move openssl asn1 decode functions to a new module

1 files changed, 717 insertions, 0 deletions

diff --git a/src/cryptography/hazmat/backends/openssl/decode_asn1.py b/src/cryptography/hazmat/backends/openssl/decode_asn1.py
new file mode 100644
index 00000000..c0cc01a8
--- /dev/null
+++ b/src/cryptography/hazmat/backends/openssl/decode_asn1.py
@@ -0,0 +1,717 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
+from __future__ import absolute_import, division, print_function
+
+import ipaddress
+
+from email.utils import parseaddr
+
+import idna
+
+import six
+
+from six.moves import urllib_parse
+
+from cryptography import x509
+from cryptography.x509.oid import (
+    CRLEntryExtensionOID, CertificatePoliciesOID, ExtensionOID
+)
+
+
+def _obj2txt(backend, obj):
+    # Set to 80 on the recommendation of
+    # https://www.openssl.org/docs/crypto/OBJ_nid2ln.html#return_values
+    buf_len = 80
+    buf = backend._ffi.new("char[]", buf_len)
+    res = backend._lib.OBJ_obj2txt(buf, buf_len, obj, 1)
+    backend.openssl_assert(res > 0)
+    return backend._ffi.buffer(buf, res)[:].decode()
+
+
+def _decode_x509_name_entry(backend, x509_name_entry):
+    obj = backend._lib.X509_NAME_ENTRY_get_object(x509_name_entry)
+    backend.openssl_assert(obj != backend._ffi.NULL)
+    data = backend._lib.X509_NAME_ENTRY_get_data(x509_name_entry)
+    backend.openssl_assert(data != backend._ffi.NULL)
+    value = backend._asn1_string_to_utf8(data)
+    oid = _obj2txt(backend, obj)
+
+    return x509.NameAttribute(x509.ObjectIdentifier(oid), value)
+
+
+def _decode_x509_name(backend, x509_name):
+    count = backend._lib.X509_NAME_entry_count(x509_name)
+    attributes = []
+    for x in range(count):
+        entry = backend._lib.X509_NAME_get_entry(x509_name, x)
+        attributes.append(_decode_x509_name_entry(backend, entry))
+
+    return x509.Name(attributes)
+
+
+def _decode_general_names(backend, gns):
+    num = backend._lib.sk_GENERAL_NAME_num(gns)
+    names = []
+    for i in range(num):
+        gn = backend._lib.sk_GENERAL_NAME_value(gns, i)
+        backend.openssl_assert(gn != backend._ffi.NULL)
+        names.append(_decode_general_name(backend, gn))
+
+    return names
+
+
+def _decode_general_name(backend, gn):
+    if gn.type == backend._lib.GEN_DNS:
+        data = backend._asn1_string_to_bytes(gn.d.dNSName)
+        if not data:
+            decoded = u""
+        elif data.startswith(b"*."):
+            # This is a wildcard name. We need to remove the leading wildcard,
+            # IDNA decode, then re-add the wildcard. Wildcard characters should
+            # always be left-most (RFC 2595 section 2.4).
+            decoded = u"*." + idna.decode(data[2:])
+        else:
+            # Not a wildcard, decode away. If the string has a * in it anywhere
+            # invalid this will raise an InvalidCodePoint
+            decoded = idna.decode(data)
+            if data.startswith(b"."):
+                # idna strips leading periods. Name constraints can have that
+                # so we need to re-add it. Sigh.
+                decoded = u"." + decoded
+
+        return x509.DNSName(decoded)
+    elif gn.type == backend._lib.GEN_URI:
+        data = backend._asn1_string_to_ascii(gn.d.uniformResourceIdentifier)
+        parsed = urllib_parse.urlparse(data)
+        if parsed.hostname:
+            hostname = idna.decode(parsed.hostname)
+        else:
+            hostname = ""
+        if parsed.port:
+            netloc = hostname + u":" + six.text_type(parsed.port)
+        else:
+            netloc = hostname
+
+        # Note that building a URL in this fashion means it should be
+        # semantically indistinguishable from the original but is not
+        # guaranteed to be exactly the same.
