scripts: Initial version of Python imgtool
This is the start of a python implementation of imgtool. This
implements all of the functionality that was missing in the zep2newt.py
tool, namely creation of keypairs, and converting the public version of
these keys into C code.
diff --git a/scripts/imgtool/__init__.py b/scripts/imgtool/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/scripts/imgtool/__init__.py
diff --git a/scripts/imgtool/image.py b/scripts/imgtool/image.py
new file mode 100644
index 0000000..10b2d25
--- /dev/null
+++ b/scripts/imgtool/image.py
@@ -0,0 +1,163 @@
+"""
+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, }
+
+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, **kwargs):
+ """Load an image from a given file"""
+ with open(path, 'rb') as f:
+ payload = f.read()
+ obj = cls(**kwargs)
+ obj.payload = 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)
+
+ 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 = IMAGE_F[key.sig_type()]
+ tlvsz = 0
+ 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/scripts/imgtool/keys.py b/scripts/imgtool/keys.py
new file mode 100644
index 0000000..d529b59
--- /dev/null
+++ b/scripts/imgtool/keys.py
@@ -0,0 +1,126 @@
+"""
+Cryptographic key management for imgtool.
+"""
+
+from Crypto.Hash import SHA256
+from Crypto.PublicKey import RSA
+from Crypto.Signature import PKCS1_v1_5
+from ecdsa import SigningKey, NIST256p, util
+from pyasn1.type import namedtype, univ
+from pyasn1.codec.der.encoder import encode
+
+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)"""
+ return "PKCS15_RSA2048_SHA256"
+
+ def sig_len(self):
+ return 256
+
+ def sig_tlv(self):
+ return "RSA2048"
+
+ def sign(self, payload):
+ sha = SHA256.new(payload)
+ 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/scripts/imgtool/version.py b/scripts/imgtool/version.py
new file mode 100644
index 0000000..eac3667
--- /dev/null
+++ b/scripts/imgtool/version.py
@@ -0,0 +1,27 @@
+"""
+Semi Semantic Versioning
+
+Implements a subset of semantic versioning that is supportable by the image header.
+"""
+
+from collections import namedtuple
+import re
+
+SemiSemVersion = namedtuple('SemiSemVersion', ['major', 'minor', 'revision', 'build'])
+
+version_re = re.compile(r"""^([1-9]\d*)(\.([1-9]\d*)(\.([1-9]\d*)(\+([a-z1-9-][a-z0-9-]*))?)?)?$""")
+def decode_version(text):
+ """Decode the version string, which should be of the form maj.min.rev+build"""
+ # print("decode:", text)
+ m = version_re.match(text)
+ 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)
+