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March 18, 2018 10:17
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#!/usr/bin/python3 | |
# -*- coding: utf-8 -*- | |
# ---------------------------------------------------------------------------- | |
# Copyright 2018 ARM Limited or its affiliates | |
# | |
# 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. | |
# ---------------------------------------------------------------------------- | |
""" | |
This is a demo script that is intended to act as a reference for SUIT manifest | |
signing. | |
NOTE: It is expected that C and C++ parser implementations will be written | |
against this script, so it does not adhere to PEP8 in order to maintain | |
similarity between the naming in this script and that of C/C++ implementations. | |
""" | |
import cbor | |
import sys | |
from cryptography.hazmat.backends import default_backend | |
from cryptography.hazmat.primitives import hashes | |
from cryptography.hazmat.primitives.asymmetric import ec | |
from cryptography.hazmat.primitives import serialization | |
# Private key in arg 1 | |
# Public key in arg 2 | |
# Input file in arg 3 | |
# Output file in arg 4 | |
COSE_Sign_Tag = 18 | |
APPLICATION_OCTET_STREAM_ID = 42 | |
ES256 = -7 | |
private_key = None | |
with open(sys.argv[1], 'rb') as fd: | |
private_key = serialization.load_pem_private_key(fd.read(), password=None, backend=default_backend()) | |
public_key = None | |
with open(sys.argv[2], 'rb') as fd: | |
public_key = serialization.load_pem_public_key(fd.read(), backend=default_backend()) | |
# Read the input file | |
doc = None | |
with open(sys.argv[3], 'rb') as fd: | |
doc = fd.read() | |
# Check if the content is already a COSE_Sign_Tagged | |
isCOSE_Sign_Tagged = False | |
COSE_Sign = [] | |
try: | |
decodedDoc = cbor.loads(doc) | |
if isinstance(decodedDoc, cbor.Tag) and decodedDoc.tag == COSE_Sign_Tag: | |
isCOSE_Sign_Tagged = True | |
COSE_Sign = decodedDoc.value | |
except: | |
pass | |
if not isCOSE_Sign_Tagged: | |
protected = cbor.dumps({ | |
3: APPLICATION_OCTET_STREAM_ID, # Content Type | |
}) | |
unprotected = { | |
} | |
payload = doc | |
signatures = [] | |
# Create a COSE_Sign_Tagged object | |
COSE_Sign = [ | |
protected, | |
unprotected, | |
payload, | |
signatures | |
] | |
# NOTE: Using RFC7093, Method 4 | |
digest = hashes.Hash(hashes.SHA256(), backend=default_backend()) | |
digest.update( | |
public_key.public_bytes(serialization.Encoding.DER, | |
serialization.PublicFormat.SubjectPublicKeyInfo)) | |
kid = digest.finalize() | |
# Sign the payload | |
protected = cbor.dumps({ | |
1: ES256, # alg | |
4: kid #kid | |
}) | |
unprotected = { | |
} | |
Sig_structure = [ | |
"Signature1", # Context | |
COSE_Sign[0], # Body Protected | |
protected, # signature protected | |
b'', # External AAD | |
COSE_Sign[2] | |
] | |
sig_str = cbor.dumps(Sig_structure) | |
signature = private_key.sign( | |
sig_str, | |
ec.ECDSA(hashes.SHA256()) | |
) | |
COSE_Signature = [ | |
protected, | |
unprotected, | |
signature | |
] | |
COSE_Signature2 = signature | |
COSE_Sign[3].append(COSE_Signature2) | |
with open(sys.argv[4], 'wb') as fd: | |
COSE_Sign_Tagged = cbor.Tag(18, COSE_Sign) | |
fd.write(cbor.dumps(COSE_Sign_Tagged)) |
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