path: root/src/cryptography/hazmat/backends/openssl/x509.py

# 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 datetime
import ipaddress
from email.utils import parseaddr

import idna

import six

from six.moves import urllib_parse

from cryptography import utils, x509
from cryptography.exceptions import UnsupportedAlgorithm
from cryptography.hazmat.primitives import hashes, serialization


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)
    assert res > 0
    return backend._ffi.buffer(buf, res)[:].decode()


def _asn1_integer_to_int(backend, asn1_int):
    bn = backend._lib.ASN1_INTEGER_to_BN(asn1_int, backend._ffi.NULL)
    assert bn != backend._ffi.NULL
    bn = backend._ffi.gc(bn, backend._lib.BN_free)
    return backend._bn_to_int(bn)


def _asn1_string_to_utf8(backend, asn1_string):
    buf = backend._ffi.new("unsigned char **")
    res = backend._lib.ASN1_STRING_to_UTF8(buf, asn1_string)
    assert res >= 0
    assert buf[0] != backend._ffi.NULL
    buf = backend._ffi.gc(
        buf, lambda buffer: backend._lib.OPENSSL_free(buffer[0])
    )
    return backend._ffi.buffer(buf[0], res)[:].decode('utf8')


def _decode_x509_name_entry(backend, x509_name_entry):
    obj = backend._lib.X509_NAME_ENTRY_get_object(x509_name_entry)
    assert obj != backend._ffi.NULL
    data = backend._lib.X509_NAME_ENTRY_get_data(x509_name_entry)
    assert data != backend._ffi.NULL
    value = _asn1_string_to_utf8(backend, 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)
        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._ffi.buffer(gn.d.dNSName.data, gn.d.dNSName.length)[:]
        if 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).
            data = 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
            data = idna.decode(data)

        return x509.DNSName(data)
    elif gn.type == backend._lib.GEN_URI:
        data = backend._ffi.buffer(
            gn.d.uniformResourceIdentifier.data,
            gn.d.uniformResourceIdentifier.length
        )[:].decode("ascii")
        parsed = urllib_parse.urlparse(data)
        hostname = idna.decode(parsed.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:
        return x509.IPAddress(
            ipaddress.ip_address(
                backend._ffi.buffer(
                    gn.d.iPAddress.data, gn.d.iPAddress.length
                )[:]
            )
        )
    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._ffi.buffer(
            gn.d.rfc822Name.data, gn.d.rfc822Name.length
        )[:].decode("ascii")
        name, address = parseaddr(data)
        parts = address.split(u"@")
        if name or len(parts) > 2 or not address:
            # parseaddr has found a name (e.g. Name <email>) or the split
            # has found more than 2 parts (which means more than one @ sign)
            # 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])
            )
    else:
        # otherName, 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()


class _X509ExtensionParser(object):
    def __init__(self, ext_count, get_ext, handlers):
        self.ext_count = ext_count
        self.get_ext = get_ext
        self.handlers = handlers

    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)
            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(
                        "{0} is not currently supported".format(oid), oid
                    )
            else:
                value = handler(backend, ext)
                extensions.append(x509.Extension(oid, critical, value))

            seen_oids.add(oid)

        return x509.Extensions(extensions)


@utils.register_interface(x509.Certificate)
class _Certificate(object):
    def __init__(self, backend, x509):
        self._backend = backend
        self._x509 = x509

    def __repr__(self):
        return "<Certificate(subject={0}, ...)>".format(self.subject)

    def __eq__(self, other):
        if not isinstance(other, x509.Certificate):
            return NotImplemented

        res = self._backend._lib.X509_cmp(self._x509, other._x509)
        return res == 0

    def __ne__(self, other):
        return not self == other

    def fingerprint(self, algorithm):
        h = hashes.Hash(algorithm, self._backend)
        bio = self._backend._create_mem_bio()
        res = self._backend._lib.i2d_X509_bio(
            bio, self._x509
        )
        assert res == 1
        der = self._backend._read_mem_bio(bio)
        h.update(der)
        return h.finalize()

    @property
    def version(self):
        version = self._backend._lib.X509_get_version(self._x509)
        if version == 0:
            return x509.Version.v1
        elif version == 2:
            return x509.Version.v3
        else:
            raise x509.InvalidVersion(
                "{0} is not a valid X509 version".format(version), version
            )

    @property
    def serial(self):
        asn1_int = self._backend._lib.X509_get_serialNumber(self._x509)
        assert asn1_int != self._backend._ffi.NULL
        return _asn1_integer_to_int(self._backend, asn1_int)

    def public_key(self):
        pkey = self._backend._lib.X509_get_pubkey(self._x509)
        assert pkey != self._backend._ffi.NULL
        pkey = self._backend._ffi.gc(pkey, self._backend._lib.EVP_PKEY_free)

        return self._backend._evp_pkey_to_public_key(pkey)

