def encrypt_png(self, in_path: PathType, out_path: PathType) -> None:
image = PngImageFile(in_path)
# convert pixels to bytes in order to encrypt them
im_bytes = bytearray(self.__get_pixels(image))
# get random IV and calculate MAC
iv = get_random_bytes(CryptoAES.block_size)
h = HMAC.new(self.__key, digestmod=SHA256)
h.update(im_bytes)
# create metadata object in order to save IV and MAC to image
metadata = PngInfo()
metadata.add_text('iv', iv.hex())
metadata.add_text('mac', h.hexdigest())
print(f'writing IV = {iv.hex()} and MAC = {h.hexdigest()} to image metadata')
# encrypt image
cipher = CryptoAES.new(self.__key, CryptoAES.MODE_ECB)
enc_data = cipher.encrypt(im_bytes)
# write image to file with metadata
image.frombytes(enc_data)
image.save(out_path, pnginfo=metadata)
def decrypt_png(self, in_path: PathType, out_path: PathType) -> None:
image = PngImageFile(in_path)
iv: Optional[str] = None
mac: Optional[str] = None
# try to get IV from metadata
try:
iv = image.text['iv']
print(f'found IV = {iv}')
except KeyError:
print('IV was not found in file')
# try to get MAC from metadata
try:
mac = image.text['mac']
print(f'found MAC = {mac}')
except KeyError:
print('MAC was not found in file')
# convert pixels to bytes in order to decrypt them
im_bytes = bytearray(self.__get_pixels(image))
# decrypt image
cipher = CryptoAES.new(self.__key, CryptoAES.MODE_ECB)
dec: bytes = cipher.decrypt(im_bytes)
# try to verify MAC
try:
self.__hmac.update(dec)
self.__hmac.verify(bytes.fromhex(mac))
print('MAC is valid')
except ValueError:
print('MAC is invalid')
# don't forget about metadata
metadata = PngInfo()
metadata.add_text('iv', iv)
metadata.add_text('mac', mac)
# save decrypted image to file
image.frombytes(dec)
image.save(out_path, pnginfo=metadata)