src/cryptography/x509/extensions.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 abc
import hashlib
import ipaddress
from enum import Enum

from pyasn1.codec.der import decoder
from pyasn1.type import namedtype, univ

import six

from cryptography import utils
from cryptography.hazmat.primitives import constant_time, serialization
from cryptography.x509.general_name import GeneralName, IPAddress, OtherName
from cryptography.x509.name import Name
from cryptography.x509.oid import (
    CRLEntryExtensionOID, ExtensionOID, ObjectIdentifier
)


class _SubjectPublicKeyInfo(univ.Sequence):
    componentType = namedtype.NamedTypes(
        namedtype.NamedType('algorithm', univ.Sequence()),
        namedtype.NamedType('subjectPublicKey', univ.BitString())
    )


def _key_identifier_from_public_key(public_key):
    # This is a very slow way to do this.
    serialized = public_key.public_bytes(
        serialization.Encoding.DER,
        serialization.PublicFormat.SubjectPublicKeyInfo
    )
    spki, remaining = decoder.decode(
        serialized, asn1Spec=_SubjectPublicKeyInfo()
    )
    assert not remaining
    # the univ.BitString object is a tuple of bits. We need bytes and
    # pyasn1 really doesn't want to give them to us. To get it we'll
    # build an integer and convert that to bytes.
    bits = 0
    for bit in spki.getComponentByName("subjectPublicKey"):
        bits = bits << 1 | bit

    data = utils.int_to_bytes(bits)
    return hashlib.sha1(data).digest()


class DuplicateExtension(Exception):
    def __init__(self, msg, oid):
        super(DuplicateExtension, self).__init__(msg)
        self.oid = oid


class UnsupportedExtension(Exception):
    def __init__(self, msg, oid):
        super(UnsupportedExtension, self).__init__(msg)
        self.oid = oid


class ExtensionNotFound(Exception):
    def __init__(self, msg, oid):
        super(ExtensionNotFound, self).__init__(msg)
        self.oid = oid


@six.add_metaclass(abc.ABCMeta)
class ExtensionType(object):
    @abc.abstractproperty
    def oid(self):
        """
        Returns the oid associated with the given extension type.
        """


class Extensions(object):
    def __init__(self, extensions):
        self._extensions = extensions

    def get_extension_for_oid(self, oid):
        for ext in self:
            if ext.oid == oid:
                return ext

        raise ExtensionNotFound("No {0} extension was found".format(oid), oid)

    def get_extension_for_class(self, extclass):
        for ext in self:
            if isinstance(ext.value, extclass):
                return ext

        raise ExtensionNotFound(
            "No {0} extension was found".format(extclass), extclass.oid
        )

    def __iter__(self):
        return iter(self._extensions)

    def __len__(self):
        return len(self._extensions)

    def __getitem__(self, idx):
        return self._extensions[idx]

    def __repr__(self):
        return (
            "<Extensions({0})>".format(self._extensions)
        )


@utils.register_interface(ExtensionType)
class CRLNumber(object):
    oid = ExtensionOID.CRL_NUMBER

    def __init__(self, crl_number):
        if not isinstance(crl_number, six.integer_types):
            raise TypeError("crl_number must be an integer")

        self._crl_number = crl_number

    def __eq__(self, other):
        if not isinstance(other, CRLNumber):
            return NotImplemented

        return self.crl_number == other.crl_number

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

    def __repr__(self):
        return "<CRLNumber({0})>".format(self.crl_number)

    crl_number = utils.read_only_property("_crl_number")


@utils.register_interface(ExtensionType)
class AuthorityKeyIdentifier(object):
    oid = ExtensionOID.AUTHORITY_KEY_IDENTIFIER

    def __init__(self, key_identifier, authority_cert_issuer,
                 authority_cert_serial_number):
        if authority_cert_issuer or authority_cert_serial_number:
            if not authority_cert_issuer or not authority_cert_serial_number:
                raise ValueError(
                    "authority_cert_issuer and authority_cert_serial_number "
                    "must both be present or both None"
                )

            if not all(
                isinstance(x, GeneralName) for x in authority_cert_issuer
            ):
                raise TypeError(
                    "authority_cert_issuer must be a list of GeneralName "
                    "objects"
                )

            if not isinstance(authority_cert_serial_number, six.integer_types):
                raise TypeError(
                    "authority_cert_serial_number must be an integer"
                )

        self._key_identifier = key_identifier
        self._authority_cert_issuer = authority_cert_issuer
        self._authority_cert_serial_number = authority_cert_serial_number

