115 lines
3.7 KiB
Python
115 lines
3.7 KiB
Python
# Copyright 2017 Linaro Limited
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# Copyright (c) 2017-2019, Arm Limited.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""
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Cryptographic key management for imgtool.
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"""
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from __future__ import print_function
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from Crypto.Hash import SHA256
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from Crypto.PublicKey import RSA
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from Crypto.Signature import PKCS1_v1_5, PKCS1_PSS
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import hashlib
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from pyasn1.type import namedtype, univ
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from pyasn1.codec.der.encoder import encode
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# Sizes that bootutil will recognize
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RSA_KEY_SIZES = [2048, 3072]
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# By default, we use RSA-PSS (PKCS 2.1). That can be overridden on
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# the command line to support the older (less secure) PKCS1.5
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sign_rsa_pss = True
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AUTOGEN_MESSAGE = "/* Autogenerated by imgtool.py, do not edit. */"
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class RSAUsageError(Exception):
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pass
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class RSAPublicKey(univ.Sequence):
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componentType = namedtype.NamedTypes(
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namedtype.NamedType('modulus', univ.Integer()),
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namedtype.NamedType('publicExponent', univ.Integer()))
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class RSAutil():
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def __init__(self, key):
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"""Construct an RSA key with the given key data"""
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self.key = key
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def key_size(self):
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return self.key.n.bit_length()
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@staticmethod
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def generate(key_size=2048):
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if key_size not in RSA_KEY_SIZES:
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raise RSAUsageError("Key size {} is not supported by MCUboot"
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.format(key_size))
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return RSAutil(RSA.generate(key_size))
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def export_private(self, path):
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with open(path, 'wb') as f:
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f.write(self.key.exportKey('PEM'))
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def get_public_bytes(self):
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node = RSAPublicKey()
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node['modulus'] = self.key.n
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node['publicExponent'] = self.key.e
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return bytearray(encode(node))
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def emit_c(self):
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print(AUTOGEN_MESSAGE)
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print("const unsigned char rsa_pub_key[] = {", end='')
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encoded = self.get_public_bytes()
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for count, b in enumerate(encoded):
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if count % 8 == 0:
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print("\n\t", end='')
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else:
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print(" ", end='')
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print("0x{:02x},".format(b), end='')
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print("\n};")
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print("const unsigned int rsa_pub_key_len = {};".format(len(encoded)))
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def sig_type(self):
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"""Return the type of this signature (as a string)"""
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if sign_rsa_pss:
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return "PKCS1_PSS_RSA{}_SHA256".format(self.key_size())
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else:
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return "PKCS15_RSA{}_SHA256".format(self.key_size())
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def sig_len(self):
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return 256 if self.key_size() == 2048 else 384
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def sig_tlv(self):
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return "RSA2048" if self.key_size() == 2048 else "RSA3072"
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def sign(self, payload):
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converted_payload = bytes(payload)
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sha = SHA256.new(converted_payload)
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if sign_rsa_pss:
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signer = PKCS1_PSS.new(self.key)
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else:
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signer = PKCS1_v1_5.new(self.key)
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signature = signer.sign(sha)
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assert len(signature) == self.sig_len()
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return signature
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def load(path):
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with open(path, 'rb') as f:
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pem = f.read()
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try:
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key = RSA.importKey(pem)
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return RSAutil(key)
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except ValueError:
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raise Exception("Unsupported RSA key file")
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