imgtool: Add support for SUIT signatures
This adds a `--suit` argument to the sign command that will generate a
signed SUIT manifest instead of the TLV style manifest. Currently, this
only supports RSA-2048+SHA256 (RS256), with an unencrypted image.
Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/scripts/imgtool/suit.py b/scripts/imgtool/suit.py
new file mode 100644
index 0000000..90fee88
--- /dev/null
+++ b/scripts/imgtool/suit.py
@@ -0,0 +1,132 @@
+# Copyright 2019 Linaro Limited
+#
+# 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.
+
+"""
+SUIT Image signing and management.
+"""
+
+from . import image
+import cbor2
+import hashlib
+import os.path
+import struct
+
+IMAGE_MAGIC = 0x96f3b83e
+IMAGE_HEADER_SIZE = 32
+BIN_EXT = "bin"
+INTEL_HEX_EXT = "hex"
+DEFAULT_MAX_SECTORS = 128
+
+MANIFEST_INFO_SIZE = 4
+MANIFEST_INFO_MAGIC = 0x6917
+
+STRUCT_ENDIAN_DICT = {
+ 'little': '<',
+ 'big:': '>'
+}
+
+class Suit():
+
+ def __init__(self, endian):
+ self.payload = None
+ self.sequence = 0
+ self.endian = endian
+
+ def add_payload(self, payload):
+ self.payload = payload
+
+ def set_sequence(self, sequence):
+ self.sequence = sequence
+
+ def generate(self, key):
+ manifest = self._gen_manifest(self.payload)
+ sig = self._gen_sig(manifest, key)
+
+ body = cbor2.dumps({1: sig, 2: manifest})
+
+ return (struct.pack(STRUCT_ENDIAN_DICT[self.endian] +
+ "HH", MANIFEST_INFO_MAGIC, MANIFEST_INFO_SIZE + len(body)) +
+ body)
+
+ def _get_digest(self, payload, prot):
+ """Make a COSE Digest of the payload, with the given
+ CBOR-encoded protected data. This is defined by SUIT."""
+ block = cbor2.dumps(["Digest", prot, payload])
+ sha = hashlib.sha256()
+ sha.update(block)
+ digest = sha.digest()
+
+ return [prot, {}, None, digest]
+
+ def _gen_manifest(self, payload):
+ """Generate the actual SUIT manifest itself."""
+ prot = cbor2.dumps({1: 41})
+ digest = self._get_digest(payload, prot)
+
+ return cbor2.dumps({
+ 1: 1,
+ 2: self.sequence,
+ 3: [ { 1: [b"0"], 2: len(payload), 3: digest } ] })
+
+ def _gen_sig(self, body, key):
+ """Generate a COSE signature wrapper for the given payload,
+ signed with the given key. This doesn't return CBOR, but a
+ Python data structure intended to be included within CBOR."""
+ body_prot = cbor2.dumps({3: 0})
+ sig_prot = cbor2.dumps({1: -37}) # TODO: Hardcoded, -37 is RS256.
+
+ # The block we actually sign.
+ sig_block = cbor2.dumps(["Signature", body_prot, sig_prot, b"", body])
+
+ sig = key.sign(bytes(sig_block))
+
+ return cbor2.CBORTag(98, [body_prot, {}, None, [
+ [sig_prot, {4: b"key-id-here"}, sig]]])
+
+class Image(image.Image):
+
+ def __init__(self, **kwargs):
+ image.Image.__init__(self, **kwargs)
+
+ 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")
+ if self.slot_size > 0:
+ tsize = self._trailer_size(self.align, self.max_sectors,
+ self.overwrite_only)
+ 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 Exception(msg)
+
+ def create(self, key, enckey):
+ if enckey is not None:
+ raise Exception("SUIT support does not yet support encryption")
+
+ self.add_header(None)
+
+ s = Suit(self.endian)
+ s.add_payload(self.payload)
+ # TODO: Where does this sequence number come from?
+ s.set_sequence(self.version.build)
+
+ self.payload += s.generate(key)
+
+ def _image_magic(self):
+ return IMAGE_MAGIC