From f464cf830a3f50ab5cb1ccdd38ec411c9e6858ed Mon Sep 17 00:00:00 2001
From: kYc0o <fco.ja.ac@gmail.com>
Date: Fri, 9 Jun 2017 17:53:06 +0200
Subject: [PATCH] dist/tools: add imgtool
---
dist/tools/mcuboot/imgtool.md | 89 +++++++++++++
dist/tools/mcuboot/imgtool.py | 100 ++++++++++++++
dist/tools/mcuboot/imgtool/__init__.py | 0
dist/tools/mcuboot/imgtool/image.py | 172 +++++++++++++++++++++++++
dist/tools/mcuboot/imgtool/keys.py | 137 ++++++++++++++++++++
dist/tools/mcuboot/imgtool/version.py | 33 +++++
6 files changed, 531 insertions(+)
create mode 100644 dist/tools/mcuboot/imgtool.md
create mode 100755 dist/tools/mcuboot/imgtool.py
create mode 100644 dist/tools/mcuboot/imgtool/__init__.py
create mode 100644 dist/tools/mcuboot/imgtool/image.py
create mode 100644 dist/tools/mcuboot/imgtool/keys.py
create mode 100644 dist/tools/mcuboot/imgtool/version.py
diff --git a/dist/tools/mcuboot/imgtool.md b/dist/tools/mcuboot/imgtool.md
new file mode 100644
index 0000000000..38f81247e6
--- /dev/null
+++ b/dist/tools/mcuboot/imgtool.md
@@ -0,0 +1,89 @@
+## Image tool
+
+The Python program `imgtool.py` can be used to perform the
+operations that are necessary to manage keys and sign images.
+
+This program is written for Python3, and has several dependencies on
+Python libraries. These can be installed using 'pip3' manually:
+
+ pip3 install --user pycrypto
+ pip3 install --user pyasn1
+ pip3 install --user ecdsa
+
+or, on Ubuntu, using the package manager:
+
+ sudo apt-get install python3-crypto python3-pyasn1 python3-ecdsa
+
+## Managing keys
+
+This tool currently supports rsa-2048 and ecdsa-p256 keys. You can
+generate a keypair for one of these types using the 'keygen' command:
+
+ ./imgtool.py keygen -k filename.pem -t rsa-2048
+
+or use ecdsa-p256 for the type. The key type used should match what
+mcuboot is configured to verify.
+
+This key file is what is used to sign images, this file should be
+protected, and not widely distributed.
+
+## Incorporating the public key into the code
+
+There is a development key distributed with mcuboot that can be used
+for testing. Since this private key is widely distributed, it should
+never be used for production. Once you have generated a production
+key, as described above, you should replace the public key in the
+bootloader with the generated one.
+
+For Zephyr, the keys live in the file `boot/zephyr/keys.c`. For
+mynewt, follow the instructions in `doc/signed_images.md` to generate
+the key file.
+
+ ./imgtool.py getpub -k filename.pem
+
+will extract the public key from the given private key file, and
+output it as a C data structure. You can replace or insert this code
+into the key file.
+
+## Signing images
+
+Image signing takes a binary image intended for Slot 0 and adds a
+header and trailer that the bootloader is expecting:
+
+ usage: imgtool.py sign [-h] -k filename --align ALIGN -v VERSION -H
+ HEADER_SIZE [--pad PAD] [--rsa-pkcs1-15]
+ infile outfile
+
+ positional arguments:
+ infile
+ outfile
+
+ optional arguments:
+ -h, --help show this help message and exit
+ -k filename, --key filename
+ --align ALIGN
+ -v VERSION, --version VERSION
+ -H HEADER_SIZE, --header-size HEADER_SIZE
+ --included-header Image has gap for header
+ --pad PAD Pad image to this many bytes, adding trailer magic
+ --rsa-pkcs1-15 Use old PKCS#1 v1.5 signature algorithm
+
+The main arguments given are the key file generated above, a version
+field to place in the header (1.2.3 for example), the alignment of the
+flash device in question, and the header size.
+
+The header size depends on the operating system and the particular
+flash device. For Zephyr, it will be configured as part of the build,
+and will be a small power of two. By default, the header will be
+prepended to the image. If `--included-header` is given, the image
+must start with header-size bytes of zeros, and the header will be
+overwritten over these bytes.
