docs/x509.rst

X.509
=====

.. currentmodule:: cryptography.x509

.. testsetup::

    pem_req_data = b"""
    -----BEGIN CERTIFICATE REQUEST-----
    MIIC0zCCAbsCAQAwWTELMAkGA1UEBhMCVVMxETAPBgNVBAgMCElsbGlub2lzMRAw
    DgYDVQQHDAdDaGljYWdvMREwDwYDVQQKDAhyNTA5IExMQzESMBAGA1UEAwwJaGVs
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    5wFkeYsZEA==
    -----END CERTIFICATE REQUEST-----
    """.strip()

    pem_data = b"""
    -----BEGIN CERTIFICATE-----
    MIIDfDCCAmSgAwIBAgIBAjANBgkqhkiG9w0BAQsFADBFMQswCQYDVQQGEwJVUzEf
    MB0GA1UEChMWVGVzdCBDZXJ0aWZpY2F0ZXMgMjAxMTEVMBMGA1UEAxMMVHJ1c3Qg
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    QYw2jOvpKcKtWCSAnegEbgsGYzATKjmPJPJ0npHFqzM=
    -----END CERTIFICATE-----
    """.strip()

    cryptography_cert_pem = b"""
    -----BEGIN CERTIFICATE-----
    MIIFvTCCBKWgAwIBAgICPyAwDQYJKoZIhvcNAQELBQAwRzELMAkGA1UEBhMCVVMx
    FjAUBgNVBAoTDUdlb1RydXN0IEluYy4xIDAeBgNVBAMTF1JhcGlkU1NMIFNIQTI1
    NiBDQSAtIEczMB4XDTE0MTAxNTEyMDkzMloXDTE4MTExNjAxMTUwM1owgZcxEzAR
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    BggrBgEFBQcDAjAvBgNVHREEKDAmghN3d3cuY3J5cHRvZ3JhcGh5Lmlvgg9jcnlw
    dG9ncmFwaHkuaW8wKwYDVR0fBCQwIjAgoB6gHIYaaHR0cDovL2d2LnN5bWNiLmNv
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    LDAqBggrBgEFBQcCARYeaHR0cHM6Ly93d3cucmFwaWRzc2wuY29tL2xlZ2FsMA0G
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    Xlt2dp2nDQuwGyK2vB7dMfKnQAkxwq1sYUXznB8i0IhhCAoXp01QGPKq51YoIlnF
    7DRMk6iEaL1SJbkIrLsCQyZFDf0xtfW9DqXugMMLoxeCsBhZJQzNyS2ryirrv9LH
    aK3+6IZjrcyy9bkpz/gzJucyhU+75c4My/mnRCrtItRbCQuiI5pd5poDowm+HH9i
    GVI9+0lAFwxOUnOnwsoI40iOoxjLMGB+CgFLKCGUcWxP
    -----END CERTIFICATE-----
    """.strip()

X.509 is an ITU-T standard for a `public key infrastructure`_. X.509v3 is
defined in :rfc:`5280` (which obsoletes :rfc:`2459` and :rfc:`3280`). X.509
certificates are commonly used in protocols like `TLS`_.

Loading Certificates
~~~~~~~~~~~~~~~~~~~~

.. function:: load_pem_x509_certificate(data, backend)

    .. versionadded:: 0.7

    Deserialize a certificate from PEM encoded data. PEM certificates are
    base64 decoded and have delimiters that look like
    ``-----BEGIN CERTIFICATE-----``.

    :param bytes data: The PEM encoded certificate data.

    :param backend: A backend supporting the
        :class:`~cryptography.hazmat.backends.interfaces.X509Backend`
        interface.

    :returns: An instance of :class:`~cryptography.x509.Certificate`.

.. function:: load_der_x509_certificate(data, backend)

    .. versionadded:: 0.7

    Deserialize a certificate from DER encoded data. DER is a binary format
    and is commonly found in files with the ``.cer`` extension (although file
    extensions are not a guarantee of encoding type).

    :param bytes data: The DER encoded certificate data.

    :param backend: A backend supporting the
        :class:`~cryptography.hazmat.backends.interfaces.X509Backend`
        interface.

    :returns: An instance of :class:`~cryptography.x509.Certificate`.

.. doctest::

    >>> from cryptography import x509
    >>> from cryptography.hazmat.backends import default_backend
    >>> cert = x509.load_pem_x509_certificate(pem_data, default_backend())
    >>> cert.serial
    2

Loading Certificate Signing Requests
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. function:: load_pem_x509_csr(data, backend)

    .. versionadded:: 0.9

    Deserialize a certificate signing request (CSR) from PEM encoded data. PEM
    requests are base64 decoded and have delimiters that look like
    ``-----BEGIN CERTIFICATE REQUEST-----``. This format is also known as
    PKCS#10.

    :param bytes data: The PEM encoded request data.

    :param backend: A backend supporting the
        :class:`~cryptography.hazmat.backends.interfaces.X509Backend`
        interface.

    :returns: An instance of
        :class:`~cryptography.x509.CertificateSigningRequest`.

.. function:: load_der_x509_csr(data, backend)

    .. versionadded:: 0.9

    Deserialize a certificate signing request (CSR) from DER encoded data. DER
    is a binary format and is not commonly used with CSRs.

    :param bytes data: The DER encoded request data.

    :param backend: A backend supporting the
        :class:`~cryptography.hazmat.backends.interfaces.X509Backend`
        interface.

    :returns: An instance of
        :class:`~cryptography.x509.CertificateSigningRequest`.

.. doctest::

    >>> from cryptography import x509
    >>> from cryptography.hazmat.backends import default_backend
    >>> from cryptography.hazmat.primitives import hashes
    >>> csr = x509.load_pem_x509_csr(pem_req_data, default_backend())
    >>> isinstance(csr.signature_hash_algorithm, hashes.SHA1)
    True

X.509 Certificate Object
~~~~~~~~~~~~~~~~~~~~~~~~

