fetch-ocsp-response

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

# nghttp2 - HTTP/2 C Library

# Copyright (c) 2015 Tatsuhiro Tsujikawa

# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:

# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

# This program was translated from the program originally developed by
# h2o project (https://github.com/h2o/h2o), written in Perl.  It had
# the following copyright notice:

# Copyright (c) 2015 DeNA Co., Ltd.
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to
# deal in the Software without restriction, including without limitation the
# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
# sell copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
# IN THE SOFTWARE.

from __future__ import unicode_literals
import argparse
import io
import os
import os.path
import re
import shutil
import subprocess
import sys
import tempfile

# make this program work for both Python 3 and Python 2.
try:
    from urllib.parse import urlparse
    stdout_bwrite = sys.stdout.buffer.write
except ImportError:
    from urlparse import urlparse
    stdout_bwrite = sys.stdout.write


def die(msg):
    sys.stderr.write(msg)
    sys.stderr.write('\n')
    sys.exit(255)


def tempfail(msg):
    sys.stderr.write(msg)
    sys.stderr.write('\n')
    sys.exit(os.EX_TEMPFAIL)


def run_openssl(args, allow_tempfail=False):
    buf = io.BytesIO()
    try:
        p = subprocess.Popen(args, stdout=subprocess.PIPE)
    except Exception as e:
        die('failed to invoke {}:{}'.format(args, e))
    try:
        while True:
            data = p.stdout.read()
            if len(data) == 0:
                break
            buf.write(data)
        if p.wait() != 0:
            raise Exception('nonzero return code {}'.format(p.returncode))
        return buf.getvalue()
    except Exception as e:
        msg = 'OpenSSL exited abnormally: {}:{}'.format(args, e)
        tempfail(msg) if allow_tempfail else die(msg)


def read_file(path):
    with open(path, 'rb') as f:
        return f.read()


def write_file(path, data):
    with open(path, 'wb') as f:
        f.write(data)


def detect_openssl_version(cmd):
    return run_openssl([cmd, 'version']).decode('utf-8').strip()


def extract_ocsp_uri(cmd, cert_fn):
    # obtain ocsp uri
    ocsp_uri = run_openssl(
        [cmd, 'x509', '-in', cert_fn, '-noout',
         '-ocsp_uri']).decode('utf-8').strip()

    if not re.match(r'^https?://', ocsp_uri):
        die('failed to extract ocsp URI from {}'.format(cert_fn))

    return ocsp_uri


def save_issuer_certificate(issuer_fn, cert_fn):
    # save issuer certificate
    chain = read_file(cert_fn).decode('utf-8')
    m = re.match(
        r'.*?-----END CERTIFICATE-----.*?(-----BEGIN CERTIFICATE-----.*?-----END CERTIFICATE-----)',
        chain, re.DOTALL)
    if not m:
        die('--issuer option was not used, and failed to extract issuer certificate from the certificate')
    write_file(issuer_fn, (m.group(1) + '\n').encode('utf-8'))


def send_and_receive_ocsp(respder_fn, cmd, cert_fn, issuer_fn, ocsp_uri,
                          ocsp_host, openssl_version):
    # obtain response (without verification)
    sys.stderr.write('sending OCSP request to {}\n'.format(ocsp_uri))
    args = [
        cmd, 'ocsp', '-issuer', issuer_fn, '-cert', cert_fn, '-url', ocsp_uri,
        '-noverify', '-respout', respder_fn
    ]
    ver = openssl_version.lower()
    if ver.startswith('openssl 1.0.') or ver.startswith('libressl '):
        args.extend(['-header', 'Host', ocsp_host])
    resp = run_openssl(args, allow_tempfail=True)
    return resp.decode('utf-8')


def verify_response(cmd, tempdir, issuer_fn, respder_fn):
    # verify the response
    sys.stderr.write('verifying the response signature\n')

    verify_fn = os.path.join(tempdir, 'verify.out')

    # try from exotic options
    allextra = [
        # for comodo
        ['-VAfile', issuer_fn],
        # these options are only available in OpenSSL >= 1.0.2
        ['-partial_chain', '-trusted_first', '-CAfile', issuer_fn],
        # for OpenSSL <= 1.0.1
        ['-CAfile', issuer_fn],
    ]

    for extra in allextra:
        with open(verify_fn, 'w+b') as f:
            args = [cmd, 'ocsp', '-respin', respder_fn]
            args.extend(extra)
            p = subprocess.Popen(args, stdout=f, stderr=f)
            if p.wait() == 0:
                # OpenSSL <= 1.0.1, openssl ocsp still returns exit
                # code 0 even if verification was failed.  So check
                # the error message in stderr output.
                f.seek(0)
                if f.read().decode('utf-8').find(
                        'Response Verify Failure') != -1:
                    continue
                sys.stderr.write('verify OK (used: {})\n'.format(extra))
                return True

    sys.stderr.write(read_file(verify_fn).decode('utf-8'))
    return False


def fetch_ocsp_response(cmd, cert_fn, tempdir, issuer_fn=None):
    openssl_version = detect_openssl_version(cmd)

    sys.stderr.write(
        'fetch-ocsp-response (using {})\n'.format(openssl_version))

    ocsp_uri = extract_ocsp_uri(cmd, cert_fn)
    ocsp_host = urlparse(ocsp_uri).netloc

    if not issuer_fn:
        issuer_fn = os.path.join(tempdir, 'issuer.crt')
        save_issuer_certificate(issuer_fn, cert_fn)

    respder_fn = os.path.join(tempdir, 'resp.der')
    resp = send_and_receive_ocsp(
        respder_fn, cmd, cert_fn, issuer_fn, ocsp_uri, ocsp_host,
        openssl_version)

    sys.stderr.write('{}\n'.format(resp))

    # OpenSSL 1.0.2 still returns exit code 0 even if ocsp responder
    # returned error status (e.g., trylater(3))
    if resp.find('Responder Error:') != -1:
        raise Exception('responder returned error')

    if not verify_response(cmd, tempdir, issuer_fn, respder_fn):
        tempfail('failed to verify the response')

    # success
    res = read_file(respder_fn)
    stdout_bwrite(res)


if __name__ == '__main__':
    parser = argparse.ArgumentParser(
        description=
        '''The command issues an OCSP request for given server certificate, verifies the response and prints the resulting DER.''',
        epilog=
        '''The command exits 0 if successful, or 75 (EX_TEMPFAIL) on temporary error.  Other exit codes may be returned in case of hard errors.''')
    parser.add_argument(
        '--issuer',
        metavar='FILE',
        help=
        'issuer certificate (if omitted, is extracted from the certificate chain)')
    parser.add_argument('--openssl',
                        metavar='CMD',
                        help='openssl command to use (default: "openssl")',
                        default='openssl')
    parser.add_argument('certificate',
                        help='path to certificate file to validate')
    args = parser.parse_args()

    tempdir = None
    try:
        # Python3.2 has tempfile.TemporaryDirectory, which has nice
        # feature to delete its tree by cleanup() function.  We have
        # to support Python2.7, so we have to do this manually.
        tempdir = tempfile.mkdtemp()
        fetch_ocsp_response(args.openssl, args.certificate, tempdir,
                            args.issuer)
    finally:
        if tempdir:
            shutil.rmtree(tempdir)