606 lines
23 KiB
Python
606 lines
23 KiB
Python
# Copyright 2018 Nordic Semiconductor ASA
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# Copyright 2017-2020 Linaro Limited
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# Copyright 2019-2021 Arm Limited
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#
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# SPDX-License-Identifier: Apache-2.0
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""
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Image signing and management.
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"""
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from . import version as versmod
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from .boot_record import create_sw_component_data
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import click
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from enum import Enum
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from intelhex import IntelHex
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import hashlib
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import struct
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import os.path
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from .keys import rsa, ecdsa, x25519
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from cryptography.hazmat.primitives.asymmetric import ec, padding
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from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey
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from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
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from cryptography.hazmat.primitives.kdf.hkdf import HKDF
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from cryptography.hazmat.primitives.serialization import Encoding, PublicFormat
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from cryptography.hazmat.backends import default_backend
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from cryptography.hazmat.primitives import hashes, hmac
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from cryptography.exceptions import InvalidSignature
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IMAGE_MAGIC = 0x96f3b83d
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IMAGE_HEADER_SIZE = 32
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BIN_EXT = "bin"
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INTEL_HEX_EXT = "hex"
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DEFAULT_MAX_SECTORS = 128
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MAX_ALIGN = 8
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DEP_IMAGES_KEY = "images"
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DEP_VERSIONS_KEY = "versions"
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MAX_SW_TYPE_LENGTH = 12 # Bytes
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# Image header flags.
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IMAGE_F = {
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'PIC': 0x0000001,
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'ENCRYPTED_AES128': 0x0000004,
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'ENCRYPTED_AES256': 0x0000008,
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'NON_BOOTABLE': 0x0000010,
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'RAM_LOAD': 0x0000020,
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'ROM_FIXED': 0x0000100,
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}
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TLV_VALUES = {
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'KEYHASH': 0x01,
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'PUBKEY': 0x02,
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'SHA256': 0x10,
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'RSA2048': 0x20,
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'ECDSA224': 0x21,
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'ECDSA256': 0x22,
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'RSA3072': 0x23,
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'ED25519': 0x24,
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'ENCRSA2048': 0x30,
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'ENCKW': 0x31,
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'ENCEC256': 0x32,
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'ENCX25519': 0x33,
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'DEPENDENCY': 0x40,
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'SEC_CNT': 0x50,
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'BOOT_RECORD': 0x60,
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}
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TLV_SIZE = 4
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TLV_INFO_SIZE = 4
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TLV_INFO_MAGIC = 0x6907
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TLV_PROT_INFO_MAGIC = 0x6908
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boot_magic = bytes([
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0x77, 0xc2, 0x95, 0xf3,
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0x60, 0xd2, 0xef, 0x7f,
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0x35, 0x52, 0x50, 0x0f,
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0x2c, 0xb6, 0x79, 0x80, ])
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STRUCT_ENDIAN_DICT = {
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'little': '<',
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'big': '>'
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}
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VerifyResult = Enum('VerifyResult',
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"""
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OK INVALID_MAGIC INVALID_TLV_INFO_MAGIC INVALID_HASH
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INVALID_SIGNATURE
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""")
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class TLV():
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def __init__(self, endian, magic=TLV_INFO_MAGIC):
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self.magic = magic
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self.buf = bytearray()
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self.endian = endian
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def __len__(self):
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return TLV_INFO_SIZE + len(self.buf)
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def add(self, kind, payload):
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"""
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Add a TLV record. Kind should be a string found in TLV_VALUES above.