.. class:: Certificate

    .. versionadded:: 0.7

    .. attribute:: version

        :type: :class:`~cryptography.x509.Version`

        The certificate version as an enumeration. Version 3 certificates are
        the latest version and also the only type you should see in practice.

        :raises cryptography.x509.InvalidVersion: If the version in the
            certificate is not a known
            :class:`X.509 version <cryptography.x509.Version>`.

        .. doctest::

            >>> cert.version
            <Version.v3: 2>

    .. method:: fingerprint(algorithm)

        :param algorithm: The
            :class:`~cryptography.hazmat.primitives.hashes.HashAlgorithm`
            that will be used to generate the fingerprint.

        :return bytes: The fingerprint using the supplied hash algorithm as
            bytes.

        .. doctest::

            >>> from cryptography.hazmat.primitives import hashes
            >>> cert.fingerprint(hashes.SHA256())
            '\x86\xd2\x187Gc\xfc\xe7}[+E9\x8d\xb4\x8f\x10\xe5S\xda\x18u\xbe}a\x03\x08[\xac\xa04?'

    .. attribute:: serial

        :type: int

        The serial as a Python integer.

        .. doctest::

            >>> cert.serial
            2

    .. method:: public_key()

        :type:
            :class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKey` or
            :class:`~cryptography.hazmat.primitives.asymmetric.dsa.DSAPublicKey` or
            :class:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey`

        The public key associated with the certificate.

        .. doctest::

            >>> from cryptography.hazmat.primitives.asymmetric import rsa
            >>> public_key = cert.public_key()
            >>> isinstance(public_key, rsa.RSAPublicKey)
            True

    .. attribute:: not_valid_before

        :type: :class:`datetime.datetime`

        A naïve datetime representing the beginning of the validity period for
        the certificate in UTC. This value is inclusive.

        .. doctest::

            >>> cert.not_valid_before
            datetime.datetime(2010, 1, 1, 8, 30)

    .. attribute:: not_valid_after

        :type: :class:`datetime.datetime`

        A naïve datetime representing the end of the validity period for the
        certificate in UTC. This value is inclusive.

        .. doctest::

            >>> cert.not_valid_after
            datetime.datetime(2030, 12, 31, 8, 30)

    .. attribute:: issuer

        .. versionadded:: 0.8

        :type: :class:`Name`

        The :class:`Name` of the issuer.

    .. attribute:: subject

        .. versionadded:: 0.8

        :type: :class:`Name`

        The :class:`Name` of the subject.

    .. attribute:: signature_hash_algorithm

        :type: :class:`~cryptography.hazmat.primitives.hashes.HashAlgorithm`

        Returns the
        :class:`~cryptography.hazmat.primitives.hashes.HashAlgorithm` which
        was used in signing this certificate.

        .. doctest::

            >>> from cryptography.hazmat.primitives import hashes
            >>> isinstance(cert.signature_hash_algorithm, hashes.SHA256)
            True

    .. attribute:: extensions

        :type: :class:`Extensions`

        The extensions encoded in the certificate.

        :raises cryptography.x509.DuplicateExtension: If more than one
            extension of the same type is found within the certificate.

        :raises cryptography.x509.UnsupportedExtension: If the certificate
            contains an extension that is not supported.

        :raises cryptography.x509.UnsupportedGeneralNameType: If an extension
            contains a general name that is not supported.