+
+The optional --pad argument will place a trailer on the image that
+indicates that the image should be considered an upgrade. Writing
+this image in slot 1 will then cause the bootloader to upgrade to it.
+
+Lastly, the --rsa-pkcs1-15 will cause the tool to use the older,
+deprecated pkcs#1 v1.5 signing algorithm when using RSA. This can be
+enabled in the bootloader as well, and may be needed if you are using
+an older version of the bootloader.
diff --git a/dist/tools/mcuboot/imgtool.py b/dist/tools/mcuboot/imgtool.py
new file mode 100755
index 0000000000..6bc3cd0597
--- /dev/null
+++ b/dist/tools/mcuboot/imgtool.py
@@ -0,0 +1,100 @@
+#! /usr/bin/env python3
+
+import argparse
+from imgtool import keys
+from imgtool import image
+from imgtool import version
+import sys
+
+def gen_rsa2048(args):
+ keys.RSA2048.generate().export_private(args.key)
+def gen_ecdsa_p256(args):
+ keys.ecdsa256p1.generate().export_private(args.key)
+def gen_ecdsa_p224(args):
+ print("TODO: p-224 not yet implemented")
+
+keygens = {
+ 'rsa-2048': gen_rsa2048,
+ 'ecdsa-p256': gen_ecdsa_p256,
+ 'ecdsa-p224': gen_ecdsa_p224, }
+
+def do_keygen(args):
+ if args.type not in keygens:
+ msg = "Unexpected key type: {}".format(args.type)
+ raise argparse.ArgumentTypeError(msg)
+ keygens[args.type](args)
+
+def do_getpub(args):
+ key = keys.load(args.key)
+ key.emit_c()
+
+def do_sign(args):
+ align = args.align
+ if args.rsa_pkcs1_15:
+ keys.sign_rsa_pss = False
+ img = image.Image.load(args.infile, version=args.version,
+ header_size=args.header_size,
+ included_header=args.included_header,
+ pad=args.pad)
+ key = keys.load(args.key) if args.key else None
+ img.sign(key)
+
+ if args.pad:
+ img.pad_to(args.pad, args.align)
+
+ img.save(args.outfile)
+
+subcmds = {
+ 'keygen': do_keygen,
+ 'getpub': do_getpub,
+ 'sign': do_sign, }
+
+def alignment_value(text):
+ value = int(text)
+ if value not in [1, 2, 4, 8]:
+ msg = "{} must be one of 1, 2, 4 or 8".format(value)
+ raise argparse.ArgumentTypeError(msg)
+ return value
+
+def intparse(text):
+ """Parse a command line argument as an integer.
+
+ Accepts 0x and other prefixes to allow other bases to be used."""
+ return int(text, 0)
+
+def args():
+ parser = argparse.ArgumentParser()
+ subs = parser.add_subparsers(help='subcommand help', dest='subcmd')
+
+ keygenp = subs.add_parser('keygen', help='Generate pub/private keypair')
+ keygenp.add_argument('-k', '--key', metavar='filename', required=True)
+ keygenp.add_argument('-t', '--type', metavar='type',
+ choices=['rsa-2048', 'ecdsa-p224', 'ecdsa-p256'],
+ required=True)
+
+ getpub = subs.add_parser('getpub', help='Get public key from keypair')
+ getpub.add_argument('-k', '--key', metavar='filename', required=True)
+
+ sign = subs.add_parser('sign', help='Sign an image with a private key')
+ sign.add_argument('-k', '--key', metavar='filename')
+ sign.add_argument("--align", type=alignment_value, required=True)
+ sign.add_argument("-v", "--version", type=version.decode_version, required=True)
+ sign.add_argument("-H", "--header-size", type=intparse, required=True)
+ sign.add_argument("--included-header", default=False, action='store_true',
+ help='Image has gap for header')
+ sign.add_argument("--pad", type=intparse,
+ help='Pad image to this many bytes, adding trailer magic')
+ sign.add_argument("--rsa-pkcs1-15", help='Use old PKCS#1 v1.5 signature algorithm',
+ default=False, action='store_true')
+ sign.add_argument("infile")
+ sign.add_argument("outfile")
+
+ args = parser.parse_args()
+ if args.subcmd is None:
+ print('Must specify a subcommand', file=sys.stderr)
+ sys.exit(1)
+
+ subcmds[args.subcmd](args)
+
+if __name__ == '__main__':
+ args()
diff --git a/dist/tools/mcuboot/imgtool/__init__.py b/dist/tools/mcuboot/imgtool/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/dist/tools/mcuboot/imgtool/image.py b/dist/tools/mcuboot/imgtool/image.py
new file mode 100644
index 0000000000..49b82492f0
--- /dev/null
+++ b/dist/tools/mcuboot/imgtool/image.py
@@ -0,0 +1,172 @@
+"""
+Image signing and management.