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"""
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e = STRUCT_ENDIAN_DICT[self.endian]
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if isinstance(kind, int):
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buf = struct.pack(e + 'BBH', kind, 0, len(payload))
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else:
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buf = struct.pack(e + 'BBH', TLV_VALUES[kind], 0, len(payload))
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self.buf += buf
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self.buf += payload
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def get(self):
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if len(self.buf) == 0:
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return bytes()
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e = STRUCT_ENDIAN_DICT[self.endian]
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header = struct.pack(e + 'HH', self.magic, len(self))
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return header + bytes(self.buf)
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class Image():
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def __init__(self, version=None, header_size=IMAGE_HEADER_SIZE,
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pad_header=False, pad=False, confirm=False, align=1,
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slot_size=0, max_sectors=DEFAULT_MAX_SECTORS,
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overwrite_only=False, endian="little", load_addr=0,
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rom_fixed=None, erased_val=None, save_enctlv=False,
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security_counter=None):
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if load_addr and rom_fixed:
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raise click.UsageError("Can not set rom_fixed and load_addr at the same time")
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self.version = version or versmod.decode_version("0")
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self.header_size = header_size
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self.pad_header = pad_header
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self.pad = pad
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self.confirm = confirm
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self.align = align
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self.slot_size = slot_size
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self.max_sectors = max_sectors
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self.overwrite_only = overwrite_only
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self.endian = endian
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self.base_addr = None
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self.load_addr = 0 if load_addr is None else load_addr
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self.rom_fixed = rom_fixed
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self.erased_val = 0xff if erased_val is None else int(erased_val, 0)
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self.payload = []
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self.enckey = None
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self.save_enctlv = save_enctlv
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self.enctlv_len = 0
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if security_counter == 'auto':
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# Security counter has not been explicitly provided,
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# generate it from the version number
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self.security_counter = ((self.version.major << 24)
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+ (self.version.minor << 16)
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+ self.version.revision)
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else:
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self.security_counter = security_counter
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def __repr__(self):
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return "<Image version={}, header_size={}, security_counter={}, \
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base_addr={}, load_addr={}, align={}, slot_size={}, \
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max_sectors={}, overwrite_only={}, endian={} format={}, \
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payloadlen=0x{:x}>".format(
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self.version,
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self.header_size,
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self.security_counter,
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self.base_addr if self.base_addr is not None else "N/A",
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self.load_addr,
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self.align,
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self.slot_size,
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self.max_sectors,
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self.overwrite_only,
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self.endian,
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self.__class__.__name__,
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len(self.payload))
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def load(self, path):
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"""Load an image from a given file"""
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ext = os.path.splitext(path)[1][1:].lower()
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try:
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if ext == INTEL_HEX_EXT:
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ih = IntelHex(path)
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self.payload = ih.tobinarray()
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self.base_addr = ih.minaddr()
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else:
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with open(path, 'rb') as f:
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self.payload = f.read()
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except FileNotFoundError:
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raise click.UsageError("Input file not found")
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# Add the image header if needed.
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if self.pad_header and self.header_size > 0:
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if self.base_addr:
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# Adjust base_addr for new header
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self.base_addr -= self.header_size
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self.payload = bytes([self.erased_val] * self.header_size) + \
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self.payload
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self.check_header()
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def save(self, path, hex_addr=None):
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"""Save an image from a given file"""
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ext = os.path.splitext(path)[1][1:].lower()
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if ext == INTEL_HEX_EXT:
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# input was in binary format, but HEX needs to know the base addr
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if self.base_addr is None and hex_addr is None:
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raise click.UsageError("No address exists in input file "
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"neither was it provided by user")
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h = IntelHex()
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if hex_addr is not None:
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self.base_addr = hex_addr
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h.frombytes(bytes=self.payload, offset=self.base_addr)
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if self.pad:
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trailer_size = self._trailer_size(self.align, self.max_sectors,
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self.overwrite_only,
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self.enckey,
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self.save_enctlv,
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self.enctlv_len)
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trailer_addr = (self.base_addr + self.slot_size) - trailer_size
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padding = bytearray([self.erased_val] *
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(trailer_size - len(boot_magic)))
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if self.confirm and not self.overwrite_only:
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padding[-MAX_ALIGN] = 0x01 # image_ok = 0x01
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padding += boot_magic
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h.puts(trailer_addr, bytes(padding))
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h.tofile(path, 'hex')
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else:
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if self.pad:
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self.pad_to(self.slot_size)
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with open(path, 'wb') as f:
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f.write(self.payload)
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def check_header(self):
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if self.header_size > 0 and not self.pad_header:
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if any(v != 0 for v in self.payload[0:self.header_size]):
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raise click.UsageError("Header padding was not requested and "
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"image does not start with zeros")
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def check_trailer(self):
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if self.slot_size > 0:
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tsize = self._trailer_size(self.align, self.max_sectors,
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self.overwrite_only, self.enckey,
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self.save_enctlv, self.enctlv_len)
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padding = self.slot_size - (len(self.payload) + tsize)
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if padding < 0:
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msg = "Image size (0x{:x}) + trailer (0x{:x}) exceeds " \