+        uri = urllib_parse.urlunparse((
+            parsed.scheme,
+            netloc,
+            parsed.path,
+            parsed.params,
+            parsed.query,
+            parsed.fragment
+        ))
+        return x509.UniformResourceIdentifier(uri)
+    elif gn.type == backend._lib.GEN_RID:
+        oid = _obj2txt(backend, gn.d.registeredID)
+        return x509.RegisteredID(x509.ObjectIdentifier(oid))
+    elif gn.type == backend._lib.GEN_IPADD:
+        data = backend._asn1_string_to_bytes(gn.d.iPAddress)
+        data_len = len(data)
+        if data_len == 8 or data_len == 32:
+            # This is an IPv4 or IPv6 Network and not a single IP. This
+            # type of data appears in Name Constraints. Unfortunately,
+            # ipaddress doesn't support packed bytes + netmask. Additionally,
+            # IPv6Network can only handle CIDR rather than the full 16 byte
+            # netmask. To handle this we convert the netmask to integer, then
+            # find the first 0 bit, which will be the prefix. If another 1
+            # bit is present after that the netmask is invalid.
+            base = ipaddress.ip_address(data[:data_len // 2])
+            netmask = ipaddress.ip_address(data[data_len // 2:])
+            bits = bin(int(netmask))[2:]
+            prefix = bits.find('0')
+            # If no 0 bits are found it is a /32 or /128
+            if prefix == -1:
+                prefix = len(bits)
+
+            if "1" in bits[prefix:]:
+                raise ValueError("Invalid netmask")
+
+            ip = ipaddress.ip_network(base.exploded + u"/{0}".format(prefix))
+        else:
+            ip = ipaddress.ip_address(data)
+
+        return x509.IPAddress(ip)
+    elif gn.type == backend._lib.GEN_DIRNAME:
+        return x509.DirectoryName(
+            _decode_x509_name(backend, gn.d.directoryName)
+        )
+    elif gn.type == backend._lib.GEN_EMAIL:
+        data = backend._asn1_string_to_ascii(gn.d.rfc822Name)
+        name, address = parseaddr(data)
+        parts = address.split(u"@")
+        if name or not address:
+            # parseaddr has found a name (e.g. Name <email>) or the entire
+            # value is an empty string.
+            raise ValueError("Invalid rfc822name value")
+        elif len(parts) == 1:
+            # Single label email name. This is valid for local delivery. No
+            # IDNA decoding can be done since there is no domain component.
+            return x509.RFC822Name(address)
+        else:
+            # A normal email of the form user@domain.com. Let's attempt to
+            # decode the domain component and return the entire address.
+            return x509.RFC822Name(
+                parts[0] + u"@" + idna.decode(parts[1])
+            )
+    elif gn.type == backend._lib.GEN_OTHERNAME:
+        type_id = _obj2txt(backend, gn.d.otherName.type_id)
+        value = backend._asn1_to_der(gn.d.otherName.value)
+        return x509.OtherName(x509.ObjectIdentifier(type_id), value)
+    else:
+        # x400Address or ediPartyName
+        raise x509.UnsupportedGeneralNameType(
+            "{0} is not a supported type".format(
+                x509._GENERAL_NAMES.get(gn.type, gn.type)
+            ),
+            gn.type
+        )
+
+
+def _decode_ocsp_no_check(backend, ext):
+    return x509.OCSPNoCheck()
+
+
+def _decode_crl_number(backend, ext):
+    asn1_int = backend._ffi.cast("ASN1_INTEGER *", ext)
