# Copyright 2018 Nordic Semiconductor ASA # Copyright 2017-2020 Linaro Limited # Copyright 2019-2023 Arm Limited # # SPDX-License-Identifier: Apache-2.0 # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. """ Image signing and management. """ from . import version as versmod from .boot_record import create_sw_component_data import click from enum import Enum from intelhex import IntelHex import hashlib import struct import os.path from .keys import rsa, ecdsa, x25519 from cryptography.hazmat.primitives.asymmetric import ec, padding from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes from cryptography.hazmat.primitives.kdf.hkdf import HKDF from cryptography.hazmat.primitives.serialization import Encoding, PublicFormat from cryptography.hazmat.backends import default_backend from cryptography.hazmat.primitives import hashes, hmac from cryptography.exceptions import InvalidSignature IMAGE_MAGIC = 0x96f3b83d IMAGE_HEADER_SIZE = 32 BIN_EXT = "bin" INTEL_HEX_EXT = "hex" DEFAULT_MAX_SECTORS = 128 DEFAULT_MAX_ALIGN = 8 DEP_IMAGES_KEY = "images" DEP_VERSIONS_KEY = "versions" MAX_SW_TYPE_LENGTH = 12 # Bytes # Image header flags. IMAGE_F = { 'PIC': 0x0000001, 'ENCRYPTED_AES128': 0x0000004, 'ENCRYPTED_AES256': 0x0000008, 'NON_BOOTABLE': 0x0000010, 'RAM_LOAD': 0x0000020, 'ROM_FIXED': 0x0000100, } TLV_VALUES = { 'KEYHASH': 0x01, 'PUBKEY': 0x02, 'SHA256': 0x10, 'SHA384': 0x11, 'RSA2048': 0x20, 'ECDSASIG': 0x22, 'RSA3072': 0x23, 'ED25519': 0x24, 'ENCRSA2048': 0x30, 'ENCKW': 0x31, 'ENCEC256': 0x32, 'ENCX25519': 0x33, 'DEPENDENCY': 0x40, 'SEC_CNT': 0x50, 'BOOT_RECORD': 0x60, } TLV_SIZE = 4 TLV_INFO_SIZE = 4 TLV_INFO_MAGIC = 0x6907 TLV_PROT_INFO_MAGIC = 0x6908 TLV_VENDOR_RES_MIN = 0x00a0 TLV_VENDOR_RES_MAX = 0xfffe STRUCT_ENDIAN_DICT = { 'little': '<', 'big': '>' } VerifyResult = Enum('VerifyResult', """ OK INVALID_MAGIC INVALID_TLV_INFO_MAGIC INVALID_HASH INVALID_SIGNATURE """) def align_up(num, align): assert (align & (align - 1) == 0) and align != 0 return (num + (align - 1)) & ~(align - 1) class TLV(): def __init__(self, endian, magic=TLV_INFO_MAGIC): self.magic = magic self.buf = bytearray() self.endian = endian def __len__(self): return TLV_INFO_SIZE + len(self.buf) def add(self, kind, payload): """ Add a TLV record. Kind should be a string found in TLV_VALUES above. """ e = STRUCT_ENDIAN_DICT[self.endian] if isinstance(kind, int): if not TLV_VENDOR_RES_MIN <= kind <= TLV_VENDOR_RES_MAX: msg = "Invalid custom TLV type value '0x{:04x}', allowed " \ "value should be between 0x{:04x} and 0x{:04x}".format( kind, TLV_VENDOR_RES_MIN, TLV_VENDOR_RES_MAX) raise click.UsageError(msg) buf = struct.pack(e + 'HH', kind, len(payload)) else: buf = struct.pack(e + 'BBH', TLV_VALUES[kind], 0, len(payload)) self.buf += buf self.buf += payload def get(self): if len(self.buf) == 0: return bytes() e = STRUCT_ENDIAN_DICT[self.endian] header = struct.pack(e + 'HH', self.magic, len(self)) return header + bytes(self.buf) class Image(): def __init__(self, version=None, header_size=IMAGE_HEADER_SIZE, pad_header=False, pad=False, confirm=False, align=1, slot_size=0, max_sectors=DEFAULT_MAX_SECTORS, overwrite_only=False, endian="little", load_addr=0, rom_fixed=None, erased_val=None, save_enctlv=False, security_counter=None, max_align=None): if load_addr and rom_fixed: raise click.UsageError("Can not set rom_fixed and load_addr at the same time") self.version = version or versmod.decode_version("0") self.header_size = header_size self.pad_header = pad_header self.pad = pad self.confirm = confirm self.align = align self.slot_size = slot_size self.max_sectors = max_sectors self.overwrite_only = overwrite_only self.endian = endian self.base_addr = None self.load_addr = 0 if load_addr is None else load_addr self.rom_fixed = rom_fixed self.erased_val = 0xff if erased_val is None else int(erased_val, 0) self.payload = [] self.enckey = None self.save_enctlv = save_enctlv self.enctlv_len = 0 self.max_align = max(DEFAULT_MAX_ALIGN, align) if max_align is None else int(max_align) if self.max_align == DEFAULT_MAX_ALIGN: self.boot_magic = bytes([ 