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"requested size 0x{:x}".format(
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len(self.payload), tsize, self.slot_size)
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raise click.UsageError(msg)
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def ecies_hkdf(self, enckey, plainkey):
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if isinstance(enckey, ecdsa.ECDSA256P1Public):
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newpk = ec.generate_private_key(ec.SECP256R1(), default_backend())
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shared = newpk.exchange(ec.ECDH(), enckey._get_public())
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else:
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newpk = X25519PrivateKey.generate()
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shared = newpk.exchange(enckey._get_public())
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derived_key = HKDF(
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algorithm=hashes.SHA256(), length=48, salt=None,
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info=b'MCUBoot_ECIES_v1', backend=default_backend()).derive(shared)
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encryptor = Cipher(algorithms.AES(derived_key[:16]),
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modes.CTR(bytes([0] * 16)),
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backend=default_backend()).encryptor()
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cipherkey = encryptor.update(plainkey) + encryptor.finalize()
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mac = hmac.HMAC(derived_key[16:], hashes.SHA256(),
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backend=default_backend())
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mac.update(cipherkey)
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ciphermac = mac.finalize()
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if isinstance(enckey, ecdsa.ECDSA256P1Public):
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pubk = newpk.public_key().public_bytes(
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encoding=Encoding.X962,
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format=PublicFormat.UncompressedPoint)
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else:
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pubk = newpk.public_key().public_bytes(
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encoding=Encoding.Raw,
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format=PublicFormat.Raw)
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return cipherkey, ciphermac, pubk
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def create(self, key, public_key_format, enckey, dependencies=None,
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sw_type=None, custom_tlvs=None, encrypt_keylen=128):
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self.enckey = enckey
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# Calculate the hash of the public key
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if key is not None:
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pub = key.get_public_bytes()
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sha = hashlib.sha256()
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sha.update(pub)
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pubbytes = sha.digest()
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else:
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pubbytes = bytes(hashlib.sha256().digest_size)
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protected_tlv_size = 0
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if self.security_counter is not None:
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# Size of the security counter TLV: header ('HH') + payload ('I')
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# = 4 + 4 = 8 Bytes
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protected_tlv_size += TLV_SIZE + 4
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if sw_type is not None:
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if len(sw_type) > MAX_SW_TYPE_LENGTH:
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msg = "'{}' is too long ({} characters) for sw_type. Its " \
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"maximum allowed length is 12 characters.".format(
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sw_type, len(sw_type))
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raise click.UsageError(msg)
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image_version = (str(self.version.major) + '.'
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+ str(self.version.minor) + '.'
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+ str(self.version.revision))
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# The image hash is computed over the image header, the image
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# itself and the protected TLV area. However, the boot record TLV
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# (which is part of the protected area) should contain this hash
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# before it is even calculated. For this reason the script fills
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# this field with zeros and the bootloader will insert the right
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# value later.
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digest = bytes(hashlib.sha256().digest_size)
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# Create CBOR encoded boot record
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boot_record = create_sw_component_data(sw_type, image_version,
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"SHA256", digest,
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pubbytes)
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protected_tlv_size += TLV_SIZE + len(boot_record)
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if dependencies is not None:
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# Size of a Dependency TLV = Header ('HH') + Payload('IBBHI')
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# = 4 + 12 = 16 Bytes
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dependencies_num = len(dependencies[DEP_IMAGES_KEY])
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protected_tlv_size += (dependencies_num * 16)
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if custom_tlvs is not None:
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for value in custom_tlvs.values():
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protected_tlv_size += TLV_SIZE + len(value)
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if protected_tlv_size != 0:
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# Add the size of the TLV info header
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protected_tlv_size += TLV_INFO_SIZE
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# At this point the image is already on the payload
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#
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# This adds the padding if image is not aligned to the 16 Bytes
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# in encrypted mode
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if self.enckey is not None:
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pad_len = len(self.payload) % 16
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if pad_len > 0:
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pad = bytes(16 - pad_len)
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if isinstance(self.payload, bytes):
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self.payload += pad
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else:
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self.payload.extend(pad)
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# This adds the header to the payload as well
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if encrypt_keylen == 256:
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self.add_header(enckey, protected_tlv_size, 256)
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else:
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self.add_header(enckey, protected_tlv_size)
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prot_tlv = TLV(self.endian, TLV_PROT_INFO_MAGIC)
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# Protected TLVs must be added first, because they are also included
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# in the hash calculation
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protected_tlv_off = None
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if protected_tlv_size != 0:
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e = STRUCT_ENDIAN_DICT[self.endian]
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if self.security_counter is not None:
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payload = struct.pack(e + 'I', self.security_counter)
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prot_tlv.add('SEC_CNT', payload)
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if sw_type is not None:
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prot_tlv.add('BOOT_RECORD', boot_record)
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if dependencies is not None:
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for i in range(dependencies_num):
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payload = struct.pack(
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e + 'B3x'+'BBHI',
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int(dependencies[DEP_IMAGES_KEY][i]),
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dependencies[DEP_VERSIONS_KEY][i].major,
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dependencies[DEP_VERSIONS_KEY][i].minor,
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dependencies[DEP_VERSIONS_KEY][i].revision,
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dependencies[DEP_VERSIONS_KEY][i].build
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)
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prot_tlv.add('DEPENDENCY', payload)
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if custom_tlvs is not None:
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for tag, value in custom_tlvs.items():
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prot_tlv.add(tag, value)
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protected_tlv_off = len(self.payload)
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self.payload += prot_tlv.get()
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tlv = TLV(self.endian)
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# Note that ecdsa wants to do the hashing itself, which means
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# we get to hash it twice.
