EVOLUTION-MANAGER

Edit File: reference.rst

X.509 Reference
===============

.. currentmodule:: cryptography.x509

.. testsetup::

pem_crl_data = b"""
    -----BEGIN X509 CRL-----
    MIIBtDCBnQIBAjANBgkqhkiG9w0BAQsFADAnMQswCQYDVQQGEwJVUzEYMBYGA1UE
    AwwPY3J5cHRvZ3JhcGh5LmlvGA8yMDE1MDEwMTAwMDAwMFoYDzIwMTYwMTAxMDAw
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    X4B9vUQNXqc=
    -----END X509 CRL-----
    """.strip()

pem_req_data = b"""
    -----BEGIN CERTIFICATE REQUEST-----
    MIIC0zCCAbsCAQAwWTELMAkGA1UEBhMCVVMxETAPBgNVBAgMCElsbGlub2lzMRAw
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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
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    GVI9+0lAFwxOUnOnwsoI40iOoxjLMGB+CgFLKCGUcWxP
    -----END CERTIFICATE-----
    """.strip()

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`.

.. doctest::

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

.. 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`.

Loading Certificate Revocation Lists
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. function:: load_pem_x509_crl(data, backend)

.. versionadded:: 1.1

Deserialize a certificate revocation list (CRL) from PEM encoded data. PEM
    requests are base64 decoded and have delimiters that look like
    ``-----BEGIN X509 CRL-----``.

: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.CertificateRevocationList`.

.. doctest::

>>> from cryptography import x509
        >>> from cryptography.hazmat.backends import default_backend
        >>> from cryptography.hazmat.primitives import hashes
        >>> crl = x509.load_pem_x509_crl(pem_crl_data, default_backend())
        >>> isinstance(crl.signature_hash_algorithm, hashes.SHA256)
        True

.. function:: load_der_x509_crl(data, backend)

.. versionadded:: 1.1

Deserialize a certificate revocation list (CRL) from DER encoded data. DER
    is a binary format.

: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.CertificateRevocationList`.

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`.

.. 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

.. 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`.

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_number

:type: int

The serial as a Python integer.

.. doctest::

>>> cert.serial_number
            2

.. method:: public_key()

The public key associated with the certificate.

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

.. 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:: signature_algorithm_oid

.. versionadded:: 1.6

:type: :class:`ObjectIdentifier`

Returns the :class:`ObjectIdentifier` of the signature algorithm used
        to sign the certificate. This will be one of the OIDs from
        :class:`~cryptography.x509.oid.SignatureAlgorithmOID`.

.. doctest::

>>> cert.signature_algorithm_oid
            <ObjectIdentifier(oid=1.2.840.113549.1.1.11, name=sha256WithRSAEncryption)>

.. 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.

:raises UnicodeError: If an extension contains IDNA encoding that is
            invalid or not compliant with IDNA 2008.

.. 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)>)>

.. attribute:: signature

.. versionadded:: 1.2

:type: bytes

The bytes of the certificate's signature.

.. attribute:: tbs_certificate_bytes

.. versionadded:: 1.2

:type: bytes

The DER encoded bytes payload (as defined by :rfc:`5280`) that is hashed
        and then signed by the private key of the certificate's issuer. This
        data may be used to validate a signature, but use extreme caution as
        certificate validation is a complex problem that involves much more
        than just signature checks.

.. method:: public_bytes(encoding)

.. versionadded:: 1.0

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

:return bytes: The data that can be written to a file or sent
            over the network to be verified by clients.

X.509 CRL (Certificate Revocation List) Object
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. class:: CertificateRevocationList

.. versionadded:: 1.0

A CertificateRevocationList is an object representing a list of revoked
    certificates. The object is iterable and will yield the RevokedCertificate
    objects stored in this CRL.

.. doctest::

>>> len(crl)
            1
            >>> revoked_certificate = crl[0]
            >>> type(revoked_certificate)
            <class 'cryptography.hazmat.backends.openssl.x509._RevokedCertificate'>
            >>> for r in crl:
            ...     print(r.serial_number)
            0

.. 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
            >>> crl.fingerprint(hashes.SHA256())
            'e\xcf.\xc4:\x83?1\xdc\xf3\xfc\x95\xd7\xb3\x87\xb3\x8e\xf8\xb93!\x87\x07\x9d\x1b\xb4!\xb9\xe4W\xf4\x1f'

.. 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 CRL.