+    asn1_int = backend._ffi.gc(asn1_int, backend._lib.ASN1_INTEGER_free)
+    return x509.CRLNumber(backend._asn1_integer_to_int(asn1_int))
+
+
+class _X509ExtensionParser(object):
+    def __init__(self, ext_count, get_ext, handlers, unsupported_exts=None):
+        self.ext_count = ext_count
+        self.get_ext = get_ext
+        self.handlers = handlers
+        self.unsupported_exts = unsupported_exts
+
+    def parse(self, backend, x509_obj):
+        extensions = []
+        seen_oids = set()
+        for i in range(self.ext_count(backend, x509_obj)):
+            ext = self.get_ext(backend, x509_obj, i)
+            backend.openssl_assert(ext != backend._ffi.NULL)
+            crit = backend._lib.X509_EXTENSION_get_critical(ext)
+            critical = crit == 1
+            oid = x509.ObjectIdentifier(_obj2txt(backend, ext.object))
+            if oid in seen_oids:
+                raise x509.DuplicateExtension(
+                    "Duplicate {0} extension found".format(oid), oid
+                )
+            try:
+                handler = self.handlers[oid]
+            except KeyError:
+                if critical:
+                    raise x509.UnsupportedExtension(
+                        "Critical extension {0} is not currently supported"
+                        .format(oid), oid
+                    )
+                else:
+                    # Dump the DER payload into an UnrecognizedExtension object
+                    data = backend._lib.X509_EXTENSION_get_data(ext)
+                    backend.openssl_assert(data != backend._ffi.NULL)
+                    der = backend._ffi.buffer(data.data, data.length)[:]
+                    unrecognized = x509.UnrecognizedExtension(oid, der)
+                    extensions.append(
+                        x509.Extension(oid, critical, unrecognized)
+                    )
+            else:
+                # For extensions which are not supported by OpenSSL we pass the
+                # extension object directly to the parsing routine so it can
+                # be decoded manually.
+                if self.unsupported_exts and oid in self.unsupported_exts:
+                    ext_data = ext
+                else:
+                    ext_data = backend._lib.X509V3_EXT_d2i(ext)
+                    if ext_data == backend._ffi.NULL:
+                        backend._consume_errors()
+                        raise ValueError(
+                            "The {0} extension is invalid and can't be "
+                            "parsed".format(oid)
+                        )
+
+                value = handler(backend, ext_data)
+                extensions.append(x509.Extension(oid, critical, value))
+
+            seen_oids.add(oid)
+
+        return x509.Extensions(extensions)
+
+
+def _decode_certificate_policies(backend, cp):
+    cp = backend._ffi.cast("Cryptography_STACK_OF_POLICYINFO *", cp)
+    cp = backend._ffi.gc(cp, backend._lib.sk_POLICYINFO_free)
+    num = backend._lib.sk_POLICYINFO_num(cp)
+    certificate_policies = []
+    for i in range(num):
+        qualifiers = None
+        pi = backend._lib.sk_POLICYINFO_value(cp, i)
+        oid = x509.ObjectIdentifier(_obj2txt(backend, pi.policyid))
+        if pi.qualifiers != backend._ffi.NULL:
+            qnum = backend._lib.sk_POLICYQUALINFO_num(pi.qualifiers)
+            qualifiers = []
+            for j in range(qnum):