        .. doctest::

            >>> for ext in cert.extensions:
            ...     print(ext)
            <Extension(oid=<ObjectIdentifier(oid=2.5.29.35, name=authorityKeyIdentifier)>, critical=False, value=<AuthorityKeyIdentifier(key_identifier='\xe4}_\xd1\\\x95\x86\x08,\x05\xae\xbeu\xb6e\xa7\xd9]\xa8f', authority_cert_issuer=None, authority_cert_serial_number=None)>)>
            <Extension(oid=<ObjectIdentifier(oid=2.5.29.14, name=subjectKeyIdentifier)>, critical=False, value=<SubjectKeyIdentifier(digest='X\x01\x84$\x1b\xbc+R\x94J=\xa5\x10r\x14Q\xf5\xaf:\xc9')>)>
            <Extension(oid=<ObjectIdentifier(oid=2.5.29.15, name=keyUsage)>, critical=True, value=<KeyUsage(digital_signature=False, content_commitment=False, key_encipherment=False, data_encipherment=False, key_agreement=False, key_cert_sign=True, crl_sign=True, encipher_only=None, decipher_only=None)>)>
            <Extension(oid=<ObjectIdentifier(oid=2.5.29.32, name=certificatePolicies)>, critical=False, value=<CertificatePolicies([<PolicyInformation(policy_identifier=<ObjectIdentifier(oid=2.16.840.1.101.3.2.1.48.1, name=Unknown OID)>, policy_qualifiers=None)>])>)>
            <Extension(oid=<ObjectIdentifier(oid=2.5.29.19, name=basicConstraints)>, critical=True, value=<BasicConstraints(ca=True, path_length=None)>)>

X.509 CSR (Certificate Signing Request) Object
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. class:: CertificateSigningRequest

    .. versionadded:: 0.9

    .. method:: public_key()

        :type:
            :class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKey` or
            :class:`~cryptography.hazmat.primitives.asymmetric.dsa.DSAPublicKey` or
            :class:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey`

        The public key associated with the request.

        .. doctest::

            >>> from cryptography.hazmat.primitives.asymmetric import rsa
            >>> public_key = csr.public_key()
            >>> isinstance(public_key, rsa.RSAPublicKey)
            True

    .. attribute:: subject

        :type: :class:`Name`

        The :class:`Name` of the subject.

    .. attribute:: signature_hash_algorithm

        :type: :class:`~cryptography.hazmat.primitives.hashes.HashAlgorithm`

        Returns the
        :class:`~cryptography.hazmat.primitives.hashes.HashAlgorithm` which
        was used in signing this request.

        .. doctest::

            >>> from cryptography.hazmat.primitives import hashes
            >>> isinstance(csr.signature_hash_algorithm, hashes.SHA1)
            True

    .. method:: public_bytes(encoding)

        :param encoding: The
            :class:`~cryptography.hazmat.primitives.serialization.Encoding`
            that will be used to serialize the certificate request.

        :return bytes: The data that can be written to a file or sent
            over the network to be signed by the certificate
            authority.


.. class:: Name

    .. versionadded:: 0.8

    An X509 Name is an ordered list of attributes. The object is iterable to
    get every attribute or you can use :meth:`Name.get_attributes_for_oid` to
    obtain the specific type you want. Names are sometimes represented as a
    slash or comma delimited string (e.g. ``/CN=mydomain.com/O=My Org/C=US`` or
    ``CN=mydomain.com, O=My Org, C=US``).

    .. doctest::

        >>> len(cert.subject)
        3
        >>> for attribute in cert.subject:
        ...     print(attribute)
        <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.6, name=countryName)>, value=u'US')>
        <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.10, name=organizationName)>, value=u'Test Certificates 2011')>
        <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.3, name=commonName)>, value=u'Good CA')>

    .. method:: get_attributes_for_oid(oid)

        :param oid: An :class:`ObjectIdentifier` instance.

        :returns: A list of :class:`NameAttribute` instances that match the
            OID provided. If nothing matches an empty list will be returned.

        .. doctest::

            >>> cert.subject.get_attributes_for_oid(x509.OID_COMMON_NAME)
            [<NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.3, name=commonName)>, value=u'Good CA')>]

.. class:: Version

    .. versionadded:: 0.7

    An enumeration for X.509 versions.

    .. attribute:: v1

        For version 1 X.509 certificates.

    .. attribute:: v3

        For version 3 X.509 certificates.

.. class:: NameAttribute

    .. versionadded:: 0.8

    An X.509 name consists of a list of NameAttribute instances.

    .. attribute:: oid

        :type: :class:`ObjectIdentifier`

        The attribute OID.

    .. attribute:: value

        :type: :term:`text`

        The value of the attribute.

.. class:: ObjectIdentifier

    .. versionadded:: 0.8

    Object identifiers (frequently seen abbreviated as OID) identify the type
    of a value (see: :class:`NameAttribute`).