.. doctest::

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

.. attribute:: signature_algorithm_oid

.. versionadded:: 1.6

:type: :class:`ObjectIdentifier`

Returns the :class:`ObjectIdentifier` of the signature algorithm used
        to sign the CRL. This will be one of the OIDs from
        :class:`~cryptography.x509.oid.SignatureAlgorithmOID`.

.. doctest::

>>> crl.signature_algorithm_oid
            <ObjectIdentifier(oid=1.2.840.113549.1.1.11, name=sha256WithRSAEncryption)>

.. attribute:: issuer

:type: :class:`Name`

The :class:`Name` of the issuer.

.. doctest::

>>> crl.issuer
            <Name([<NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.6, name=countryName)>, value=u'US')>, <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.3, name=commonName)>, value=u'cryptography.io')>])>

.. attribute:: next_update

:type: :class:`datetime.datetime`

A naïve datetime representing when the next update to this CRL is
        expected.

.. doctest::

>>> crl.next_update
            datetime.datetime(2016, 1, 1, 0, 0)

.. attribute:: last_update

:type: :class:`datetime.datetime`

A naïve datetime representing when the this CRL was last updated.

.. doctest::

>>> crl.last_update
            datetime.datetime(2015, 1, 1, 0, 0)

.. attribute:: extensions

:type: :class:`Extensions`

The extensions encoded in the CRL.

.. attribute:: signature

.. versionadded:: 1.2

:type: bytes

The bytes of the CRL's signature.

.. attribute:: tbs_certlist_bytes

.. versionadded:: 1.2

:type: bytes

The DER encoded bytes payload (as defined by :rfc:`5280`) that is hashed
        and then signed by the private key of the CRL's issuer. This data may be
        used to validate a signature, but use extreme caution as CRL validation
        is a complex problem that involves much more than just signature checks.

.. method:: public_bytes(encoding)

.. versionadded:: 1.2

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

:return bytes: The data that can be written to a file or sent
            over the network and used as part of a certificate verification
            process.

