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# coding: utf-8
from __future__ import unicode_literals, division, absolute_import, print_function
import os
import sys
from asn1crypto import core, ocsp, x509, algos, util
from . import errors
from ._types import str_cls, type_name
from ._version import __version__
if sys.version_info < (3,):
from urllib2 import Request, urlopen, URLError
else:
from urllib.request import Request, urlopen
from urllib.error import URLError
def fetch(cert, issuer, hash_algo='sha1', nonce=True, user_agent=None, timeout=10):
"""
Fetches an OCSP response for a certificate
:param cert:
An asn1cyrpto.x509.Certificate object to get an OCSP reponse for
:param issuer:
An asn1crypto.x509.Certificate object that is the issuer of cert
:param hash_algo:
A unicode string of "sha1" or "sha256"
:param nonce:
A boolean - if the nonce extension should be used to prevent replay
attacks
:param user_agent:
The HTTP user agent to use when requesting the OCSP response. If None,
a default is used in the format "certvalidation 1.0.0".
:param timeout:
The number of seconds after which an HTTP request should timeout
:raises:
urllib.error.URLError/urllib2.URLError - when a URL/HTTP error occurs
socket.error - when a socket error occurs
:return:
An asn1crypto.ocsp.OCSPResponse object
"""
if not isinstance(cert, x509.Certificate):
raise TypeError('cert must be an instance of asn1crypto.x509.Certificate, not %s' % type_name(cert))
if not isinstance(issuer, x509.Certificate):
raise TypeError('issuer must be an instance of asn1crypto.x509.Certificate, not %s' % type_name(issuer))
if hash_algo not in set(['sha1', 'sha256']):
raise ValueError('hash_algo must be one of "sha1", "sha256", not %s' % repr(hash_algo))
if not isinstance(nonce, bool):
raise TypeError('nonce must be a bool, not %s' % type_name(nonce))
if user_agent is None:
user_agent = 'certvalidator %s' % __version__
elif not isinstance(user_agent, str_cls):
raise TypeError('user_agent must be a unicode string, not %s' % type_name(user_agent))
cert_id = ocsp.CertId({
'hash_algorithm': algos.DigestAlgorithm({'algorithm': hash_algo}),
'issuer_name_hash': getattr(cert.issuer, hash_algo),
'issuer_key_hash': getattr(issuer.public_key, hash_algo),
'serial_number': cert.serial_number,
})
request = ocsp.Request({
'req_cert': cert_id,
})
tbs_request = ocsp.TBSRequest({
'request_list': ocsp.Requests([request]),
})
if nonce:
nonce_extension = ocsp.TBSRequestExtension({
'extn_id': 'nonce',
'critical': False,
'extn_value': core.OctetString(core.OctetString(os.urandom(16)).dump())
})
tbs_request['request_extensions'] = ocsp.TBSRequestExtensions([nonce_extension])
ocsp_request = ocsp.OCSPRequest({
'tbs_request': tbs_request,
})
last_e = None
for ocsp_url in cert.ocsp_urls:
try:
if sys.version_info < (3,):
ocsp_url = util.iri_to_uri(ocsp_url)
request = Request(ocsp_url)
_add_header(request, 'Accept', 'application/ocsp-response')
_add_header(request, 'Content-Type', 'application/ocsp-request')
_add_header(request, 'User-Agent', user_agent)
response = urlopen(request, ocsp_request.dump(), timeout)
ocsp_response = ocsp.OCSPResponse.load(response.read())
request_nonce = ocsp_request.nonce_value
response_nonce = ocsp_response.nonce_value
if request_nonce and response_nonce and request_nonce.native != response_nonce.native:
raise errors.OCSPValidationError(
'Unable to verify OCSP response since the request and response nonces do not match'
)
return ocsp_response
except (URLError) as e:
last_e = e
raise last_e
def _add_header(request, name, value):
"""
Adds a header to a urllib2/urllib.request Request object, ensuring values
are encoded appropriately based on the version of Python
:param request:
An instance of urllib2.Request or urllib.request.Request
:param name:
A unicode string of the header name
:param value:
A unicode string of the header value
"""
if sys.version_info < (3,):
name = name.encode('iso-8859-1')
value = value.encode('iso-8859-1')
request.add_header(name, value)
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