+                pqi = backend._lib.sk_POLICYQUALINFO_value(
+                    pi.qualifiers, j
+                )
+                pqualid = x509.ObjectIdentifier(
+                    _obj2txt(backend, pqi.pqualid)
+                )
+                if pqualid == CertificatePoliciesOID.CPS_QUALIFIER:
+                    cpsuri = backend._ffi.buffer(
+                        pqi.d.cpsuri.data, pqi.d.cpsuri.length
+                    )[:].decode('ascii')
+                    qualifiers.append(cpsuri)
+                else:
+                    assert pqualid == CertificatePoliciesOID.CPS_USER_NOTICE
+                    user_notice = _decode_user_notice(
+                        backend, pqi.d.usernotice
+                    )
+                    qualifiers.append(user_notice)
+
+        certificate_policies.append(
+            x509.PolicyInformation(oid, qualifiers)
+        )
+
+    return x509.CertificatePolicies(certificate_policies)
+
+
+def _decode_user_notice(backend, un):
+    explicit_text = None
+    notice_reference = None
+
+    if un.exptext != backend._ffi.NULL:
+        explicit_text = backend._asn1_string_to_utf8(un.exptext)
+
+    if un.noticeref != backend._ffi.NULL:
+        organization = backend._asn1_string_to_utf8(un.noticeref.organization)
+
+        num = backend._lib.sk_ASN1_INTEGER_num(
+            un.noticeref.noticenos
+        )
+        notice_numbers = []
+        for i in range(num):
+            asn1_int = backend._lib.sk_ASN1_INTEGER_value(
+                un.noticeref.noticenos, i
+            )
+            notice_num = backend._asn1_integer_to_int(asn1_int)
+            notice_numbers.append(notice_num)
+
+        notice_reference = x509.NoticeReference(
+            organization, notice_numbers
+        )
+
+    return x509.UserNotice(notice_reference, explicit_text)
+
+
+def _decode_basic_constraints(backend, bc_st):
+    basic_constraints = backend._ffi.cast("BASIC_CONSTRAINTS *", bc_st)
+    basic_constraints = backend._ffi.gc(
+        basic_constraints, backend._lib.BASIC_CONSTRAINTS_free
+    )
+    # The byte representation of an ASN.1 boolean true is \xff. OpenSSL
+    # chooses to just map this to its ordinal value, so true is 255 and
+    # false is 0.
+    ca = basic_constraints.ca == 255
+    if basic_constraints.pathlen == backend._ffi.NULL:
+        path_length = None
+    else:
+        path_length = backend._asn1_integer_to_int(basic_constraints.pathlen)
+
+    return x509.BasicConstraints(ca, path_length)
+
+
+def _decode_subject_key_identifier(backend, asn1_string):
+    asn1_string = backend._ffi.cast("ASN1_OCTET_STRING *", asn1_string)
+    asn1_string = backend._ffi.gc(
+        asn1_string, backend._lib.ASN1_OCTET_STRING_free
+    )
+    return x509.SubjectKeyIdentifier(
+        backend._ffi.buffer(asn1_string.data, asn1_string.length)[:]
+    )
+
+
+def _decode_authority_key_identifier(backend, akid):
+    akid = backend._ffi.cast("AUTHORITY_KEYID *", akid)
+    akid = backend._ffi.gc(akid, backend._lib.AUTHORITY_KEYID_free)
+    key_identifier = None
+    authority_cert_issuer = None
+    authority_cert_serial_number = None
+
+    if akid.keyid != backend._ffi.NULL:
+        key_identifier = backend._ffi.buffer(
+            akid.keyid.data, akid.keyid.length
+        )[:]
+
+    if akid.issuer != backend._ffi.NULL:
+        authority_cert_issuer = _decode_general_names(
+            backend, akid.issuer