    @classmethod
    def from_issuer_public_key(cls, public_key):
        digest = _key_identifier_from_public_key(public_key)
        return cls(
            key_identifier=digest,
            authority_cert_issuer=None,
            authority_cert_serial_number=None
        )

    def __repr__(self):
        return (
            "<AuthorityKeyIdentifier(key_identifier={0.key_identifier!r}, "
            "authority_cert_issuer={0.authority_cert_issuer}, "
            "authority_cert_serial_number={0.authority_cert_serial_number}"
            ")>".format(self)
        )

    def __eq__(self, other):
        if not isinstance(other, AuthorityKeyIdentifier):
            return NotImplemented

        return (
            self.key_identifier == other.key_identifier and
            self.authority_cert_issuer == other.authority_cert_issuer and
            self.authority_cert_serial_number ==
            other.authority_cert_serial_number
        )

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

    key_identifier = utils.read_only_property("_key_identifier")
    authority_cert_issuer = utils.read_only_property("_authority_cert_issuer")
    authority_cert_serial_number = utils.read_only_property(
        "_authority_cert_serial_number"
    )


@utils.register_interface(ExtensionType)
class SubjectKeyIdentifier(object):
    oid = ExtensionOID.SUBJECT_KEY_IDENTIFIER

    def __init__(self, digest):
        self._digest = digest

    @classmethod
    def from_public_key(cls, public_key):
        return cls(_key_identifier_from_public_key(public_key))

    digest = utils.read_only_property("_digest")

    def __repr__(self):
        return "<SubjectKeyIdentifier(digest={0!r})>".format(self.digest)

    def __eq__(self, other):
        if not isinstance(other, SubjectKeyIdentifier):
            return NotImplemented

        return constant_time.bytes_eq(self.digest, other.digest)

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


@utils.register_interface(ExtensionType)
class AuthorityInformationAccess(object):
    oid = ExtensionOID.AUTHORITY_INFORMATION_ACCESS

    def __init__(self, descriptions):
        if not all(isinstance(x, AccessDescription) for x in descriptions):
            raise TypeError(
                "Every item in the descriptions list must be an "
                "AccessDescription"
            )

        self._descriptions = descriptions

    def __iter__(self):
        return iter(self._descriptions)

    def __len__(self):
        return len(self._descriptions)

    def __repr__(self):
        return "<AuthorityInformationAccess({0})>".format(self._descriptions)

    def __eq__(self, other):
        if not isinstance(other, AuthorityInformationAccess):
            return NotImplemented

        return self._descriptions == other._descriptions

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


class AccessDescription(object):
    def __init__(self, access_method, access_location):
        if not isinstance(access_method, ObjectIdentifier):
            raise TypeError("access_method must be an ObjectIdentifier")

        if not isinstance(access_location, GeneralName):
            raise TypeError("access_location must be a GeneralName")

        self._access_method = access_method
        self._access_location = access_location

    def __repr__(self):
        return (
            "<AccessDescription(access_method={0.access_method}, access_locati"
            "on={0.access_location})>".format(self)
        )

    def __eq__(self, other):
        if not isinstance(other, AccessDescription):
            return NotImplemented

        return (
            self.access_method == other.access_method and
            self.access_location == other.access_location
        )

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

    access_method = utils.read_only_property("_access_method")
    access_location = utils.read_only_property("_access_location")


@utils.register_interface(ExtensionType)
class BasicConstraints(object):
    oid = ExtensionOID.BASIC_CONSTRAINTS

    def __init__(self, ca, path_length):
        if not isinstance(ca, bool):
            raise TypeError("ca must be a boolean value")

        if path_length is not None and not ca:
            raise ValueError("path_length must be None when ca is False")

        if (
            path_length is not None and
            (not isinstance(path_length, six.integer_types) or path_length < 0)
        ):
            raise TypeError(
                "path_length must be a non-negative integer or None"
            )

        self._ca = ca
        self._path_length = path_length

    ca = utils.read_only_property("_ca")
    path_length = utils.read_only_property("_path_length")

    def __repr__(self):
        return ("<BasicConstraints(ca={0.ca}, "
                "path_length={0.path_length})>").format(self)

    def __eq__(self, other):
        if not isinstance(other, BasicConstraints):
            return NotImplemented

