circuitpython/tools/gen_crt_bundle.py

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#!/usr/bin/env python
#
# ESP32 x509 certificate bundle generation utility
#
# Converts PEM and DER certificates to a custom bundle format which stores just the
# subject name and public key to reduce space
#
# The bundle will have the format: number of certificates; crt 1 subject name length; crt 1 public key length;
# crt 1 subject name; crt 1 public key; crt 2...
#
# Copyright 2018-2019 Espressif Systems (Shanghai) PTE LTD
#
# 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
#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
# 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.
from __future__ import with_statement
import argparse
import csv
import os
import re
import struct
import sys
import textwrap
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from io import open
try:
from cryptography import x509
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization
except ImportError:
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print(
"The cryptography package is not installed."
"Please refer to the Get Started section of the ESP-IDF Programming Guide for "
"setting up the required packages."
)
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raise
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ca_bundle_bin_file = "x509_crt_bundle"
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quiet = False
def status(msg):
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"""Print status message to stderr"""
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if not quiet:
critical(msg)
def critical(msg):
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"""Print critical message to stderr"""
sys.stderr.write("gen_crt_bundle.py: ")
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sys.stderr.write(msg)
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sys.stderr.write("\n")
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class CertificateBundle:
def __init__(self):
self.certificates = []
self.compressed_crts = []
if os.path.isfile(ca_bundle_bin_file):
os.remove(ca_bundle_bin_file)
def add_from_path(self, crts_path):
found = False
for file_path in os.listdir(crts_path):
found |= self.add_from_file(os.path.join(crts_path, file_path))
if found is False:
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raise InputError("No valid x509 certificates found in %s" % crts_path)
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def add_from_file(self, file_path):
try:
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if file_path.endswith(".pem"):
status("Parsing certificates from %s" % file_path)
with open(file_path, "r", encoding="utf-8") as f:
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crt_str = f.read()
self.add_from_pem(crt_str)
return True
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elif file_path.endswith(".der"):
status("Parsing certificates from %s" % file_path)
with open(file_path, "rb") as f:
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crt_str = f.read()
self.add_from_der(crt_str)
return True
except ValueError:
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critical("Invalid certificate in %s" % file_path)
raise InputError("Invalid certificate")
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return False
def add_from_pem(self, crt_str):
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"""A single PEM file may have multiple certificates"""
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crt = ""
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count = 0
start = False
for strg in crt_str.splitlines(True):
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if strg == "-----BEGIN CERTIFICATE-----\n" and start is False:
crt = ""
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start = True
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elif strg == "-----END CERTIFICATE-----\n" and start is True:
crt += strg + "\n"
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start = False
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self.certificates.append(
x509.load_pem_x509_certificate(crt.encode(), default_backend())
)
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count += 1
if start is True:
crt += strg
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if count == 0:
raise InputError("No certificate found")
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status("Successfully added %d certificates" % count)
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def add_from_der(self, crt_str):
self.certificates.append(x509.load_der_x509_certificate(crt_str, default_backend()))
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status("Successfully added 1 certificate")
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def create_bundle(self):
# Sort certificates in order to do binary search when looking up certificates
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self.certificates = sorted(
self.certificates, key=lambda cert: cert.subject.public_bytes(default_backend())
)
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bundle = struct.pack(">H", len(self.certificates))
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for crt in self.certificates:
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"""Read the public key as DER format"""
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pub_key = crt.public_key()
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pub_key_der = pub_key.public_bytes(
serialization.Encoding.DER, serialization.PublicFormat.SubjectPublicKeyInfo
)
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""" Read the subject name as DER format """
sub_name_der = crt.subject.public_bytes(default_backend())
name_len = len(sub_name_der)
key_len = len(pub_key_der)
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len_data = struct.pack(">HH", name_len, key_len)
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bundle += len_data
bundle += sub_name_der
bundle += pub_key_der
return bundle
def add_with_filter(self, crts_path, filter_path):
filter_set = set()
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with open(filter_path, "r", encoding="utf-8") as f:
csv_reader = csv.reader(f, delimiter=",")
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# Skip header
next(csv_reader)
for row in csv_reader:
filter_set.add(row[1])
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status("Parsing certificates from %s" % crts_path)
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crt_str = []
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with open(crts_path, "r", encoding="utf-8") as f:
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crt_str = f.read()
# Split all certs into a list of (name, certificate string) tuples
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pem_crts = re.findall(
r"(^.+?)\n(=+\n[\s\S]+?END CERTIFICATE-----\n)", crt_str, re.MULTILINE
)
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filtered_crts = ""
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for name, crt in pem_crts:
if name in filter_set:
filtered_crts += crt
self.add_from_pem(filtered_crts)
class InputError(RuntimeError):
def __init__(self, e):
super(InputError, self).__init__(e)
def main():
global quiet
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parser = argparse.ArgumentParser(description="ESP-IDF x509 certificate bundle utility")
parser.add_argument(
"--quiet",
"-q",
help="Don't print non-critical status messages to stderr",
action="store_true",
)
parser.add_argument(
"--input",
"-i",
nargs="+",
required=True,
help="Paths to the custom certificate folders or files to parse, parses all .pem or .der files",
)
parser.add_argument(
"--filter",
"-f",
help="Path to CSV-file where the second columns contains the name of the certificates \
that should be included from cacrt_all.pem",
)
parser.add_argument(
"--asm",
"-S",
action="store_true",
default=False,
help="Output an asm file for use with gas, rather than a binary file",
)
parser.add_argument("--symbol", help="The symbol to define", default="x509_crt_bundle")
parser.add_argument("--output", "-o", help="The output file", default=None)
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args = parser.parse_args()
quiet = args.quiet
bundle = CertificateBundle()
for path in args.input:
if os.path.isfile(path):
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if os.path.basename(path) == "cacrt_all.pem" and args.filter:
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bundle.add_with_filter(path, args.filter)
else:
bundle.add_from_file(path)
elif os.path.isdir(path):
bundle.add_from_path(path)
else:
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raise InputError("Invalid --input=%s, is neither file nor folder" % args.input)
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status("Successfully added %d certificates in total" % len(bundle.certificates))
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crt_bundle = bundle.create_bundle()
if args.asm:
symbol = args.symbol
filename = args.output or (ca_bundle_bin_file + ".S")
with open(filename, "w") as f:
print(
textwrap.dedent(
f"""\
// Generated from {" ".join(args.input)} with {len(bundle.certificates)} certificates
.data
.section .rodata.embedded
.global {symbol}
.global _binary_{symbol}_start
.global _binary_{symbol}_end
{symbol}:
_binary_{symbol}_start:
"""
),
file=f,
)
for i in range(0, len(crt_bundle), 16):
chunk = crt_bundle[i : i + 16]
formatted = ", ".join(f"0x{byte:02x}" for byte in chunk)
print(f".byte {formatted}", file=f)
print(
textwrap.dedent(
f"""\
_binary_{symbol}_end:
{symbol}_length:
.word {len(crt_bundle)}
"""
),
file=f,
)
else:
filename = args.output or ca_bundle_bin_file
with open(filename, "wb") as f:
f.write(crt_bundle)
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if __name__ == "__main__":
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try:
main()
except InputError as e:
print(e)
sys.exit(2)