+        )
+
+    if akid.serial != backend._ffi.NULL:
+        authority_cert_serial_number = backend._asn1_integer_to_int(
+            akid.serial
+        )
+
+    return x509.AuthorityKeyIdentifier(
+        key_identifier, authority_cert_issuer, authority_cert_serial_number
+    )
+
+
+def _decode_authority_information_access(backend, aia):
+    aia = backend._ffi.cast("Cryptography_STACK_OF_ACCESS_DESCRIPTION *", aia)
+    aia = backend._ffi.gc(aia, backend._lib.sk_ACCESS_DESCRIPTION_free)
+    num = backend._lib.sk_ACCESS_DESCRIPTION_num(aia)
+    access_descriptions = []
+    for i in range(num):
+        ad = backend._lib.sk_ACCESS_DESCRIPTION_value(aia, i)
+        backend.openssl_assert(ad.method != backend._ffi.NULL)
+        oid = x509.ObjectIdentifier(_obj2txt(backend, ad.method))
+        backend.openssl_assert(ad.location != backend._ffi.NULL)
+        gn = _decode_general_name(backend, ad.location)
+        access_descriptions.append(x509.AccessDescription(oid, gn))
+
+    return x509.AuthorityInformationAccess(access_descriptions)
+
+
+def _decode_key_usage(backend, bit_string):
+    bit_string = backend._ffi.cast("ASN1_BIT_STRING *", bit_string)
+    bit_string = backend._ffi.gc(bit_string, backend._lib.ASN1_BIT_STRING_free)
+    get_bit = backend._lib.ASN1_BIT_STRING_get_bit
+    digital_signature = get_bit(bit_string, 0) == 1
+    content_commitment = get_bit(bit_string, 1) == 1
+    key_encipherment = get_bit(bit_string, 2) == 1
+    data_encipherment = get_bit(bit_string, 3) == 1
+    key_agreement = get_bit(bit_string, 4) == 1
+    key_cert_sign = get_bit(bit_string, 5) == 1
+    crl_sign = get_bit(bit_string, 6) == 1
+    encipher_only = get_bit(bit_string, 7) == 1
+    decipher_only = get_bit(bit_string, 8) == 1
+    return x509.KeyUsage(
+        digital_signature,
+        content_commitment,
+        key_encipherment,
+        data_encipherment,
+        key_agreement,
+        key_cert_sign,
+        crl_sign,
+        encipher_only,
+        decipher_only
+    )
+
+
+def _decode_general_names_extension(backend, gns):
+    gns = backend._ffi.cast("GENERAL_NAMES *", gns)
+    gns = backend._ffi.gc(gns, backend._lib.GENERAL_NAMES_free)
+    general_names = _decode_general_names(backend, gns)
+    return general_names
+
+
+def _decode_subject_alt_name(backend, ext):
+    return x509.SubjectAlternativeName(
+        _decode_general_names_extension(backend, ext)
+    )
+
+
+def _decode_issuer_alt_name(backend, ext):
+    return x509.IssuerAlternativeName(
+        _decode_general_names_extension(backend, ext)
+    )
+
+
+def _decode_name_constraints(backend, nc):
+    nc = backend._ffi.cast("NAME_CONSTRAINTS *", nc)
+    nc = backend._ffi.gc(nc, backend._lib.NAME_CONSTRAINTS_free)
+    permitted = _decode_general_subtrees(backend, nc.permittedSubtrees)
+    excluded = _decode_general_subtrees(backend, nc.excludedSubtrees)
+    return x509.NameConstraints(
+        permitted_subtrees=permitted, excluded_subtrees=excluded
+    )
+
+
+def _decode_general_subtrees(backend, stack_subtrees):
+    if stack_subtrees == backend._ffi.NULL:
+        return None
+
+    num = backend._lib.sk_GENERAL_SUBTREE_num(stack_subtrees)
+    subtrees = []
+
+    for i in range(num):
+        obj = backend._lib.sk_GENERAL_SUBTREE_value(stack_subtrees, i)
+        backend.openssl_assert(obj != backend._ffi.NULL)
+        name = _decode_general_name(backend, obj.base)
