Roman Okhrimenko | 977b375 | 2022-03-31 14:40:48 +0300 | [diff] [blame] | 1 | """ |
| 2 | Copyright (c) 2021 Cypress Semiconductor Corporation |
| 3 | |
| 4 | Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | you may not use this file except in compliance with the License. |
| 6 | You may obtain a copy of the License at |
| 7 | |
| 8 | http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | |
| 10 | Unless required by applicable law or agreed to in writing, software |
| 11 | distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | See the License for the specific language governing permissions and |
| 14 | limitations under the License. |
| 15 | """ |
| 16 | import os |
| 17 | import struct |
| 18 | from cryptography.hazmat.primitives.ciphers import ( |
| 19 | Cipher, algorithms, modes |
| 20 | ) |
| 21 | |
| 22 | NONCE_SIZE = 12 |
| 23 | |
| 24 | class EncryptorMXS40Sv2: |
| 25 | def __init__(self, key, nonce, initial_counter=0): |
| 26 | # with open(key_path, 'rb') as f: |
| 27 | # self.key = f.read() |
| 28 | self.key = key |
| 29 | self.nonce = nonce |
| 30 | self.counter = 0 |
| 31 | self.initial_counter = initial_counter |
| 32 | cipher = Cipher(algorithms.AES(key), modes.ECB()) |
| 33 | self.encryptor = cipher.encryptor() |
| 34 | |
| 35 | def _load(self, image_path): |
| 36 | with open(image_path, 'rb') as f: |
| 37 | image = f.read() |
| 38 | return image |
| 39 | |
| 40 | def _save(self, data, output_path): |
| 41 | with open(output_path, 'wb') as f: |
| 42 | f.write(data) |
| 43 | |
| 44 | def update(self, data): |
| 45 | """ |
| 46 | Encrypts a byte array using a customized AES-CTR mode |
| 47 | where a counter is incremented by 16 per block. |
| 48 | A nonce format is (128 bit): |
| 49 | bits 0...31 - counter + initial values |
| 50 | bits 32...127 - random nonce |
| 51 | """ |
| 52 | chunk_size = 16 |
| 53 | counter = self.counter |
| 54 | ciphertext = bytes() |
| 55 | for i in range(0, len(image), chunk_size): |
| 56 | indata = struct.pack('<I', initial_counter + counter) + nonce |
| 57 | counter += chunk_size |
| 58 | cipher_block = self.encryptor.update(indata) |
| 59 | chunk = image[i:i + chunk_size] |
| 60 | ciphertext += bytes(a ^ b for a, b in zip(chunk, cipher_block)) |
| 61 | self.counter = counter |
| 62 | return ciphertext |
| 63 | |
| 64 | def encrypt(self, image, initial_counter=0): |
| 65 | """ |
| 66 | Encrypts a byte array using a customized AES-CTR mode |
| 67 | where a counter is incremented by 16 per block. |
| 68 | A nonce format is (128 bit): |
| 69 | bits 0...31 - counter + initial values |
| 70 | bits 32...127 - random nonce |
| 71 | """ |
| 72 | chunk_size = 16 |
| 73 | counter = 0 |
| 74 | # self.initial_counter = initial_counter |
| 75 | # counter = 0 if initial_counter is None else int(initial_counter, 0) |
| 76 | # counter = initial_counter |
| 77 | ciphertext = bytes() |
| 78 | for i in range(0, len(image), chunk_size): |
| 79 | indata = struct.pack('<I', initial_counter + counter) + self.nonce[:12] |
| 80 | counter += chunk_size |
| 81 | cipher_block = self.encryptor.update(indata) |
| 82 | chunk = image[i:i + chunk_size] |
| 83 | ciphertext += bytes(a ^ b for a, b in zip(chunk, cipher_block)) |
| 84 | self.encryptor.finalize() |
| 85 | # return ciphertext, nonce |
| 86 | return ciphertext |
| 87 | |
| 88 | def encrypt_image(self, input_path, initial_counter=None, output_path=None, nonce_path=None): |
| 89 | """ |
| 90 | Encrypts an image each time using new random nonce. |
| 91 | Saves the nonce and the encrypted image to specified locations. |
| 92 | If the output locations are not given the output files are saved |
| 93 | in the same location as the input image with predefined names. |
| 94 | """ |
| 95 | image = self._load(input_path) |
| 96 | |
| 97 | nonce = os.urandom(NONCE_SIZE) |
| 98 | init = 0 if initial_counter is None else int(initial_counter, 0) |
| 99 | ciphertext, nonce = self._encrypt(image, nonce, init) |
| 100 | |
| 101 | if output_path is None: |
| 102 | output_path = '{0}_{2}{1}'.format(*os.path.splitext(input_path) + ('encrypted',)) |
| 103 | |
| 104 | if nonce_path is None: |
| 105 | nonce_path = '{0}_{2}{1}'.format(*os.path.splitext(input_path) + ('nonce',)) |
| 106 | |
| 107 | self._save(ciphertext, output_path) |
| 108 | self._save(nonce, nonce_path) |
| 109 | |
| 110 | return output_path, nonce_path |