X.509 Certificate Builder
~~~~~~~~~~~~~~~~~~~~~~~~~

.. class:: CertificateBuilder

.. versionadded:: 1.0

.. doctest::

>>> from cryptography import x509
        >>> from cryptography.hazmat.backends import default_backend
        >>> from cryptography.hazmat.primitives import hashes
        >>> from cryptography.hazmat.primitives.asymmetric import rsa
        >>> from cryptography.x509.oid import NameOID
        >>> import datetime
        >>> one_day = datetime.timedelta(1, 0, 0)
        >>> private_key = rsa.generate_private_key(
        ...     public_exponent=65537,
        ...     key_size=2048,
        ...     backend=default_backend()
        ... )
        >>> public_key = private_key.public_key()
        >>> builder = x509.CertificateBuilder()
        >>> builder = builder.subject_name(x509.Name([
        ...     x509.NameAttribute(NameOID.COMMON_NAME, u'cryptography.io'),
        ... ]))
        >>> builder = builder.issuer_name(x509.Name([
        ...     x509.NameAttribute(NameOID.COMMON_NAME, u'cryptography.io'),
        ... ]))
        >>> builder = builder.not_valid_before(datetime.datetime.today() - one_day)
        >>> builder = builder.not_valid_after(datetime.datetime(2018, 8, 2))
        >>> builder = builder.serial_number(x509.random_serial_number())
        >>> builder = builder.public_key(public_key)
        >>> builder = builder.add_extension(
        ...     x509.BasicConstraints(ca=False, path_length=None), critical=True,
        ... )
        >>> certificate = builder.sign(
        ...     private_key=private_key, algorithm=hashes.SHA256(),
        ...     backend=default_backend()
        ... )
        >>> isinstance(certificate, x509.Certificate)
        True

.. method:: issuer_name(name)

Sets the issuer's distinguished name.

:param name: The :class:`~cryptography.x509.Name` that describes the
            issuer (CA).

.. method:: subject_name(name)

Sets the subject's distinguished name.

:param name: The :class:`~cryptography.x509.Name` that describes the
            subject.

.. method:: public_key(public_key)

Sets the subject's public key.

:param public_key: The subject's public key. This can be one of
            :class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKey`,
            :class:`~cryptography.hazmat.primitives.asymmetric.dsa.DSAPublicKey` or
            :class:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey`

.. method:: serial_number(serial_number)

Sets the certificate's serial number (an integer).  The CA's policy
        determines how it attributes serial numbers to certificates. This
        number must uniquely identify the certificate given the issuer.
        `CABForum Guidelines`_ require entropy in the serial number
        to provide protection against hash collision attacks. For more
        information on secure random number generation, see
        :doc:`/random-numbers`.

:param serial_number: Integer number that will be used by the CA to
            identify this certificate (most notably during certificate
            revocation checking). Users should consider using
            :func:`~cryptography.x509.random_serial_number` when possible.

.. method:: not_valid_before(time)

Sets the certificate's activation time.  This is the time from which
        clients can start trusting the certificate.  It may be different from
        the time at which the certificate was created.

:param time: The :class:`datetime.datetime` object (in UTC) that marks the
            activation time for the certificate.  The certificate may not be
            trusted clients if it is used before this time.

.. method:: not_valid_after(time)

Sets the certificate's expiration time.  This is the time from which
        clients should no longer trust the certificate.  The CA's policy will
        determine how long the certificate should remain in use.

:param time: The :class:`datetime.datetime` object (in UTC) that marks the
            expiration time for the certificate.  The certificate may not be
            trusted clients if it is used after this time.

.. method:: add_extension(extension, critical)

Adds an X.509 extension to the certificate.

:param extension: An extension conforming to the
            :class:`~cryptography.x509.ExtensionType` interface.

:param critical: Set to ``True`` if the extension must be understood and
             handled by whoever reads the certificate.

.. method:: sign(private_key, algorithm, backend)

Sign the certificate using the CA's private key.

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

:param backend: Backend that will be used to build the certificate.
            Must support the
            :class:`~cryptography.hazmat.backends.interfaces.X509Backend`
            interface.

:returns: :class:`~cryptography.x509.Certificate`

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

.. class:: CertificateSigningRequest

.. versionadded:: 0.9

.. method:: public_key()

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

.. attribute:: signature_algorithm_oid

.. versionadded:: 1.6

:type: :class:`ObjectIdentifier`

Returns the :class:`ObjectIdentifier` of the signature algorithm used
        to sign the request. This will be one of the OIDs from
        :class:`~cryptography.x509.oid.SignatureAlgorithmOID`.

.. doctest::

>>> csr.signature_algorithm_oid
            <ObjectIdentifier(oid=1.2.840.113549.1.1.5, name=sha1WithRSAEncryption)>

.. attribute:: extensions

:type: :class:`Extensions`

The extensions encoded in the certificate signing request.

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

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

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

:raises UnicodeError: If an extension contains IDNA encoding that is
            invalid or not compliant with IDNA 2008.

.. method:: public_bytes(encoding)

.. versionadded:: 1.0

: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.

.. attribute:: signature

.. versionadded:: 1.2

:type: bytes

The bytes of the certificate signing request's signature.