        return self.ca == other.ca and self.path_length == other.path_length

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


@utils.register_interface(ExtensionType)
class CRLDistributionPoints(object):
    oid = ExtensionOID.CRL_DISTRIBUTION_POINTS

    def __init__(self, distribution_points):
        if not all(
            isinstance(x, DistributionPoint) for x in distribution_points
        ):
            raise TypeError(
                "distribution_points must be a list of DistributionPoint "
                "objects"
            )

        self._distribution_points = distribution_points

    def __iter__(self):
        return iter(self._distribution_points)

    def __len__(self):
        return len(self._distribution_points)

    def __repr__(self):
        return "<CRLDistributionPoints({0})>".format(self._distribution_points)

    def __eq__(self, other):
        if not isinstance(other, CRLDistributionPoints):
            return NotImplemented

        return self._distribution_points == other._distribution_points

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


class DistributionPoint(object):
    def __init__(self, full_name, relative_name, reasons, crl_issuer):
        if full_name and relative_name:
            raise ValueError(
                "You cannot provide both full_name and relative_name, at "
                "least one must be None."
            )

        if full_name and not all(
            isinstance(x, GeneralName) for x in full_name
        ):
            raise TypeError(
                "full_name must be a list of GeneralName objects"
            )

        if relative_name and not isinstance(relative_name, Name):
            raise TypeError("relative_name must be a Name")

        if crl_issuer and not all(
            isinstance(x, GeneralName) for x in crl_issuer
        ):
            raise TypeError(
                "crl_issuer must be None or a list of general names"
            )

        if reasons and (not isinstance(reasons, frozenset) or not all(
            isinstance(x, ReasonFlags) for x in reasons
        )):
            raise TypeError("reasons must be None or frozenset of ReasonFlags")

        if reasons and (
            ReasonFlags.unspecified in reasons or
            ReasonFlags.remove_from_crl in reasons
        ):
            raise ValueError(
                "unspecified and remove_from_crl are not valid reasons in a "
                "DistributionPoint"
            )

        if reasons and not crl_issuer and not (full_name or relative_name):
            raise ValueError(
                "You must supply crl_issuer, full_name, or relative_name when "
                "reasons is not None"
            )

        self._full_name = full_name
        self._relative_name = relative_name
        self._reasons = reasons
        self._crl_issuer = crl_issuer

    def __repr__(self):
        return (
            "<DistributionPoint(full_name={0.full_name}, relative_name={0.rela"
            "tive_name}, reasons={0.reasons}, crl_issuer={0.crl_is"
            "suer})>".format(self)
        )

    def __eq__(self, other):
        if not isinstance(other, DistributionPoint):
            return NotImplemented

        return (
            self.full_name == other.full_name and
            self.relative_name == other.relative_name and
            self.reasons == other.reasons and
            self.crl_issuer == other.crl_issuer
        )

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

    full_name = utils.read_only_property("_full_name")
    relative_name = utils.read_only_property("_relative_name")
    reasons = utils.read_only_property("_reasons")
    crl_issuer = utils.read_only_property("_crl_issuer")


class ReasonFlags(Enum):
    unspecified = "unspecified"
    key_compromise = "keyCompromise"
    ca_compromise = "cACompromise"
    affiliation_changed = "affiliationChanged"
    superseded = "superseded"
    cessation_of_operation = "cessationOfOperation"
    certificate_hold = "certificateHold"
    privilege_withdrawn = "privilegeWithdrawn"
    aa_compromise = "aACompromise"
    remove_from_crl = "removeFromCRL"


@utils.register_interface(ExtensionType)
class CertificatePolicies(object):
    oid = ExtensionOID.CERTIFICATE_POLICIES

    def __init__(self, policies):
        if not all(isinstance(x, PolicyInformation) for x in policies):
            raise TypeError(
                "Every item in the policies list must be a "
                "PolicyInformation"
            )

        self._policies = policies

    def __iter__(self):
        return iter(self._policies)

    def __len__(self):
        return len(self._policies)

    def __repr__(self):
        return "<CertificatePolicies({0})>".format(self._policies)

    def __eq__(self, other):
        if not isinstance(other, CertificatePolicies):
            return NotImplemented

        return self._policies == other._policies

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


class PolicyInformation(object):
    def __init__(self, policy_identifier, policy_qualifiers):
        if not isinstance(policy_identifier, ObjectIdentifier):
            raise TypeError("policy_identifier must be an ObjectIdentifier")