    .. attribute:: dotted_string

        :type: :class:`str`

        The dotted string value of the OID (e.g. ``"2.5.4.3"``)

.. _general_name_classes:

General Name Classes
~~~~~~~~~~~~~~~~~~~~

.. class:: GeneralName

    .. versionadded:: 0.9

    This is the generic interface that all the following classes are registered
    against.

.. class:: RFC822Name

    .. versionadded:: 0.9

    This corresponds to an email address. For example, ``user@example.com``.

    .. attribute:: value

        :type: :term:`text`

.. class:: DNSName

    .. versionadded:: 0.9

    This corresponds to a domain name. For example, ``cryptography.io``.

    .. attribute:: value

        :type: :term:`text`

.. class:: DirectoryName

    .. versionadded:: 0.9

    This corresponds to a directory name.

    .. attribute:: value

        :type: :class:`Name`

.. class:: UniformResourceIdentifier

    .. versionadded:: 0.9

    This corresponds to a uniform resource identifier.  For example,
    ``https://cryptography.io``. The URI is parsed and IDNA decoded (see
    :rfc:`5895`).

    .. note::

        URIs that do not contain ``://`` in them will not be decoded.

    .. attribute:: value

        :type: :term:`text`

.. class:: IPAddress

    .. versionadded:: 0.9

    This corresponds to an IP address.

    .. attribute:: value

        :type: :class:`~ipaddress.IPv4Address`,
            :class:`~ipaddress.IPv6Address`,  :class:`~ipaddress.IPv4Network`,
            or :class:`~ipaddress.IPv6Network`.

.. class:: RegisteredID

    .. versionadded:: 0.9

    This corresponds to a registered ID.

    .. attribute:: value

        :type: :class:`ObjectIdentifier`

X.509 Extensions
~~~~~~~~~~~~~~~~

.. class:: Extensions

    .. versionadded:: 0.9

    An X.509 Extensions instance is an ordered list of extensions.  The object
    is iterable to get every extension.

    .. method:: get_extension_for_oid(oid)

        :param oid: An :class:`ObjectIdentifier` instance.

        :returns: An instance of the extension class.

        :raises cryptography.x509.ExtensionNotFound: If the certificate does
            not have the extension requested.

        .. doctest::

            >>> cert.extensions.get_extension_for_oid(x509.OID_BASIC_CONSTRAINTS)
            <Extension(oid=<ObjectIdentifier(oid=2.5.29.19, name=basicConstraints)>, critical=True, value=<BasicConstraints(ca=True, path_length=None)>)>

.. class:: Extension

    .. versionadded:: 0.9

    .. attribute:: oid

        :type: :class:`ObjectIdentifier`

        The :ref:`extension OID <extension_oids>`.

    .. attribute:: critical

        :type: bool

        Determines whether a given extension is critical or not. :rfc:`5280`
        requires that "A certificate-using system MUST reject the certificate
        if it encounters a critical extension it does not recognize or a
        critical extension that contains information that it cannot process".

    .. attribute:: value

        Returns an instance of the extension type corresponding to the OID.

.. class:: KeyUsage

    .. versionadded:: 0.9

    The key usage extension defines the purpose of the key contained in the
    certificate.  The usage restriction might be employed when a key that could
    be used for more than one operation is to be restricted. It corresponds to
    :data:`OID_KEY_USAGE`.

    .. attribute:: digital_signature

        :type: bool

        This purpose is set to true when the subject public key is used for verifying
        digital signatures, other than signatures on certificates
        (``key_cert_sign``) and CRLs (``crl_sign``).

    .. attribute:: content_commitment

        :type: bool

        This purpose is set to true when the subject public key is used for verifying
        digital signatures, other than signatures on certificates
        (``key_cert_sign``) and CRLs (``crl_sign``). It is used to provide a
        non-repudiation service that protects against the signing entity
        falsely denying some action. In the case of later conflict, a
        reliable third party may determine the authenticity of the signed
        data. This was called ``non_repudiation`` in older revisions of the
        X.509 specification.

    .. attribute:: key_encipherment

        :type: bool

        This purpose is set to true when the subject public key is used for
        enciphering private or secret keys.

    .. attribute:: data_encipherment

        :type: bool

        This purpose is set to true when the subject public key is used for
        directly enciphering raw user data without the use of an intermediate
        symmetric cipher.

    .. attribute:: key_agreement

        :type: bool

        This purpose is set to true when the subject public key is used for key
        agreement.  For example, when a Diffie-Hellman key is to be used for
        key management, then this purpose is set to true.

    .. attribute:: key_cert_sign

        :type: bool

        This purpose is set to true when the subject public key is used for
        verifying signatures on public key certificates. If this purpose is set
        to true then ``ca`` must be true in the :class:`BasicConstraints`
        extension.

    .. attribute:: crl_sign

        :type: bool

        This purpose is set to true when the subject public key is used for
        verifying signatures on certificate revocation lists.

    .. attribute:: encipher_only

        :type: bool

        When this purposes is set to true and the ``key_agreement`` purpose is
        also set, the subject public key may be used only for enciphering data
        while performing key agreement.

        :raises ValueError: This is raised if accessed when ``key_agreement``
            is false.