+"""
+
+from . import version as versmod
+import hashlib
+import struct
+
+IMAGE_MAGIC = 0x96f3b83c
+IMAGE_HEADER_SIZE = 32
+
+# Image header flags.
+IMAGE_F = {
+ 'PIC': 0x0000001,
+ 'SHA256': 0x0000002,
+ 'PKCS15_RSA2048_SHA256': 0x0000004,
+ 'ECDSA224_SHA256': 0x0000008,
+ 'NON_BOOTABLE': 0x0000010,
+ 'ECDSA256_SHA256': 0x0000020,
+ 'PKCS1_PSS_RSA2048_SHA256': 0x0000040, }
+
+TLV_VALUES = {
+ 'SHA256': 1,
+ 'RSA2048': 2,
+ 'ECDSA224': 3,
+ 'ECDSA256': 4, }
+
+TLV_HEADER_SIZE = 4
+
+# Sizes of the image trailer, depending on image alignment.
+trailer_sizes = {
+ 1: 402,
+ 2: 788,
+ 4: 1560,
+ 8: 3104, }
+
+boot_magic = bytes([
+ 0x77, 0xc2, 0x95, 0xf3,
+ 0x60, 0xd2, 0xef, 0x7f,
+ 0x35, 0x52, 0x50, 0x0f,
+ 0x2c, 0xb6, 0x79, 0x80, ])
+
+class TLV():
+ def __init__(self):
+ self.buf = bytearray()
+
+ def add(self, kind, payload):
+ """Add a TLV record. Kind should be a string found in TLV_VALUES above."""
+ buf = struct.pack('<BBH', TLV_VALUES[kind], 0, len(payload))
+ self.buf += buf
+ self.buf += payload
+
+ def get(self):
+ return bytes(self.buf)
+
+class Image():
+ @classmethod
+ def load(cls, path, included_header=False, **kwargs):
+ """Load an image from a given file"""
+ with open(path, 'rb') as f:
+ payload = f.read()
+ obj = cls(**kwargs)
+ obj.payload = payload
+
+ # Add the image header if needed.
+ if not included_header and obj.header_size > 0:
+ obj.payload = (b'\000' * obj.header_size) + obj.payload
+
+ obj.check()
+ return obj
+
+ def __init__(self, version=None, header_size=IMAGE_HEADER_SIZE, pad=0):
+ self.version = version or versmod.decode_version("0")
+ self.header_size = header_size or IMAGE_HEADER_SIZE
+ self.pad = pad
+
+ def __repr__(self):
+ return "<Image version={}, header_size={}, pad={}, payloadlen=0x{:x}>".format(
+ self.version,
+ self.header_size,
+ self.pad,
+ len(self.payload))
+
+ def save(self, path):
+ with open(path, 'wb') as f:
+ f.write(self.payload)
+
+ def check(self):
+ """Perform some sanity checking of the image."""
+ # If there is a header requested, make sure that the image
+ # starts with all zeros.
+ if self.header_size > 0:
+ if any(v != 0 for v in self.payload[0:self.header_size]):
+ raise Exception("Padding requested, but image does not start with zeros")
+
+ def sign(self, key):
+ self.add_header(key)
+
+ tlv = TLV()
+
+ # Note that ecdsa wants to do the hashing itself, which means
+ # we get to hash it twice.
+ sha = hashlib.sha256()
+ sha.update(self.payload)
+ digest = sha.digest()
+
+ tlv.add('SHA256', digest)
+
+ if key is not None:
+ sig = key.sign(self.payload)
+ tlv.add(key.sig_tlv(), sig)
+
+ self.payload += tlv.get()
+
+ def add_header(self, key):
+ """Install the image header.
+
+ The key is needed to know the type of signature, and
+ approximate the size of the signature."""
