
payload_input_filename = filename + ".txt"
png_output_filename = filename + "_steg.png"
payload_output_filename = filename + "_recovered.txt"
np.random.seed(0)
for _ in range(num_trials):
width = np.random.randint(1, 256)
height = np.random.randint(1, 256)
num_lsb = np.random.randint(1, 9)
file_size_tag_length = roundup(
int(3 * width * height * num_lsb).bit_length() / 8
)
payload_len = (3 * width * height * num_lsb - 8 * file_size_tag_length) // 8
if payload_len < 0:
continue
self.write_random_image(png_input_filename, width=width, height=height)
self.write_random_file(payload_input_filename, num_bytes=payload_len)
try:
hide_data(
png_input_filename,
payload_input_filename,
png_output_filename,
num_lsb,
compression_level=1,
)
recover_data(png_output_filename, payload_output_filename, num_lsb)
except ValueError as e:
os.remove(png_input_filename)
os.remove(payload_input_filename)
os.remove(png_output_filename)
os.remove(payload_output_filename)
raise e
with open(payload_input_filename, "rb") as input_file, open(
payload_output_filename, "rb"
) as output_file:
input_payload_data = input_file.read()
output_payload_data = output_file.read()
os.remove(png_input_filename)
os.remove(payload_input_filename)
os.remove(png_output_filename)
os.remove(payload_output_filename)
self.assertEqual(input_payload_data, output_payload_data)
def bytes_in_max_file_size(image, num_lsb):
"""Returns the number of bits needed to store the size of the file."""
return roundup(max_bits_to_hide(image, num_lsb).bit_length() / 8)