        self._policy_identifier = policy_identifier
        if policy_qualifiers and not all(
            isinstance(
                x, (six.text_type, UserNotice)
            ) for x in policy_qualifiers
        ):
            raise TypeError(
                "policy_qualifiers must be a list of strings and/or UserNotice"
                " objects or None"
            )

        self._policy_qualifiers = policy_qualifiers

    def __repr__(self):
        return (
            "<PolicyInformation(policy_identifier={0.policy_identifier}, polic"
            "y_qualifiers={0.policy_qualifiers})>".format(self)
        )

    def __eq__(self, other):
        if not isinstance(other, PolicyInformation):
            return NotImplemented

        return (
            self.policy_identifier == other.policy_identifier and
            self.policy_qualifiers == other.policy_qualifiers
        )

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

    policy_identifier = utils.read_only_property("_policy_identifier")
    policy_qualifiers = utils.read_only_property("_policy_qualifiers")


class UserNotice(object):
    def __init__(self, notice_reference, explicit_text):
        if notice_reference and not isinstance(
            notice_reference, NoticeReference
        ):
            raise TypeError(
                "notice_reference must be None or a NoticeReference"
            )

        self._notice_reference = notice_reference
        self._explicit_text = explicit_text

    def __repr__(self):
        return (
            "<UserNotice(notice_reference={0.notice_reference}, explicit_text="
            "{0.explicit_text!r})>".format(self)
        )

    def __eq__(self, other):
        if not isinstance(other, UserNotice):
            return NotImplemented

        return (
            self.notice_reference == other.notice_reference and
            self.explicit_text == other.explicit_text
        )

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

    notice_reference = utils.read_only_property("_notice_reference")
    explicit_text = utils.read_only_property("_explicit_text")


class NoticeReference(object):
    def __init__(self, organization, notice_numbers):
        self._organization = organization
        if not isinstance(notice_numbers, list) or not all(
            isinstance(x, int) for x in notice_numbers
        ):
            raise TypeError(
                "notice_numbers must be a list of integers"
            )

        self._notice_numbers = notice_numbers

    def __repr__(self):
        return (
            "<NoticeReference(organization={0.organization!r}, notice_numbers="
            "{0.notice_numbers})>".format(self)
        )

    def __eq__(self, other):
        if not isinstance(other, NoticeReference):
            return NotImplemented

        return (
            self.organization == other.organization and
            self.notice_numbers == other.notice_numbers
        )

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

    organization = utils.read_only_property("_organization")
    notice_numbers = utils.read_only_property("_notice_numbers")


@utils.register_interface(ExtensionType)
class ExtendedKeyUsage(object):
    oid = ExtensionOID.EXTENDED_KEY_USAGE

    def __init__(self, usages):
        if not all(isinstance(x, ObjectIdentifier) for x in usages):
            raise TypeError(
                "Every item in the usages list must be an ObjectIdentifier"
            )

        self._usages = usages

    def __iter__(self):
        return iter(self._usages)

    def __len__(self):
        return len(self._usages)

    def __repr__(self):
        return "<ExtendedKeyUsage({0})>".format(self._usages)

    def __eq__(self, other):
        if not isinstance(other, ExtendedKeyUsage):
            return NotImplemented

        return self._usages == other._usages

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


@utils.register_interface(ExtensionType)
class OCSPNoCheck(object):
    oid = ExtensionOID.OCSP_NO_CHECK


@utils.register_interface(ExtensionType)
class InhibitAnyPolicy(object):
    oid = ExtensionOID.INHIBIT_ANY_POLICY

    def __init__(self, skip_certs):
        if not isinstance(skip_certs, six.integer_types):
            raise TypeError("skip_certs must be an integer")

        if skip_certs < 0:
            raise ValueError("skip_certs must be a non-negative integer")

        self._skip_certs = skip_certs

    def __repr__(self):
        return "<InhibitAnyPolicy(skip_certs={0.skip_certs})>".format(self)

    def __eq__(self, other):
        if not isinstance(other, InhibitAnyPolicy):
            return NotImplemented

        return self.skip_certs == other.skip_certs

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

    skip_certs = utils.read_only_property("_skip_certs")