+        subtrees.append(name)
+
+    return subtrees
+
+
+def _decode_extended_key_usage(backend, sk):
+    sk = backend._ffi.cast("Cryptography_STACK_OF_ASN1_OBJECT *", sk)
+    sk = backend._ffi.gc(sk, backend._lib.sk_ASN1_OBJECT_free)
+    num = backend._lib.sk_ASN1_OBJECT_num(sk)
+    ekus = []
+
+    for i in range(num):
+        obj = backend._lib.sk_ASN1_OBJECT_value(sk, i)
+        backend.openssl_assert(obj != backend._ffi.NULL)
+        oid = x509.ObjectIdentifier(_obj2txt(backend, obj))
+        ekus.append(oid)
+
+    return x509.ExtendedKeyUsage(ekus)
+
+
+_DISTPOINT_TYPE_FULLNAME = 0
+_DISTPOINT_TYPE_RELATIVENAME = 1
+
+
+def _decode_crl_distribution_points(backend, cdps):
+    cdps = backend._ffi.cast("Cryptography_STACK_OF_DIST_POINT *", cdps)
+    cdps = backend._ffi.gc(cdps, backend._lib.sk_DIST_POINT_free)
+    num = backend._lib.sk_DIST_POINT_num(cdps)
+
+    dist_points = []
+    for i in range(num):
+        full_name = None
+        relative_name = None
+        crl_issuer = None
+        reasons = None
+        cdp = backend._lib.sk_DIST_POINT_value(cdps, i)
+        if cdp.reasons != backend._ffi.NULL:
+            # We will check each bit from RFC 5280
+            # ReasonFlags ::= BIT STRING {
+            #      unused                  (0),
+            #      keyCompromise           (1),
+            #      cACompromise            (2),
+            #      affiliationChanged      (3),
+            #      superseded              (4),
+            #      cessationOfOperation    (5),
+            #      certificateHold         (6),
+            #      privilegeWithdrawn      (7),
+            #      aACompromise            (8) }
+            reasons = []
+            get_bit = backend._lib.ASN1_BIT_STRING_get_bit
+            if get_bit(cdp.reasons, 1):
+                reasons.append(x509.ReasonFlags.key_compromise)
+
+            if get_bit(cdp.reasons, 2):
+                reasons.append(x509.ReasonFlags.ca_compromise)
+
+            if get_bit(cdp.reasons, 3):
+                reasons.append(x509.ReasonFlags.affiliation_changed)
+
+            if get_bit(cdp.reasons, 4):
+                reasons.append(x509.ReasonFlags.superseded)
+
+            if get_bit(cdp.reasons, 5):
+                reasons.append(x509.ReasonFlags.cessation_of_operation)
+
+            if get_bit(cdp.reasons, 6):
+                reasons.append(x509.ReasonFlags.certificate_hold)
+
+            if get_bit(cdp.reasons, 7):
+                reasons.append(x509.ReasonFlags.privilege_withdrawn)
+
+            if get_bit(cdp.reasons, 8):
+                reasons.append(x509.ReasonFlags.aa_compromise)
+
+            reasons = frozenset(reasons)
+
+        if cdp.CRLissuer != backend._ffi.NULL:
+            crl_issuer = _decode_general_names(backend, cdp.CRLissuer)
+
+        # Certificates may have a crl_issuer/reasons and no distribution
+        # point so make sure it's not null.
+        if cdp.distpoint != backend._ffi.NULL:
+            # Type 0 is fullName, there is no #define for it in the code.
+            if cdp.distpoint.type == _DISTPOINT_TYPE_FULLNAME:
+                full_name = _decode_general_names(
+                    backend, cdp.distpoint.name.fullname
+                )
+            # OpenSSL code doesn't test for a specific type for
+            # relativename, everything that isn't fullname is considered
+            # relativename.