    .. attribute:: decipher_only

        :type: bool

        When this purposes is set to true and the ``key_agreement`` purpose is
        also set, the subject public key may be used only for deciphering data
        while performing key agreement.

        :raises ValueError: This is raised if accessed when ``key_agreement``
            is false.


.. class:: BasicConstraints

    .. versionadded:: 0.9

    Basic constraints is an X.509 extension type that defines whether a given
    certificate is allowed to sign additional certificates and what path
    length restrictions may exist. It corresponds to
    :data:`OID_BASIC_CONSTRAINTS`.

    .. attribute:: ca

        :type: bool

        Whether the certificate can sign certificates.

    .. attribute:: path_length

        :type: int or None

        The maximum path length for certificates subordinate to this
        certificate. This attribute only has meaning if ``ca`` is true.
        If ``ca`` is true then a path length of None means there's no
        restriction on the number of subordinate CAs in the certificate chain.
        If it is zero or greater then it defines the maximum length for a
        subordinate CA's certificate chain. For example, a ``path_length`` of 1
        means the certificate can sign a subordinate CA, but the subordinate CA
        is not allowed to create subordinates with ``ca`` set to true.

.. class:: ExtendedKeyUsage

    .. versionadded:: 0.9

    This extension indicates one or more purposes for which the certified
    public key may be used, in addition to or in place of the basic
    purposes indicated in the key usage extension. The object is
    iterable to obtain the list of :ref:`extended key usage OIDs <eku_oids>`.

.. class:: OCSPNoCheck

    .. versionadded:: 0.10

    This presence of this extension indicates that an OCSP client can trust a
    responder for the lifetime of the responder's certificate. CAs issuing
    such a certificate should realize that a compromise of the responder's key
    is as serious as the compromise of a CA key used to sign CRLs, at least for
    the validity period of this certificate. CA's may choose to issue this type
    of certificate with a very short lifetime and renew it frequently. This
    extension is only relevant when the certificate is an authorized OCSP
    responder.

.. class:: AuthorityKeyIdentifier

    .. versionadded:: 0.9

    The authority key identifier extension provides a means of identifying the
    public key corresponding to the private key used to sign a certificate.
    This extension is typically used to assist in determining the appropriate
    certificate chain. For more information about generation and use of this
    extension see `RFC 5280 section 4.2.1.1`_.

    .. attribute:: key_identifier

        :type: bytes

        A value derived from the public key used to verify the certificate's
        signature.

    .. attribute:: authority_cert_issuer

        :type: :class:`Name` or None

        The :class:`Name` of the issuer's issuer.

    .. attribute:: authority_cert_serial_number

        :type: int or None

        The serial number of the issuer's issuer.

.. class:: SubjectKeyIdentifier

    .. versionadded:: 0.9

    The subject key identifier extension provides a means of identifying
    certificates that contain a particular public key.

    .. attribute:: digest

        :type: bytes

        The binary value of the identifier.

.. class:: SubjectAlternativeName

    .. versionadded:: 0.9

    Subject alternative name is an X.509 extension that provides a list of
    :ref:`general name <general_name_classes>` instances that provide a set
    of identities for which the certificate is valid. The object is iterable to
    get every element.

    .. method:: get_values_for_type(type)

        :param type: A :class:`GeneralName` provider. This is one of the
            :ref:`general name classes <general_name_classes>`.

        :returns: A list of values extracted from the matched general names.

        .. doctest::

            >>> from cryptography import x509
            >>> from cryptography.hazmat.backends import default_backend
            >>> from cryptography.hazmat.primitives import hashes
            >>> cert = x509.load_pem_x509_certificate(cryptography_cert_pem, default_backend())
            >>> # Get the subjectAltName extension from the certificate
            >>> ext = cert.extensions.get_extension_for_oid(x509.OID_SUBJECT_ALTERNATIVE_NAME)
            >>> # Get the dNSName entries from the SAN extension
            >>> ext.value.get_values_for_type(x509.DNSName)
            [u'www.cryptography.io', u'cryptography.io']


.. class:: AuthorityInformationAccess

    .. versionadded:: 0.9

    The authority information access extension indicates how to access
    information and services for the issuer of the certificate in which
    the extension appears. Information and services may include online
    validation services (such as OCSP) and issuer data. It is an iterable,
    containing one or more :class:`AccessDescription` instances.


.. class:: AccessDescription

    .. versionadded:: 0.9

    .. attribute:: access_method

        :type: :class:`ObjectIdentifier`

        The access method defines what the ``access_location`` means. It must
        be either :data:`OID_OCSP` or :data:`OID_CA_ISSUERS`. If it is
        :data:`OID_OCSP` the access location will be where to obtain OCSP
        information for the certificate. If it is :data:`OID_CA_ISSUERS` the
        access location will provide additional information about the issuing
        certificate.

    .. attribute:: access_location

        :type: :class:`GeneralName`

        Where to access the information defined by the access method.