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sha = hashlib.sha256()
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sha.update(self.payload)
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digest = sha.digest()
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tlv.add('SHA256', digest)
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if key is not None:
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if public_key_format == 'hash':
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tlv.add('KEYHASH', pubbytes)
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else:
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tlv.add('PUBKEY', pub)
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# `sign` expects the full image payload (sha256 done internally),
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# while `sign_digest` expects only the digest of the payload
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if hasattr(key, 'sign'):
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sig = key.sign(bytes(self.payload))
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else:
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sig = key.sign_digest(digest)
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tlv.add(key.sig_tlv(), sig)
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# At this point the image was hashed + signed, we can remove the
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# protected TLVs from the payload (will be re-added later)
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if protected_tlv_off is not None:
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self.payload = self.payload[:protected_tlv_off]
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if enckey is not None:
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if encrypt_keylen == 256:
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plainkey = os.urandom(32)
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else:
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plainkey = os.urandom(16)
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if isinstance(enckey, rsa.RSAPublic):
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cipherkey = enckey._get_public().encrypt(
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plainkey, padding.OAEP(
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mgf=padding.MGF1(algorithm=hashes.SHA256()),
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algorithm=hashes.SHA256(),
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label=None))
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self.enctlv_len = len(cipherkey)
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tlv.add('ENCRSA2048', cipherkey)
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elif isinstance(enckey, (ecdsa.ECDSA256P1Public,
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x25519.X25519Public)):
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cipherkey, mac, pubk = self.ecies_hkdf(enckey, plainkey)
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enctlv = pubk + mac + cipherkey
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self.enctlv_len = len(enctlv)
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if isinstance(enckey, ecdsa.ECDSA256P1Public):
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tlv.add('ENCEC256', enctlv)
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else:
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tlv.add('ENCX25519', enctlv)
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nonce = bytes([0] * 16)
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cipher = Cipher(algorithms.AES(plainkey), modes.CTR(nonce),
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backend=default_backend())
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encryptor = cipher.encryptor()
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img = bytes(self.payload[self.header_size:])
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self.payload[self.header_size:] = \
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encryptor.update(img) + encryptor.finalize()
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self.payload += prot_tlv.get()
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self.payload += tlv.get()
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self.check_trailer()
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def add_header(self, enckey, protected_tlv_size, aes_length=128):
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"""Install the image header."""
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flags = 0
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if enckey is not None:
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if aes_length == 128:
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flags |= IMAGE_F['ENCRYPTED_AES128']
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else:
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flags |= IMAGE_F['ENCRYPTED_AES256']
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if self.load_addr != 0:
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# Indicates that this image should be loaded into RAM
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|
# instead of run directly from flash.
|
|
flags |= IMAGE_F['RAM_LOAD']
|
|
if self.rom_fixed:
|
|
flags |= IMAGE_F['ROM_FIXED']
|
|
|
|
e = STRUCT_ENDIAN_DICT[self.endian]
|
|
fmt = (e +
|
|
# type ImageHdr struct {
|
|
'I' + # Magic uint32
|
|
'I' + # LoadAddr uint32
|
|
'H' + # HdrSz uint16
|
|
'H' + # PTLVSz uint16
|
|
'I' + # ImgSz uint32
|
|
'I' + # Flags uint32
|
|
'BBHI' + # Vers ImageVersion
|
|
'I' # Pad1 uint32
|
|
) # }
|
|
assert struct.calcsize(fmt) == IMAGE_HEADER_SIZE
|
|
header = struct.pack(fmt,
|
|
IMAGE_MAGIC,
|
|
self.rom_fixed or self.load_addr,
|
|
self.header_size,
|
|
protected_tlv_size, # TLV Info header + Protected TLVs
|
|
len(self.payload) - self.header_size, # ImageSz
|
|
flags,
|
|
self.version.major,
|
|
self.version.minor or 0,
|
|
self.version.revision or 0,
|
|
self.version.build or 0,
|
|
0) # Pad1
|
|
self.payload = bytearray(self.payload)
|
|
self.payload[:len(header)] = header
|
|
|
|
def _trailer_size(self, write_size, max_sectors, overwrite_only, enckey,
|
|
save_enctlv, enctlv_len):
|
|
# NOTE: should already be checked by the argument parser
|
|
magic_size = 16
|
|
if overwrite_only:
|
|
return MAX_ALIGN * 2 + magic_size
|
|
else:
|
|
if write_size not in set([1, 2, 4, 8]):
|
|
raise click.BadParameter("Invalid alignment: {}".format(
|
|
write_size))
|
|
m = DEFAULT_MAX_SECTORS if max_sectors is None else max_sectors
|
|
trailer = m * 3 * write_size # status area
|
|
if enckey is not None:
|
|
if save_enctlv:
|
|
# TLV saved by the bootloader is aligned
|
|
keylen = (int((enctlv_len - 1) / MAX_ALIGN) + 1) * MAX_ALIGN
|
|
else:
|
|
keylen = 16
|
|
trailer += keylen * 2 # encryption keys
|
|
trailer += MAX_ALIGN * 4 # image_ok/copy_done/swap_info/swap_size
|
|
trailer += magic_size
|
|
return trailer
|
|
|
|
def pad_to(self, size):
|
|
"""Pad the image to the given size, with the given flash alignment."""