+            else:
+                rns = cdp.distpoint.name.relativename
+                rnum = backend._lib.sk_X509_NAME_ENTRY_num(rns)
+                attributes = []
+                for i in range(rnum):
+                    rn = backend._lib.sk_X509_NAME_ENTRY_value(
+                        rns, i
+                    )
+                    backend.openssl_assert(rn != backend._ffi.NULL)
+                    attributes.append(
+                        _decode_x509_name_entry(backend, rn)
+                    )
+
+                relative_name = x509.Name(attributes)
+
+        dist_points.append(
+            x509.DistributionPoint(
+                full_name, relative_name, reasons, crl_issuer
+            )
+        )
+
+    return x509.CRLDistributionPoints(dist_points)
+
+
+def _decode_inhibit_any_policy(backend, asn1_int):
+    asn1_int = backend._ffi.cast("ASN1_INTEGER *", asn1_int)
+    asn1_int = backend._ffi.gc(asn1_int, backend._lib.ASN1_INTEGER_free)
+    skip_certs = backend._asn1_integer_to_int(asn1_int)
+    return x509.InhibitAnyPolicy(skip_certs)
+
+
+#    CRLReason ::= ENUMERATED {
+#        unspecified             (0),
+#        keyCompromise           (1),
+#        cACompromise            (2),
+#        affiliationChanged      (3),
+#        superseded              (4),
+#        cessationOfOperation    (5),
+#        certificateHold         (6),
+#             -- value 7 is not used
+#        removeFromCRL           (8),
+#        privilegeWithdrawn      (9),
+#        aACompromise           (10) }
+_CRL_ENTRY_REASON_CODE_TO_ENUM = {
+    0: x509.ReasonFlags.unspecified,
+    1: x509.ReasonFlags.key_compromise,
+    2: x509.ReasonFlags.ca_compromise,
+    3: x509.ReasonFlags.affiliation_changed,
+    4: x509.ReasonFlags.superseded,
+    5: x509.ReasonFlags.cessation_of_operation,
+    6: x509.ReasonFlags.certificate_hold,
+    8: x509.ReasonFlags.remove_from_crl,
+    9: x509.ReasonFlags.privilege_withdrawn,
+    10: x509.ReasonFlags.aa_compromise,
+}
+
+
+_CRL_ENTRY_REASON_ENUM_TO_CODE = {
+    x509.ReasonFlags.unspecified: 0,
+    x509.ReasonFlags.key_compromise: 1,
+    x509.ReasonFlags.ca_compromise: 2,
+    x509.ReasonFlags.affiliation_changed: 3,
+    x509.ReasonFlags.superseded: 4,
+    x509.ReasonFlags.cessation_of_operation: 5,
+    x509.ReasonFlags.certificate_hold: 6,
+    x509.ReasonFlags.remove_from_crl: 8,
+    x509.ReasonFlags.privilege_withdrawn: 9,
+    x509.ReasonFlags.aa_compromise: 10
+}
+
+
+def _decode_crl_reason(backend, enum):
+    enum = backend._ffi.cast("ASN1_ENUMERATED *", enum)
+    enum = backend._ffi.gc(enum, backend._lib.ASN1_ENUMERATED_free)
+    code = backend._lib.ASN1_ENUMERATED_get(enum)
+
+    try:
+        return x509.CRLReason(_CRL_ENTRY_REASON_CODE_TO_ENUM[code])
+    except KeyError:
+        raise ValueError("Unsupported reason code: {0}".format(code))
+
+
+def _decode_invalidity_date(backend, inv_date):
+    generalized_time = backend._ffi.cast(
+        "ASN1_GENERALIZEDTIME *", inv_date
+    )
+    generalized_time = backend._ffi.gc(
+        generalized_time, backend._lib.ASN1_GENERALIZEDTIME_free
+    )
+    return x509.InvalidityDate(
+        backend._parse_asn1_generalized_time(generalized_time)
+    )
+
+
+def _decode_cert_issuer(backend, ext):
+    """
+    This handler decodes the CertificateIssuer entry extension directly
+    from the X509_EXTENSION object. This is necessary because this entry
+    extension is not directly supported by OpenSSL 0.9.8.
+    """
+
+    data_ptr_ptr = backend._ffi.new("const unsigned char **")
+    data_ptr_ptr[0] = ext.value.data
+    gns = backend._lib.d2i_GENERAL_NAMES(
+        backend._ffi.NULL, data_ptr_ptr, ext.value.length
+    )
+
+    # Check the result of d2i_GENERAL_NAMES() is valid. Usually this is covered
+    # in _X509ExtensionParser but since we are responsible for decoding this
+    # entry extension ourselves, we have to this here.