@utils.register_interface(ExtensionType)
class KeyUsage(object):
    oid = ExtensionOID.KEY_USAGE

    def __init__(self, digital_signature, content_commitment, key_encipherment,
                 data_encipherment, key_agreement, key_cert_sign, crl_sign,
                 encipher_only, decipher_only):
        if not key_agreement and (encipher_only or decipher_only):
            raise ValueError(
                "encipher_only and decipher_only can only be true when "
                "key_agreement is true"
            )

        self._digital_signature = digital_signature
        self._content_commitment = content_commitment
        self._key_encipherment = key_encipherment
        self._data_encipherment = data_encipherment
        self._key_agreement = key_agreement
        self._key_cert_sign = key_cert_sign
        self._crl_sign = crl_sign
        self._encipher_only = encipher_only
        self._decipher_only = decipher_only

    digital_signature = utils.read_only_property("_digital_signature")
    content_commitment = utils.read_only_property("_content_commitment")
    key_encipherment = utils.read_only_property("_key_encipherment")
    data_encipherment = utils.read_only_property("_data_encipherment")
    key_agreement = utils.read_only_property("_key_agreement")
    key_cert_sign = utils.read_only_property("_key_cert_sign")
    crl_sign = utils.read_only_property("_crl_sign")

    @property
    def encipher_only(self):
        if not self.key_agreement:
            raise ValueError(
                "encipher_only is undefined unless key_agreement is true"
            )
        else:
            return self._encipher_only

    @property
    def decipher_only(self):
        if not self.key_agreement:
            raise ValueError(
                "decipher_only is undefined unless key_agreement is true"
            )
        else:
            return self._decipher_only

    def __repr__(self):
        try:
            encipher_only = self.encipher_only
            decipher_only = self.decipher_only
        except ValueError:
            encipher_only = None
            decipher_only = None

        return ("<KeyUsage(digital_signature={0.digital_signature}, "
                "content_commitment={0.content_commitment}, "
                "key_encipherment={0.key_encipherment}, "
                "data_encipherment={0.data_encipherment}, "
                "key_agreement={0.key_agreement}, "
                "key_cert_sign={0.key_cert_sign}, crl_sign={0.crl_sign}, "
                "encipher_only={1}, decipher_only={2})>").format(
                    self, encipher_only, decipher_only)

    def __eq__(self, other):
        if not isinstance(other, KeyUsage):
            return NotImplemented

        return (
            self.digital_signature == other.digital_signature and
            self.content_commitment == other.content_commitment and
            self.key_encipherment == other.key_encipherment and
            self.data_encipherment == other.data_encipherment and
            self.key_agreement == other.key_agreement and
            self.key_cert_sign == other.key_cert_sign and
            self.crl_sign == other.crl_sign and
            self._encipher_only == other._encipher_only and
            self._decipher_only == other._decipher_only
        )

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


@utils.register_interface(ExtensionType)
class NameConstraints(object):
    oid = ExtensionOID.NAME_CONSTRAINTS

    def __init__(self, permitted_subtrees, excluded_subtrees):
        if permitted_subtrees is not None:
            if not all(
                isinstance(x, GeneralName) for x in permitted_subtrees
            ):
                raise TypeError(
                    "permitted_subtrees must be a list of GeneralName objects "
                    "or None"
                )

            self._validate_ip_name(permitted_subtrees)

        if excluded_subtrees is not None:
            if not all(
                isinstance(x, GeneralName) for x in excluded_subtrees
            ):
                raise TypeError(
                    "excluded_subtrees must be a list of GeneralName objects "
                    "or None"
                )

            self._validate_ip_name(excluded_subtrees)

        if permitted_subtrees is None and excluded_subtrees is None:
            raise ValueError(
                "At least one of permitted_subtrees and excluded_subtrees "
                "must not be None"
            )

        self._permitted_subtrees = permitted_subtrees
        self._excluded_subtrees = excluded_subtrees

    def __eq__(self, other):
        if not isinstance(other, NameConstraints):
            return NotImplemented

        return (
            self.excluded_subtrees == other.excluded_subtrees and
            self.permitted_subtrees == other.permitted_subtrees
        )