    @property
    def not_valid_before(self):
        asn1_time = self._backend._lib.X509_get_notBefore(self._x509)
        return self._parse_asn1_time(asn1_time)

    @property
    def not_valid_after(self):
        asn1_time = self._backend._lib.X509_get_notAfter(self._x509)
        return self._parse_asn1_time(asn1_time)

    def _parse_asn1_time(self, asn1_time):
        assert asn1_time != self._backend._ffi.NULL
        generalized_time = self._backend._lib.ASN1_TIME_to_generalizedtime(
            asn1_time, self._backend._ffi.NULL
        )
        assert generalized_time != self._backend._ffi.NULL
        generalized_time = self._backend._ffi.gc(
            generalized_time, self._backend._lib.ASN1_GENERALIZEDTIME_free
        )
        time = self._backend._ffi.string(
            self._backend._lib.ASN1_STRING_data(
                self._backend._ffi.cast("ASN1_STRING *", generalized_time)
            )
        ).decode("ascii")
        return datetime.datetime.strptime(time, "%Y%m%d%H%M%SZ")

    @property
    def issuer(self):
        issuer = self._backend._lib.X509_get_issuer_name(self._x509)
        assert issuer != self._backend._ffi.NULL
        return _decode_x509_name(self._backend, issuer)

    @property
    def subject(self):
        subject = self._backend._lib.X509_get_subject_name(self._x509)
        assert subject != self._backend._ffi.NULL
        return _decode_x509_name(self._backend, subject)

    @property
    def signature_hash_algorithm(self):
        oid = _obj2txt(self._backend, self._x509.sig_alg.algorithm)
        try:
            return x509._SIG_OIDS_TO_HASH[oid]
        except KeyError:
            raise UnsupportedAlgorithm(
                "Signature algorithm OID:{0} not recognized".format(oid)
            )

    @property
    def extensions(self):
        return _CERTIFICATE_EXTENSION_PARSER.parse(self._backend, self._x509)

    def public_bytes(self, encoding):
        bio = self._backend._create_mem_bio()
        if encoding is serialization.Encoding.PEM:
            res = self._backend._lib.PEM_write_bio_X509(bio, self._x509)
        elif encoding is serialization.Encoding.DER:
            res = self._backend._lib.i2d_X509_bio(bio, self._x509)
        else:
            raise TypeError("encoding must be an item from the Encoding enum")

        assert res == 1
        return self._backend._read_mem_bio(bio)


def _decode_certificate_policies(backend, ext):
    cp = backend._ffi.cast(
        "Cryptography_STACK_OF_POLICYINFO *",
        backend._lib.X509V3_EXT_d2i(ext)
    )
    assert cp != backend._ffi.NULL
    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 == x509.OID_CPS_QUALIFIER:
                    cpsuri = backend._ffi.buffer(
                        pqi.d.cpsuri.data, pqi.d.cpsuri.length
                    )[:].decode('ascii')
                    qualifiers.append(cpsuri)
                elif pqualid == x509.OID_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 = _asn1_string_to_utf8(backend, un.exptext)

    if un.noticeref != backend._ffi.NULL:
        organization = _asn1_string_to_utf8(
            backend, 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 = _asn1_integer_to_int(
                backend, 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, ext):
    bc_st = backend._lib.X509V3_EXT_d2i(ext)
    assert bc_st != backend._ffi.NULL
    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 = _asn1_integer_to_int(
            backend, basic_constraints.pathlen
        )

    return x509.BasicConstraints(ca, path_length)


def _decode_subject_key_identifier(backend, ext):
    asn1_string = backend._lib.X509V3_EXT_d2i(ext)
    assert asn1_string != backend._ffi.NULL
    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, ext):
    akid = backend._lib.X509V3_EXT_d2i(ext)
    assert akid != backend._ffi.NULL
    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 = _asn1_integer_to_int(
            backend, akid.serial
        )

    return x509.AuthorityKeyIdentifier(
        key_identifier, authority_cert_issuer, authority_cert_serial_number
    )


def _decode_authority_information_access(backend, ext):
    aia = backend._lib.X509V3_EXT_d2i(ext)
    assert aia != backend._ffi.NULL
    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)
        assert ad.method != backend._ffi.NULL
        oid = x509.ObjectIdentifier(_obj2txt(backend, ad.method))
        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, ext):
    bit_string = backend._lib.X509V3_EXT_d2i(ext)
    assert bit_string != backend._ffi.NULL
    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, ext):
    gns = backend._ffi.cast(
        "GENERAL_NAMES *", backend._lib.X509V3_EXT_d2i(ext)
    )
    assert gns != backend._ffi.NULL
    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, ext):
    nc = backend._ffi.cast(
        "NAME_CONSTRAINTS *", backend._lib.X509V3_EXT_d2i(ext)
    )
    assert nc != backend._ffi.NULL
    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)
        assert obj != backend._ffi.NULL
        name = _decode_general_name(backend, obj.base)
        subtrees.append(name)