0x77, 0xc2, 0x95, 0xf3, 0x60, 0xd2, 0xef, 0x7f, 0x35, 0x52, 0x50, 0x0f, 0x2c, 0xb6, 0x79, 0x80, ]) else: lsb = self.max_align & 0x00ff msb = (self.max_align & 0xff00) >> 8 align = bytes([msb, lsb]) if self.endian == "big" else bytes([lsb, msb]) self.boot_magic = align + bytes([0x2d, 0xe1, 0x5d, 0x29, 0x41, 0x0b, 0x8d, 0x77, 0x67, 0x9c, 0x11, 0x0f, 0x1f, 0x8a, ]) if security_counter == 'auto': # Security counter has not been explicitly provided, # generate it from the version number self.security_counter = ((self.version.major << 24) + (self.version.minor << 16) + self.version.revision) else: self.security_counter = security_counter def __repr__(self): return "".format( self.version, self.header_size, self.security_counter, self.base_addr if self.base_addr is not None else "N/A", self.load_addr, self.align, self.slot_size, self.max_sectors, self.overwrite_only, self.endian, self.__class__.__name__, len(self.payload)) def load(self, path): """Load an image from a given file""" ext = os.path.splitext(path)[1][1:].lower() try: if ext == INTEL_HEX_EXT: ih = IntelHex(path) self.payload = ih.tobinarray() self.base_addr = ih.minaddr() else: with open(path, 'rb') as f: self.payload = f.read() except FileNotFoundError: raise click.UsageError("Input file not found") # Add the image header if needed. if self.pad_header and self.header_size > 0: if self.base_addr: # Adjust base_addr for new header self.base_addr -= self.header_size self.payload = bytes([self.erased_val] * self.header_size) + \ self.payload self.check_header() def save(self, path, hex_addr=None): """Save an image from a given file""" ext = os.path.splitext(path)[1][1:].lower() if ext == INTEL_HEX_EXT: # input was in binary format, but HEX needs to know the base addr if self.base_addr is None and hex_addr is None: raise click.UsageError("No address exists in input file " "neither was it provided by user") h = IntelHex() if hex_addr is not None: self.base_addr = hex_addr h.frombytes(bytes=self.payload, offset=self.base_addr) if self.pad: trailer_size = self._trailer_size(self.align, self.max_sectors, self.overwrite_only, self.enckey, self.save_enctlv, self.enctlv_len) trailer_addr = (self.base_addr + self.slot_size) - trailer_size if self.confirm and not self.overwrite_only: magic_align_size = align_up(len(self.boot_magic), self.max_align) image_ok_idx = -(magic_align_size + self.max_align) flag = bytearray([self.erased_val] * self.max_align) flag[0] = 0x01 # image_ok = 0x01 h.puts(trailer_addr + trailer_size + image_ok_idx, bytes(flag)) h.puts(trailer_addr + (trailer_size - len(self.boot_magic)), bytes(self.boot_magic)) h.tofile(path, 'hex') else: if self.pad: self.pad_to(self.slot_size) with open(path, 'wb') as f: f.write(self.payload) def check_header(self): if self.header_size > 0 and not self.pad_header: if any(v != 0 for v in self.payload[0:self.header_size]): raise click.UsageError("Header padding was not requested and " "image does not start with zeros") def check_trailer(self): if self.slot_size > 0: tsize = self._trailer_size(self.align, self.max_sectors, self.overwrite_only, self.enckey, self.save_enctlv, self.enctlv_len) padding = self.slot_size - (len(self.payload) + tsize) if padding < 0: msg = "Image size (0x{:x}) + trailer (0x{:x}) exceeds " \ "requested size 0x{:x}".format( len(self.payload), tsize, self.slot_size) raise click.UsageError(msg) def ecies_hkdf(self, enckey, plainkey): if isinstance(enckey, ecdsa.ECDSA256P1Public): newpk = ec.generate_private_key(ec.SECP256R1(), default_backend()) shared = newpk.exchange(ec.ECDH(), enckey._get_public()) else: newpk = X25519PrivateKey.generate() shared = newpk.exchange(enckey._get_public()) derived_key = HKDF( algorithm=hashes.SHA256(), length=48, salt=None, info=b'MCUBoot_ECIES_v1', backend=default_backend()).derive(shared) encryptor = Cipher(algorithms.AES(derived_key[:16]), modes.CTR(bytes([0] * 16)), backend=default_backend()).encryptor() cipherkey = encryptor.update(plainkey) + encryptor.finalize() mac = hmac.HMAC(derived_key[16:], hashes.SHA256(), backend=default_backend()) mac.update(cipherkey) ciphermac = mac.finalize() if isinstance(enckey, ecdsa.ECDSA256P1Public): pubk = newpk.public_key().public_bytes( encoding=Encoding.X962, format=PublicFormat.UncompressedPoint) else: pubk = newpk.public_key().public_bytes( encoding=Encoding.Raw, format=PublicFormat.Raw) return cipherkey, ciphermac, pubk def create(self, key, public_key_format, enckey, dependencies=None, sw_type=None, custom_tlvs=None, encrypt_keylen=128, clear=False, fixed_sig=None, pub_key=None, vector_to_sign=None): self.enckey = enckey # Check what hashing algorithm should be used if (key is not None and isinstance(key, ecdsa.ECDSA384P1) or pub_key is not None and isinstance(pub_key, ecdsa.ECDSA384P1Public)): hash_algorithm = hashlib.sha384 hash_tlv = "SHA384" else: hash_algorithm = hashlib.sha256 hash_tlv = "SHA256" # Calculate the hash of the public key if key is not None: pub = key.get_public_bytes() sha = hash_algorithm() sha.update(pub) pubbytes = sha.digest() elif pub_key is not None: if hasattr(pub_key, 'sign'): print(os.path.basename(__file__) + ": sign the payload") pub = pub_key.get_public_bytes() sha = hash_algorithm() sha.update(pub) pubbytes = sha.digest() else: pubbytes = bytes(hashlib.sha256().digest_size) protected_tlv_size = 0 if self.security_counter is not None: # Size of the security counter TLV: header ('HH') + payload ('I') # = 4 + 4 = 8 Bytes protected_tlv_size += TLV_SIZE + 4 if sw_type is not None: if len(sw_type) > MAX_SW_TYPE_LENGTH: msg = "'{}' is too long ({} characters) for sw_type. Its " \ "maximum allowed length is 12 characters.".format( sw_type, len(sw_type)) raise click.UsageError(msg) image_version = (str(self.version.major) + '.' + str(self.version.minor) + '.' + str(self.version.revision)) # The image hash is computed over the image header, the image # itself and the protected TLV area. However, the boot record TLV # (which is part of the protected area) should contain this hash # before it is even calculated. For this reason the script fills # this field with zeros and the bootloader will insert the right # value later. digest = bytes(hash_algorithm().digest_size) # Create CBOR encoded boot record boot_record = create_sw_component_data(sw_type, image_version, hash_tlv, digest, pubbytes) protected_tlv_size += TLV_SIZE + len(boot_record) if dependencies is not None: # Size of a Dependency TLV = Header ('HH') + Payload('IBBHI') # = 4 + 12 = 16 Bytes dependencies_num = len(dependencies[DEP_IMAGES_KEY]) protected_tlv_size += (dependencies_num * 16) if custom_tlvs is not None: for value in custom_tlvs.values(): protected_tlv_size += TLV_SIZE + len(value) if protected_tlv_size != 0: # Add the size of the TLV info header protected_tlv_size += TLV_INFO_SIZE # At this point the image is already on the payload # # This adds the padding if image is not aligned to the 16 Bytes # in encrypted mode if self.enckey is not None: pad_len = len(self.payload) % 16 if pad_len > 0: pad = bytes(16 - pad_len) if isinstance(self.payload, bytes): self.payload += pad else: self.payload.extend(pad) # This adds the header to the payload as well if encrypt_keylen == 256: self.add_header(enckey, protected_tlv_size, 256) else: self.add_header(enckey, protected_tlv_size) prot_tlv = TLV(self.endian, TLV_PROT_INFO_MAGIC) # Protected TLVs must be added first, because they are also included # in the hash calculation protected_tlv_off = None if protected_tlv_size != 0: e = STRUCT_ENDIAN_DICT[self.endian] if self.security_counter is not None: payload = struct.pack(e + 'I', self.security_counter) prot_tlv.add('SEC_CNT', payload) if sw_type is not None: prot_tlv.add('BOOT_RECORD', boot_record) if dependencies is not None: for i in range(dependencies_num): payload = struct.pack( e + 'B3x'+'BBHI', int(dependencies[DEP_IMAGES_KEY][i]), dependencies[DEP_VERSIONS_KEY][i].major, dependencies[DEP_VERSIONS_KEY][i].minor, dependencies[DEP_VERSIONS_KEY][i].revision, dependencies[DEP_VERSIONS_KEY][i].build ) prot_tlv.add('DEPENDENCY', payload) if custom_tlvs is not None: for tag, value in custom_tlvs.items(): prot_tlv.add(tag, value) protected_tlv_off = len(self.payload) self.payload += prot_tlv.get() tlv = TLV(self.endian) # Note that ecdsa wants to do the hashing itself, which means # we get to hash it twice. sha = hash_algorithm() sha.update(self.payload) digest = sha.digest() tlv.add(hash_tlv, digest) if vector_to_sign == 'payload': # Stop amending data to the image # Just keep data vector which is expected to be signed print(os.path.basename(__file__) + ': export payload') return elif vector_to_sign == 'digest': self.payload = digest print(os.path.basename(__file__) + ': export digest') return if key is not None or fixed_sig is not None: if public_key_format == 'hash': tlv.add('KEYHASH', pubbytes) else: tlv.add('PUBKEY', pub) if key is not None and fixed_sig is None: # `sign` expects the full image payload (hashing done # internally), while `sign_digest` expects only the digest # of the payload if hasattr(key, 'sign'): print(os.path.basename(__file__) + ": sign the payload") sig = key.sign(bytes(self.payload)) else: print(os.path.basename(__file__) + ": sign the digest") sig = key.sign_digest(digest) tlv.add(key.sig_tlv(), sig) self.signature = sig elif fixed_sig is not None and key is None: tlv.add(pub_key.sig_tlv(), fixed_sig['value']) self.signature = fixed_sig['value'] else: raise click.UsageError("Can not sign using key and provide fixed-signature at the same time") # At this point the image was hashed + signed, we can remove the # protected TLVs from the payload (will be re-added later) if protected_tlv_off is not None: self.payload = self.payload[:protected_tlv_off] if enckey is not None: if encrypt_keylen == 256: plainkey = os.urandom(32) else: plainkey = os.urandom(16) if isinstance(enckey, rsa.RSAPublic): cipherkey = enckey._get_public().encrypt( plainkey, padding.OAEP( mgf=padding.MGF1(algorithm=hashes.SHA256()), algorithm=hashes.SHA256(), label=None)) self.enctlv_len = len(cipherkey) tlv.add('ENCRSA2048', cipherkey) elif isinstance(enckey, (ecdsa.ECDSA256P1Public, x25519.X25519Public)): cipherkey, mac, pubk = self.ecies_hkdf(enckey, plainkey) enctlv = pubk + mac + cipherkey self.enctlv_len = len(enctlv) if isinstance(enckey, ecdsa.ECDSA256P1Public): tlv.add('ENCEC256', enctlv) else: tlv.add('ENCX25519', enctlv) if not clear: nonce = bytes([0] * 16) cipher = Cipher(algorithms.AES(plainkey), modes.CTR(nonce), backend=default_backend()) encryptor = cipher.encryptor() img = bytes(self.payload[self.header_size:]) self.payload[self.header_size:] = \ encryptor.update(img) + encryptor.finalize() self.payload += prot_tlv.get() self.payload += tlv.get() self.check_trailer() def get_signature(self): return self.signature def add_header(self, enckey, protected_tlv_size, aes_length=128): """Install the image header.""" flags = 0 if enckey is not None: if aes_length == 128: flags |= IMAGE_F['ENCRYPTED_AES128'] else: flags |= IMAGE_F['ENCRYPTED_AES256'] if self.load_addr != 0: # Indicates that this image should be loaded into RAM # 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 magic_align_size = align_up(magic_size, self.max_align) if overwrite_only: return self.max_align * 2 + magic_align_size else: if write_size not in set([1, 2, 4, 8, 16, 32]): 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 = align_up(enctlv_len, self.max_align) else: keylen = align_up(16, self.max_align) trailer += keylen * 2 # encryption keys trailer += self.max_align * 4 # image_ok/copy_done/swap_info/swap_size trailer += magic_align_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(self.boot_magic))) pbytes += self.boot_magic if self.confirm and not self.overwrite_only: magic_size = 16 magic_align_size = align_up(magic_size, self.max_align) image_ok_idx = -(magic_align_size + self.max_align) pbytes[image_ok_idx] = 0x01 # image_ok = 0x01 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 if isinstance(key, ecdsa.ECDSA384P1Public): sha = hashlib.sha384() hash_tlv = "SHA384" else: sha = hashlib.sha256() hash_tlv = "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[hash_tlv]: 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