+
+ flags = 0
+ tlvsz = 0
+ if key is not None:
+ flags |= IMAGE_F[key.sig_type()]
+ tlvsz += TLV_HEADER_SIZE + key.sig_len()
+
+ flags |= IMAGE_F['SHA256']
+ tlvsz += 4 + hashlib.sha256().digest_size
+
+ fmt = ('<' +
+ # type ImageHdr struct {
+ 'I' + # Magic uint32
+ 'H' + # TlvSz uint16
+ 'B' + # KeyId uint8
+ 'B' + # Pad1 uint8
+ 'H' + # HdrSz uint16
+ 'H' + # Pad2 uint16
+ 'I' + # ImgSz uint32
+ 'I' + # Flags uint32
+ 'BBHI' + # Vers ImageVersion
+ 'I' # Pad3 uint32
+ ) # }
+ assert struct.calcsize(fmt) == IMAGE_HEADER_SIZE
+ header = struct.pack(fmt,
+ IMAGE_MAGIC,
+ tlvsz, # TlvSz
+ 0, # KeyId (TODO: allow other ids)
+ 0, # Pad1
+ self.header_size,
+ 0, # Pad2
+ len(self.payload) - self.header_size, # ImageSz
+ flags, # Flags
+ self.version.major,
+ self.version.minor or 0,
+ self.version.revision or 0,
+ self.version.build or 0,
+ 0) # Pad3
+ self.payload = bytearray(self.payload)
+ self.payload[:len(header)] = header
+
+ def pad_to(self, size, align):
+ """Pad the image to the given size, with the given flash alignment."""
+ tsize = trailer_sizes[align]
+ padding = 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, size)
+ raise Exception(msg)
+ pbytes = b'\xff' * padding
+ pbytes += boot_magic
+ pbytes += b'\xff' * (tsize - len(boot_magic))
+ self.payload += pbytes
diff --git a/dist/tools/mcuboot/imgtool/keys.py b/dist/tools/mcuboot/imgtool/keys.py
new file mode 100644
index 0000000000..fc90f9e06a
--- /dev/null
+++ b/dist/tools/mcuboot/imgtool/keys.py
@@ -0,0 +1,137 @@
+"""
+Cryptographic key management for imgtool.
+"""
+
+from Crypto.Hash import SHA256
+from Crypto.PublicKey import RSA
+from Crypto.Signature import PKCS1_v1_5, PKCS1_PSS
+from ecdsa import SigningKey, NIST256p, util
+import hashlib
+from pyasn1.type import namedtype, univ
+from pyasn1.codec.der.encoder import encode
+
+# By default, we use RSA-PSS (PKCS 2.1). That can be overridden on
+# the command line to support the older (less secure) PKCS1.5
+sign_rsa_pss = True
+
+AUTOGEN_MESSAGE = "/* Autogenerated by imgtool.py, do not edit. */"
+
+class RSAPublicKey(univ.Sequence):
+ componentType = namedtype.NamedTypes(
+ namedtype.NamedType('modulus', univ.Integer()),
+ namedtype.NamedType('publicExponent', univ.Integer()))
+
+class RSA2048():
+ def __init__(self, key):
+ """Construct an RSA2048 key with the given key data"""
+ self.key = key
+
+ @staticmethod
+ def generate():
+ return RSA2048(RSA.generate(2048))
+
+ def export_private(self, path):
+ with open(path, 'wb') as f:
+ f.write(self.key.exportKey('PEM'))
+
+ def emit_c(self):
+ node = RSAPublicKey()
+ node['modulus'] = self.key.n
+ node['publicExponent'] = self.key.e
+ print(AUTOGEN_MESSAGE)
+ print("const unsigned char rsa_pub_key[] = {", end='')
+ encoded = bytearray(encode(node))
+ for count, b in enumerate(encoded):
+ if count % 8 == 0:
+ print("\n\t", end='')
+ else:
+ print(" ", end='')
+ print("0x{:02x},".format(b), end='')
+ print("\n};")
+ print("const unsigned int rsa_pub_key_len = {};".format(len(encoded)))
+
+ def sig_type(self):
+ """Return the type of this signature (as a string)"""
+ if sign_rsa_pss:
+ return "PKCS1_PSS_RSA2048_SHA256"
+ else:
+ return "PKCS15_RSA2048_SHA256"
+
+ def sig_len(self):
+ return 256
+
+ def sig_tlv(self):
+ return "RSA2048"
+
+ def sign(self, payload):
+ sha = SHA256.new(payload)
+ if sign_rsa_pss:
+ signer = PKCS1_PSS.new(self.key)
+ else:
+ signer = PKCS1_v1_5.new(self.key)
+ signature = signer.sign(sha)
+ assert len(signature) == self.sig_len()
+ return signature
+
+class ECDSA256P1():
+ def __init__(self, key):
+ """Construct an ECDSA P-256 private key"""
+ self.key = key
+
+ @staticmethod
+ def generate():
+ return ECDSA256P1(SigningKey.generate(curve=NIST256p))
+
+ def export_private(self, path):
+ with open(path, 'wb') as f:
+ f.write(key.to_pem())
+
+ def emit_c(self):
+ vk = self.key.get_verifying_key()
+ print(AUTOGEN_MESSAGE)
+ print("const unsigned char ecdsa_pub_key[] = {", end='')
+ encoded = bytes(vk.to_der())
+ for count, b in enumerate(encoded):
+ if count % 8 == 0:
+ print("\n\t", end='')
+ else:
+ print(" ", end='')
+ print("0x{:02x},".format(b), end='')
+ print("\n};")
+ print("const unsigned int ecdsa_pub_key_len = {};".format(len(encoded)))
+
+ def sign(self, payload):
+ # To make this fixed length, possibly pad with zeros.
+ sig = self.key.sign(payload, hashfunc=hashlib.sha256, sigencode=util.sigencode_der)
+ sig += b'\000' * (self.sig_len() - len(sig))
+ return sig
+
+ def sig_len(self):
+ # The DER encoding depends on the high bit, and can be
+ # anywhere from 70 to 72 bytes. Because we have to fill in
+ # the length field before computing the signature, however,
+ # we'll give the largest, and the sig checking code will allow
+ # for it to be up to two bytes larger than the actual
+ # signature.
+ return 72
+
+ def sig_type(self):
+ """Return the type of this signature (as a string)"""
+ return "ECDSA256_SHA256"
+
+ def sig_tlv(self):
+ return "ECDSA256"
+
+def load(path):
+ with open(path, 'rb') as f:
+ pem = f.read()
+ try:
+ key = RSA.importKey(pem)
+ if key.n.bit_length() != 2048:
+ raise Exception("Unsupported RSA bit length, only 2048 supported")
+ return RSA2048(key)
+ except ValueError:
+ key = SigningKey.from_pem(pem)
+ if key.curve.name != 'NIST256p':
+ raise Exception("Unsupported ECDSA curve")
+ return ECDSA256P1(key)
diff --git a/dist/tools/mcuboot/imgtool/version.py b/dist/tools/mcuboot/imgtool/version.py
new file mode 100644
index 0000000000..218f8a822b
--- /dev/null
+++ b/dist/tools/mcuboot/imgtool/version.py
@@ -0,0 +1,33 @@
+"""
+Semi Semantic Versioning
+
+Implements a subset of semantic versioning that is supportable by the image header.
+"""
+
+import argparse
+from collections import namedtuple
+import re
+
+SemiSemVersion = namedtuple('SemiSemVersion', ['major', 'minor', 'revision', 'build'])
+
+version_re = re.compile(r"""^([1-9]\d*|0)(\.([1-9]\d*|0)(\.([1-9]\d*|0)(\+([1-9]\d*|0))?)?)?$""")
+def decode_version(text):
+ """Decode the version string, which should be of the form maj.min.rev+build"""
+ m = version_re.match(text)
+ # print("decode:", text, m.groups())
+ if m:
+ result = SemiSemVersion(
+ int(m.group(1)) if m.group(1) else 0,
+ int(m.group(3)) if m.group(3) else 0,
+ int(m.group(5)) if m.group(5) else 0,
+ int(m.group(7)) if m.group(7) else 0)
+ return result
+ else:
+ msg = "Invalid version number, should be maj.min.rev+build with later parts optional"
+ raise argparse.ArgumentTypeError(msg)
+
+if __name__ == '__main__':
+ print(decode_version("1.2"))
+ print(decode_version("1.0"))
+ print(decode_version("0.0.2+75"))
+ print(decode_version("0.0.0+00"))
--
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