    return subtrees


def _decode_extended_key_usage(backend, ext):
    sk = backend._ffi.cast(
        "Cryptography_STACK_OF_ASN1_OBJECT *",
        backend._lib.X509V3_EXT_d2i(ext)
    )
    assert sk != backend._ffi.NULL
    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)
        assert obj != backend._ffi.NULL
        oid = x509.ObjectIdentifier(_obj2txt(backend, obj))
        ekus.append(oid)

    return x509.ExtendedKeyUsage(ekus)


def _decode_crl_distribution_points(backend, ext):
    cdps = backend._ffi.cast(
        "Cryptography_STACK_OF_DIST_POINT *",
        backend._lib.X509V3_EXT_d2i(ext)
    )
    assert cdps != backend._ffi.NULL
    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 == 0:
                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
                    )
                    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, ext):
    asn1_int = backend._ffi.cast(
        "ASN1_INTEGER *",
        backend._lib.X509V3_EXT_d2i(ext)
    )
    assert asn1_int != backend._ffi.NULL
    asn1_int = backend._ffi.gc(asn1_int, backend._lib.ASN1_INTEGER_free)
    skip_certs = _asn1_integer_to_int(backend, asn1_int)
    return x509.InhibitAnyPolicy(skip_certs)


@utils.register_interface(x509.CertificateSigningRequest)
class _CertificateSigningRequest(object):
    def __init__(self, backend, x509_req):
        self._backend = backend
        self._x509_req = x509_req

    def public_key(self):
        pkey = self._backend._lib.X509_REQ_get_pubkey(self._x509_req)
        assert pkey != self._backend._ffi.NULL
        pkey = self._backend._ffi.gc(pkey, self._backend._lib.EVP_PKEY_free)
        return self._backend._evp_pkey_to_public_key(pkey)

    @property
    def subject(self):
        subject = self._backend._lib.X509_REQ_get_subject_name(self._x509_req)
        assert subject != self._backend._ffi.NULL
        return _decode_x509_name(self._backend, subject)

    @property
    def signature_hash_algorithm(self):
        oid = _obj2txt(self._backend, self._x509_req.sig_alg.algorithm)
        try:
            return x509._SIG_OIDS_TO_HASH[oid]
        except KeyError:
            raise UnsupportedAlgorithm(
                "Signature algorithm OID:{0} not recognized".format(oid)
            )

    @property
    def extensions(self):
        x509_exts = self._backend._lib.X509_REQ_get_extensions(self._x509_req)
        return _CSR_EXTENSION_PARSER.parse(self._backend, x509_exts)

    def public_bytes(self, encoding):
        bio = self._backend._create_mem_bio()
        if encoding is serialization.Encoding.PEM:
            res = self._backend._lib.PEM_write_bio_X509_REQ(
                bio, self._x509_req
            )
        elif encoding is serialization.Encoding.DER:
            res = self._backend._lib.i2d_X509_REQ_bio(bio, self._x509_req)
        else:
            raise TypeError("encoding must be an item from the Encoding enum")

        assert res == 1
        return self._backend._read_mem_bio(bio)


_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={
        x509.OID_BASIC_CONSTRAINTS: _decode_basic_constraints,
        x509.OID_SUBJECT_KEY_IDENTIFIER: _decode_subject_key_identifier,
        x509.OID_KEY_USAGE: _decode_key_usage,
        x509.OID_SUBJECT_ALTERNATIVE_NAME: _decode_subject_alt_name,
        x509.OID_EXTENDED_KEY_USAGE: _decode_extended_key_usage,
        x509.OID_AUTHORITY_KEY_IDENTIFIER: _decode_authority_key_identifier,
        x509.OID_AUTHORITY_INFORMATION_ACCESS: (
            _decode_authority_information_access
        ),
        x509.OID_CERTIFICATE_POLICIES: _decode_certificate_policies,
        x509.OID_CRL_DISTRIBUTION_POINTS: _decode_crl_distribution_points,
        x509.OID_OCSP_NO_CHECK: _decode_ocsp_no_check,
        x509.OID_INHIBIT_ANY_POLICY: _decode_inhibit_any_policy,
        x509.OID_ISSUER_ALTERNATIVE_NAME: _decode_issuer_alt_name,
        x509.OID_NAME_CONSTRAINTS: _decode_name_constraints,
    }
)

_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={
        x509.OID_BASIC_CONSTRAINTS: _decode_basic_constraints,
    }
)