.. class:: CRLDistributionPoints

    .. versionadded:: 0.9

    The CRL distribution points extension identifies how CRL information is
    obtained. It is an iterable, containing one or more
    :class:`DistributionPoint` instances.

.. class:: DistributionPoint

    .. versionadded:: 0.9

    .. attribute:: full_name

        :type: list of :class:`GeneralName` instances or None

        This field describes methods to retrieve the CRL. At most one of
        ``full_name`` or ``relative_name`` will be non-None.

    .. attribute:: relative_name

        :type: :class:`Name` or None

        This field describes methods to retrieve the CRL relative to the CRL
        issuer. At most one of ``full_name`` or ``relative_name`` will be
        non-None.

    .. attribute:: crl_issuer

        :type: list of :class:`GeneralName` instances or None

        Information about the issuer of the CRL.

    .. attribute:: reasons

        :type: frozenset of :class:`ReasonFlags` or None

        The reasons a given distribution point may be used for when performing
        revocation checks.

.. class:: ReasonFlags

    .. versionadded:: 0.9

    An enumeration for CRL reasons.

    .. attribute:: unspecified

        It is unspecified why the certificate was revoked. This reason cannot
        be used as a reason flag in a :class:`DistributionPoint`.

    .. attribute:: key_compromise

        This reason indicates that the private key was compromised.

    .. attribute:: ca_compromise

        This reason indicates that the CA issuing the certificate was
        compromised.

    .. attribute:: affiliation_changed

        This reason indicates that the subject's name or other information has
        changed.

    .. attribute:: superseded

        This reason indicates that a certificate has been superseded.

    .. attribute:: cessation_of_operation

        This reason indicates that the certificate is no longer required.

    .. attribute:: certificate_hold

        This reason indicates that the certificate is on hold.

    .. attribute:: privilege_withdrawn

        This reason indicates that the privilege granted by this certificate
        have been withdrawn.

    .. attribute:: aa_compromise

        When an attribute authority has been compromised.

    .. attribute:: remove_from_crl

        This reason indicates that the certificate was on hold and should be
        removed from the CRL. This reason cannot be used as a reason flag
        in a :class:`DistributionPoint`.

.. class:: CertificatePolicies

    .. versionadded:: 0.9

    The certificate policies extension is an iterable, containing one or more
    :class:`PolicyInformation` instances.

Certificate Policies Classes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

These classes may be present within a :class:`CertificatePolicies` instance.

.. class:: PolicyInformation

    .. versionadded:: 0.9

    Contains a policy identifier and an optional list of qualifiers.

    .. attribute:: policy_identifier

        :type: :class:`ObjectIdentifier`

    .. attribute:: policy_qualifiers

        :type: list

        A list consisting of :term:`text` and/or :class:`UserNotice` objects.
        If the value is text it is a pointer to the practice statement
        published by the certificate authority. If it is a user notice it is
        meant for display to the relying party when the certificate is
        used.

.. class:: UserNotice

    .. versionadded:: 0.9

    User notices are intended for display to a relying party when a certificate
    is used. In practice, few if any UIs expose this data and it is a rarely
    encoded component.

    .. attribute:: notice_reference

        :type: :class:`NoticeReference` or None

        The notice reference field names an organization and identifies,
        by number, a particular statement prepared by that organization.

    .. attribute:: explicit_text

        This field includes an arbitrary textual statement directly in the
        certificate.

        :type: :term:`text`

.. class:: NoticeReference

    Notice reference can name an organization and provide information about
    notices related to the certificate. For example, it might identify the
    organization name and notice number 1. Application software could
    have a notice file containing the current set of notices for the named
    organization; the application would then extract the notice text from the
    file and display it. In practice this is rarely seen.

    .. versionadded:: 0.9

    .. attribute:: organization

        :type: :term:`text`

    .. attribute:: notice_numbers

        :type: list

        A list of integers.

Object Identifiers
~~~~~~~~~~~~~~~~~~

X.509 elements are frequently identified by :class:`ObjectIdentifier`
instances. The following common OIDs are available as constants.

Name OIDs
~~~~~~~~~

.. data:: OID_COMMON_NAME

    Corresponds to the dotted string ``"2.5.4.3"``. Historically the domain
    name would be encoded here for server certificates. :rfc:`2818` deprecates
    this practice and names of that type should now be located in a
    SubjectAlternativeName extension. This OID is typically seen in X.509 names.

.. data:: OID_COUNTRY_NAME

    Corresponds to the dotted string ``"2.5.4.6"``. This OID is typically seen
    in X.509 names.

.. data:: OID_LOCALITY_NAME

    Corresponds to the dotted string ``"2.5.4.7"``. This OID is typically seen
    in X.509 names.

.. data:: OID_STATE_OR_PROVINCE_NAME

    Corresponds to the dotted string ``"2.5.4.8"``. This OID is typically seen
    in X.509 names.