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

    def _validate_ip_name(self, tree):
        if any(isinstance(name, IPAddress) and not isinstance(
            name.value, (ipaddress.IPv4Network, ipaddress.IPv6Network)
        ) for name in tree):
            raise TypeError(
                "IPAddress name constraints must be an IPv4Network or"
                " IPv6Network object"
            )

    def __repr__(self):
        return (
            u"<NameConstraints(permitted_subtrees={0.permitted_subtrees}, "
            u"excluded_subtrees={0.excluded_subtrees})>".format(self)
        )

    permitted_subtrees = utils.read_only_property("_permitted_subtrees")
    excluded_subtrees = utils.read_only_property("_excluded_subtrees")


class Extension(object):
    def __init__(self, oid, critical, value):
        if not isinstance(oid, ObjectIdentifier):
            raise TypeError(
                "oid argument must be an ObjectIdentifier instance."
            )

        if not isinstance(critical, bool):
            raise TypeError("critical must be a boolean value")

        self._oid = oid
        self._critical = critical
        self._value = value

    oid = utils.read_only_property("_oid")
    critical = utils.read_only_property("_critical")
    value = utils.read_only_property("_value")

    def __repr__(self):
        return ("<Extension(oid={0.oid}, critical={0.critical}, "
                "value={0.value})>").format(self)

    def __eq__(self, other):
        if not isinstance(other, Extension):
            return NotImplemented

        return (
            self.oid == other.oid and
            self.critical == other.critical and
            self.value == other.value
        )

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


class GeneralNames(object):
    def __init__(self, general_names):
        if not all(isinstance(x, GeneralName) for x in general_names):
            raise TypeError(
                "Every item in the general_names list must be an "
                "object conforming to the GeneralName interface"
            )

        self._general_names = general_names

    def __iter__(self):
        return iter(self._general_names)

    def __len__(self):
        return len(self._general_names)

    def get_values_for_type(self, type):
        # Return the value of each GeneralName, except for OtherName instances
        # which we return directly because it has two important properties not
        # just one value.
        objs = (i for i in self if isinstance(i, type))
        if type != OtherName:
            objs = (i.value for i in objs)
        return list(objs)

    def __repr__(self):
        return "<GeneralNames({0})>".format(self._general_names)

    def __eq__(self, other):
        if not isinstance(other, GeneralNames):
            return NotImplemented

        return self._general_names == other._general_names

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


@utils.register_interface(ExtensionType)
class SubjectAlternativeName(object):
    oid = ExtensionOID.SUBJECT_ALTERNATIVE_NAME

    def __init__(self, general_names):
        self._general_names = GeneralNames(general_names)

    def __iter__(self):
        return iter(self._general_names)

    def __len__(self):
        return len(self._general_names)

    def get_values_for_type(self, type):
        return self._general_names.get_values_for_type(type)

    def __repr__(self):
        return "<SubjectAlternativeName({0})>".format(self._general_names)

    def __eq__(self, other):
        if not isinstance(other, SubjectAlternativeName):
            return NotImplemented

        return self._general_names == other._general_names

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


@utils.register_interface(ExtensionType)
class IssuerAlternativeName(object):
    oid = ExtensionOID.ISSUER_ALTERNATIVE_NAME

    def __init__(self, general_names):
        self._general_names = GeneralNames(general_names)

    def __iter__(self):
        return iter(self._general_names)

    def __len__(self):
        return len(self._general_names)

    def get_values_for_type(self, type):
        return self._general_names.get_values_for_type(type)

    def __repr__(self):
        return "<IssuerAlternativeName({0})>".format(self._general_names)

    def __eq__(self, other):
        if not isinstance(other, IssuerAlternativeName):
            return NotImplemented

        return self._general_names == other._general_names

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


@utils.register_interface(ExtensionType)
class CertificateIssuer(object):
    oid = CRLEntryExtensionOID.CERTIFICATE_ISSUER

    def __init__(self, general_names):
        self._general_names = GeneralNames(general_names)

    def __iter__(self):
        return iter(self._general_names)

    def __len__(self):
        return len(self._general_names)

    def get_values_for_type(self, type):
        return self._general_names.get_values_for_type(type)

    def __repr__(self):
        return "<CertificateIssuer({0})>".format(self._general_names)

    def __eq__(self, other):
        if not isinstance(other, CertificateIssuer):
            return NotImplemented

        return self._general_names == other._general_names

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


@utils.register_interface(ExtensionType)
class CRLReason(object):
    oid = CRLEntryExtensionOID.CRL_REASON

    def __init__(self, reason):
        if not isinstance(reason, ReasonFlags):
            raise TypeError("reason must be an element from ReasonFlags")

        self._reason = reason

    def __repr__(self):
        return "<CRLReason(reason={0})>".format(self._reason)

    def __eq__(self, other):
        if not isinstance(other, CRLReason):
            return NotImplemented

        return self.reason == other.reason

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

    reason = utils.read_only_property("_reason")