|
|
tsize = self._trailer_size(self.align, self.max_sectors,
|
|
self.overwrite_only, self.enckey,
|
|
self.save_enctlv, self.enctlv_len)
|
|
padding = size - (len(self.payload) + tsize)
|
|
pbytes = bytearray([self.erased_val] * padding)
|
|
pbytes += bytearray([self.erased_val] * (tsize - len(boot_magic)))
|
|
if self.confirm and not self.overwrite_only:
|
|
pbytes[-MAX_ALIGN] = 0x01 # image_ok = 0x01
|
|
pbytes += boot_magic
|
|
self.payload += pbytes
|
|
|
|
@staticmethod
|
|
def verify(imgfile, key):
|
|
with open(imgfile, "rb") as f:
|
|
b = f.read()
|
|
|
|
magic, _, header_size, _, img_size = struct.unpack('IIHHI', b[:16])
|
|
version = struct.unpack('BBHI', b[20:28])
|
|
|
|
if magic != IMAGE_MAGIC:
|
|
return VerifyResult.INVALID_MAGIC, None, None
|
|
|
|
tlv_off = header_size + img_size
|
|
tlv_info = b[tlv_off:tlv_off+TLV_INFO_SIZE]
|
|
magic, tlv_tot = struct.unpack('HH', tlv_info)
|
|
if magic == TLV_PROT_INFO_MAGIC:
|
|
tlv_off += tlv_tot
|
|
tlv_info = b[tlv_off:tlv_off+TLV_INFO_SIZE]
|
|
magic, tlv_tot = struct.unpack('HH', tlv_info)
|
|
|
|
if magic != TLV_INFO_MAGIC:
|
|
return VerifyResult.INVALID_TLV_INFO_MAGIC, None, None
|
|
|
|
sha = hashlib.sha256()
|
|
prot_tlv_size = tlv_off
|
|
sha.update(b[:prot_tlv_size])
|
|
digest = sha.digest()
|
|
|
|
tlv_end = tlv_off + tlv_tot
|
|
tlv_off += TLV_INFO_SIZE # skip tlv info
|
|
while tlv_off < tlv_end:
|
|
tlv = b[tlv_off:tlv_off+TLV_SIZE]
|
|
tlv_type, _, tlv_len = struct.unpack('BBH', tlv)
|
|
if tlv_type == TLV_VALUES["SHA256"]:
|
|
off = tlv_off + TLV_SIZE
|
|
if digest == b[off:off+tlv_len]:
|
|
if key is None:
|
|
return VerifyResult.OK, version, digest
|
|
else:
|
|
return VerifyResult.INVALID_HASH, None, None
|
|
elif key is not None and tlv_type == TLV_VALUES[key.sig_tlv()]:
|
|
off = tlv_off + TLV_SIZE
|
|
tlv_sig = b[off:off+tlv_len]
|
|
payload = b[:prot_tlv_size]
|
|
try:
|
|
if hasattr(key, 'verify'):
|
|
key.verify(tlv_sig, payload)
|
|
else:
|
|
key.verify_digest(tlv_sig, digest)
|
|
return VerifyResult.OK, version, digest
|
|
except InvalidSignature:
|
|
# continue to next TLV
|
|
pass
|
|
tlv_off += TLV_SIZE + tlv_len
|
|
return VerifyResult.INVALID_SIGNATURE, None, None
|