.. data:: OID_ORGANIZATION_NAME

    Corresponds to the dotted string ``"2.5.4.10"``. This OID is typically seen
    in X.509 names.

.. data:: OID_ORGANIZATIONAL_UNIT_NAME

    Corresponds to the dotted string ``"2.5.4.11"``. This OID is typically seen
    in X.509 names.

.. data:: OID_SERIAL_NUMBER

    Corresponds to the dotted string ``"2.5.4.5"``. This is distinct from the
    serial number of the certificate itself (which can be obtained with
    :func:`Certificate.serial`). This OID is typically seen in X.509 names.

.. data:: OID_SURNAME

    Corresponds to the dotted string ``"2.5.4.4"``. This OID is typically seen
    in X.509 names.

.. data:: OID_GIVEN_NAME

    Corresponds to the dotted string ``"2.5.4.42"``. This OID is typically seen
    in X.509 names.

.. data:: OID_TITLE

    Corresponds to the dotted string ``"2.5.4.12"``. This OID is typically seen
    in X.509 names.

.. data:: OID_GENERATION_QUALIFIER

    Corresponds to the dotted string ``"2.5.4.44"``. This OID is typically seen
    in X.509 names.

.. data:: OID_DN_QUALIFIER

    Corresponds to the dotted string ``"2.5.4.46"``. This specifies
    disambiguating information to add to the relative distinguished name of an
    entry. See :rfc:`2256`. This OID is typically seen in X.509 names.

.. data:: OID_PSEUDONYM

    Corresponds to the dotted string ``"2.5.4.65"``. This OID is typically seen
    in X.509 names.

.. data:: OID_DOMAIN_COMPONENT

    Corresponds to the dotted string ``"0.9.2342.19200300.100.1.25"``. A string
    holding one component of a domain name. See :rfc:`4519`. This OID is
    typically seen in X.509 names.

.. data:: OID_EMAIL_ADDRESS

    Corresponds to the dotted string ``"1.2.840.113549.1.9.1"``. This OID is
    typically seen in X.509 names.

Signature Algorithm OIDs
~~~~~~~~~~~~~~~~~~~~~~~~

.. data:: OID_RSA_WITH_MD5

    Corresponds to the dotted string ``"1.2.840.113549.1.1.4"``. This is
    an MD5 digest signed by an RSA key.

.. data:: OID_RSA_WITH_SHA1

    Corresponds to the dotted string ``"1.2.840.113549.1.1.5"``. This is
    a SHA1 digest signed by an RSA key.

.. data:: OID_RSA_WITH_SHA224

    Corresponds to the dotted string ``"1.2.840.113549.1.1.14"``. This is
    a SHA224 digest signed by an RSA key.

.. data:: OID_RSA_WITH_SHA256

    Corresponds to the dotted string ``"1.2.840.113549.1.1.11"``. This is
    a SHA256 digest signed by an RSA key.

.. data:: OID_RSA_WITH_SHA384

    Corresponds to the dotted string ``"1.2.840.113549.1.1.12"``. This is
    a SHA384 digest signed by an RSA key.

.. data:: OID_RSA_WITH_SHA512

    Corresponds to the dotted string ``"1.2.840.113549.1.1.13"``. This is
    a SHA512 digest signed by an RSA key.

.. data:: OID_ECDSA_WITH_SHA224

    Corresponds to the dotted string ``"1.2.840.10045.4.3.1"``. This is
    a SHA224 digest signed by an ECDSA key.

.. data:: OID_ECDSA_WITH_SHA256

    Corresponds to the dotted string ``"1.2.840.10045.4.3.2"``. This is
    a SHA256 digest signed by an ECDSA key.

.. data:: OID_ECDSA_WITH_SHA384

    Corresponds to the dotted string ``"1.2.840.10045.4.3.3"``. This is
    a SHA384 digest signed by an ECDSA key.

.. data:: OID_ECDSA_WITH_SHA512

    Corresponds to the dotted string ``"1.2.840.10045.4.3.4"``. This is
    a SHA512 digest signed by an ECDSA key.

.. data:: OID_DSA_WITH_SHA1

    Corresponds to the dotted string ``"1.2.840.10040.4.3"``. This is
    a SHA1 digest signed by a DSA key.

.. data:: OID_DSA_WITH_SHA224

    Corresponds to the dotted string ``"2.16.840.1.101.3.4.3.1"``. This is
    a SHA224 digest signed by a DSA key.

.. data:: OID_DSA_WITH_SHA256

    Corresponds to the dotted string ``"2.16.840.1.101.3.4.3.2"``. This is
    a SHA256 digest signed by a DSA key.

.. _eku_oids:

Extended Key Usage OIDs
~~~~~~~~~~~~~~~~~~~~~~~

.. data:: OID_SERVER_AUTH

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.3.1"``. This is used to
    denote that a certificate may be used for TLS web server authentication.