+    if gns == backend._ffi.NULL:
+        backend._consume_errors()
+        raise ValueError(
+            "The {0} extension is corrupted and can't be parsed".format(
+                CRLEntryExtensionOID.CERTIFICATE_ISSUER))
+
+    gns = backend._ffi.gc(gns, backend._lib.GENERAL_NAMES_free)
+    return x509.CertificateIssuer(_decode_general_names(backend, gns))
+
+
+_EXTENSION_HANDLERS = {
+    ExtensionOID.BASIC_CONSTRAINTS: _decode_basic_constraints,
+    ExtensionOID.SUBJECT_KEY_IDENTIFIER: _decode_subject_key_identifier,
+    ExtensionOID.KEY_USAGE: _decode_key_usage,
+    ExtensionOID.SUBJECT_ALTERNATIVE_NAME: _decode_subject_alt_name,
+    ExtensionOID.EXTENDED_KEY_USAGE: _decode_extended_key_usage,
+    ExtensionOID.AUTHORITY_KEY_IDENTIFIER: _decode_authority_key_identifier,
+    ExtensionOID.AUTHORITY_INFORMATION_ACCESS: (
+        _decode_authority_information_access
+    ),
+    ExtensionOID.CERTIFICATE_POLICIES: _decode_certificate_policies,
+    ExtensionOID.CRL_DISTRIBUTION_POINTS: _decode_crl_distribution_points,
+    ExtensionOID.OCSP_NO_CHECK: _decode_ocsp_no_check,
+    ExtensionOID.INHIBIT_ANY_POLICY: _decode_inhibit_any_policy,
+    ExtensionOID.ISSUER_ALTERNATIVE_NAME: _decode_issuer_alt_name,
+    ExtensionOID.NAME_CONSTRAINTS: _decode_name_constraints,
+}
+
+_REVOKED_EXTENSION_HANDLERS = {
+    CRLEntryExtensionOID.CRL_REASON: _decode_crl_reason,
+    CRLEntryExtensionOID.INVALIDITY_DATE: _decode_invalidity_date,
+    CRLEntryExtensionOID.CERTIFICATE_ISSUER: _decode_cert_issuer,
+}
+
+_REVOKED_UNSUPPORTED_EXTENSIONS = set([
+    CRLEntryExtensionOID.CERTIFICATE_ISSUER,
+])
+
+_CRL_EXTENSION_HANDLERS = {
+    ExtensionOID.CRL_NUMBER: _decode_crl_number,
+    ExtensionOID.AUTHORITY_KEY_IDENTIFIER: _decode_authority_key_identifier,
+    ExtensionOID.ISSUER_ALTERNATIVE_NAME: _decode_issuer_alt_name,
+    ExtensionOID.AUTHORITY_INFORMATION_ACCESS: (
+        _decode_authority_information_access
+    ),
+}
+
+_CERTIFICATE_EXTENSION_PARSER = _X509ExtensionParser(
+    ext_count=lambda backend, x: backend._lib.X509_get_ext_count(x),
+    get_ext=lambda backend, x, i: backend._lib.X509_get_ext(x, i),
+    handlers=_EXTENSION_HANDLERS
+)
+
+_CSR_EXTENSION_PARSER = _X509ExtensionParser(
+    ext_count=lambda backend, x: backend._lib.sk_X509_EXTENSION_num(x),
+    get_ext=lambda backend, x, i: backend._lib.sk_X509_EXTENSION_value(x, i),
+    handlers=_EXTENSION_HANDLERS
+)
+
+_REVOKED_CERTIFICATE_EXTENSION_PARSER = _X509ExtensionParser(
+    ext_count=lambda backend, x: backend._lib.X509_REVOKED_get_ext_count(x),
+    get_ext=lambda backend, x, i: backend._lib.X509_REVOKED_get_ext(x, i),
+    handlers=_REVOKED_EXTENSION_HANDLERS,
+    unsupported_exts=_REVOKED_UNSUPPORTED_EXTENSIONS
+)
+
+_CRL_EXTENSION_PARSER = _X509ExtensionParser(
+    ext_count=lambda backend, x: backend._lib.X509_CRL_get_ext_count(x),
+    get_ext=lambda backend, x, i: backend._lib.X509_CRL_get_ext(x, i),
+    handlers=_CRL_EXTENSION_HANDLERS,
+)