.. data:: OID_CLIENT_AUTH

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.3.2"``. This is used to
    denote that a certificate may be used for TLS web client authentication.

.. data:: OID_CODE_SIGNING

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.3.3"``. This is used to
    denote that a certificate may be used for code signing.

.. data:: OID_EMAIL_PROTECTION

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.3.4"``. This is used to
    denote that a certificate may be used for email protection.

.. data:: OID_TIME_STAMPING

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.3.8"``. This is used to
    denote that a certificate may be used for time stamping.

.. data:: OID_OCSP_SIGNING

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.3.9"``. This is used to
    denote that a certificate may be used for signing OCSP responses.

Authority Information Access OIDs
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. data:: OID_OCSP

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.48.1"``. Used as the
    identifier for OCSP data in :class:`AccessDescription` objects.

.. data:: OID_CA_ISSUERS

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.48.2"``. Used as the
    identifier for CA issuer data in :class:`AccessDescription` objects.

Policy Qualifier OIDs
~~~~~~~~~~~~~~~~~~~~~

.. data:: OID_CPS_QUALIFIER

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.2.1"``.

.. data:: OID_CPS_USER_NOTICE

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.2.2"``.

.. _extension_oids:

Extension OIDs
~~~~~~~~~~~~~~

.. data:: OID_BASIC_CONSTRAINTS

    Corresponds to the dotted string ``"2.5.29.19"``. The identifier for the
    :class:`BasicConstraints` extension type.

.. data:: OID_KEY_USAGE

    Corresponds to the dotted string ``"2.5.29.15"``. The identifier for the
    :class:`KeyUsage` extension type.

.. data:: OID_SUBJECT_ALTERNATIVE_NAME

    Corresponds to the dotted string ``"2.5.29.17"``. The identifier for the
    :class:`SubjectAlternativeName` extension type.

.. data:: OID_SUBJECT_KEY_IDENTIFIER

    Corresponds to the dotted string ``"2.5.29.14"``. The identifier for the
    :class:`SubjectKeyIdentifier` extension type.

.. data:: OID_CRL_DISTRIBUTION_POINTS

    Corresponds to the dotted string ``"2.5.29.31"``. The identifier for the
    :class:`CRLDistributionPoints` extension type.

.. data:: OID_CERTIFICATE_POLICIES

    Corresponds to the dotted string ``"2.5.29.32"``. The identifier for the
    :class:`CertificatePolicies` extension type.

.. data:: OID_AUTHORITY_KEY_IDENTIFIER

    Corresponds to the dotted string ``"2.5.29.35"``. The identifier for the
    :class:`AuthorityKeyIdentifier` extension type.

.. data:: OID_EXTENDED_KEY_USAGE

    Corresponds to the dotted string ``"2.5.29.37"``. The identifier for the
    :class:`ExtendedKeyUsage` extension type.

.. data:: OID_AUTHORITY_INFORMATION_ACCESS

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.1.1"``. The identifier
    for the :class:`AuthorityInformationAccess` extension type.

.. data:: OID_OCSP_NO_CHECK

    Corresponds to the dotted string ``"1.3.6.1.5.5.7.48.1.5"``. The identifier
    for the :class:`OCSPNoCheck` extension type.

Exceptions
~~~~~~~~~~

.. class:: InvalidVersion

    This is raised when an X.509 certificate has an invalid version number.

    .. attribute:: parsed_version

        :type: int

        Returns the raw version that was parsed from the certificate.

.. class:: DuplicateExtension

    This is raised when more than one X.509 extension of the same type is
    found within a certificate.

    .. attribute:: oid

        :type: :class:`ObjectIdentifier`

        Returns the OID.

.. class:: UnsupportedExtension

    This is raised when a certificate contains an unsupported extension type.

    .. attribute:: oid

        :type: :class:`ObjectIdentifier`

        Returns the OID.

.. class:: ExtensionNotFound

    This is raised when calling :meth:`Extensions.get_extension_for_oid` with
    an extension OID that is not present in the certificate.

    .. attribute:: oid

        :type: :class:`ObjectIdentifier`

        Returns the OID.

.. class:: UnsupportedGeneralNameType

    This is raised when a certificate contains an unsupported general name
    type in an extension.

    .. attribute:: type

        :type: int

        The integer value of the unsupported type. The complete list of
        types can be found in `RFC 5280 section 4.2.1.6`_.


.. _`public key infrastructure`: https://en.wikipedia.org/wiki/Public_key_infrastructure
.. _`TLS`: https://en.wikipedia.org/wiki/Transport_Layer_Security
.. _`RFC 5280 section 4.2.1.1`: https://tools.ietf.org/html/rfc5280#section-4.2.1.1
.. _`RFC 5280 section 4.2.1.6`: https://tools.ietf.org/html/rfc5280#section-4.2.1.6