.. attribute:: tbs_certrequest_bytes

.. versionadded:: 1.2

:type: bytes

The DER encoded bytes payload (as defined by :rfc:`2986`) that is
        hashed and then signed by the private key (corresponding to the public
        key embedded in the CSR). This data may be used to validate the CSR
        signature.

.. attribute:: is_signature_valid

.. versionadded:: 1.3

Returns True if the CSR signature is correct, False otherwise.

X.509 Certificate Revocation List Builder
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. class:: CertificateRevocationListBuilder

.. versionadded:: 1.2

.. doctest::

>>> from cryptography import x509
        >>> from cryptography.hazmat.backends import default_backend
        >>> from cryptography.hazmat.primitives import hashes
        >>> from cryptography.hazmat.primitives.asymmetric import rsa
        >>> from cryptography.x509.oid import NameOID
        >>> import datetime
        >>> one_day = datetime.timedelta(1, 0, 0)
        >>> private_key = rsa.generate_private_key(
        ...     public_exponent=65537,
        ...     key_size=2048,
        ...     backend=default_backend()
        ... )
        >>> builder = x509.CertificateRevocationListBuilder()
        >>> builder = builder.issuer_name(x509.Name([
        ...     x509.NameAttribute(NameOID.COMMON_NAME, u'cryptography.io CA'),
        ... ]))
        >>> builder = builder.last_update(datetime.datetime.today())
        >>> builder = builder.next_update(datetime.datetime.today() + one_day)
        >>> revoked_cert = x509.RevokedCertificateBuilder().serial_number(
        ...     333
        ... ).revocation_date(
        ...     datetime.datetime.today()
        ... ).build(default_backend())
        >>> builder = builder.add_revoked_certificate(revoked_cert)
        >>> crl = builder.sign(
        ...     private_key=private_key, algorithm=hashes.SHA256(),
        ...     backend=default_backend()
        ... )
        >>> len(crl)
        1

.. method:: issuer_name(name)

Sets the issuer's distinguished name.

:param name: The :class:`~cryptography.x509.Name` that describes the
            issuer (CA).

.. method:: last_update(time)

Sets this CRL's activation time.  This is the time from which
        clients can start trusting this CRL.  It may be different from
        the time at which this CRL was created. This is also known as the
        ``thisUpdate`` time.

:param time: The :class:`datetime.datetime` object (in UTC) that marks
            the activation time for this CRL.  The CRL may not be trusted if it
            is used before this time.

.. method:: next_update(time)

Sets this CRL's next update time. This is the time by which
        a new CRL will be issued. The CA is allowed to issue a new CRL before
        this date, however clients are not required to check for it.

:param time: The :class:`datetime.datetime` object (in UTC) that marks
            the next update time for this CRL.

.. method:: add_extension(extension, critical)

Adds an X.509 extension to this CRL.

:param extension: An extension with the
            :class:`~cryptography.x509.ExtensionType` interface.

:param critical: Set to ``True`` if the extension must be understood and
             handled by whoever reads the CRL.

.. method:: add_revoked_certificate(revoked_certificate)

Adds a revoked certificate to this CRL.

:param revoked_certificate: An instance of
            :class:`~cryptography.x509.RevokedCertificate`. These can be
            obtained from an existing CRL or created with
            :class:`~cryptography.x509.RevokedCertificateBuilder`.

.. method:: sign(private_key, algorithm, backend)

Sign this CRL using the CA's private key.

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

:param backend: Backend that will be used to build the CRL.
            Must support the
            :class:`~cryptography.hazmat.backends.interfaces.X509Backend`
            interface.

:returns: :class:`~cryptography.x509.CertificateRevocationList`

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

.. class:: RevokedCertificate

.. versionadded:: 1.0

.. attribute:: serial_number

:type: :class:`int`

An integer representing the serial number of the revoked certificate.

.. doctest::

>>> revoked_certificate.serial_number
            0

.. attribute:: revocation_date

:type: :class:`datetime.datetime`

A naïve datetime representing the date this certificates was revoked.

.. doctest::

>>> revoked_certificate.revocation_date
            datetime.datetime(2015, 1, 1, 0, 0)

.. attribute:: extensions

:type: :class:`Extensions`

The extensions encoded in the revoked certificate.

.. doctest::

>>> for ext in revoked_certificate.extensions:
            ...     print(ext)
            <Extension(oid=<ObjectIdentifier(oid=2.5.29.24, name=invalidityDate)>, critical=False, value=<InvalidityDate(invalidity_date=2015-01-01 00:00:00)>)>
            <Extension(oid=<ObjectIdentifier(oid=2.5.29.21, name=cRLReason)>, critical=False, value=<CRLReason(reason=ReasonFlags.key_compromise)>)>

X.509 Revoked Certificate Builder
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. class:: RevokedCertificateBuilder

This class is used to create :class:`~cryptography.x509.RevokedCertificate`
    objects that can be used with the
    :class:`~cryptography.x509.CertificateRevocationListBuilder`.

.. versionadded:: 1.2

.. doctest::

>>> from cryptography import x509
        >>> from cryptography.hazmat.backends import default_backend
        >>> import datetime
        >>> builder = x509.RevokedCertificateBuilder()
        >>> builder = builder.revocation_date(datetime.datetime.today())
        >>> builder = builder.serial_number(3333)
        >>> revoked_certificate = builder.build(default_backend())
        >>> isinstance(revoked_certificate, x509.RevokedCertificate)
        True

.. method:: serial_number(serial_number)

Sets the revoked certificate's serial number.

:param serial_number: Integer number that is used to identify the
            revoked certificate.

.. method:: revocation_date(time)

Sets the certificate's revocation date.

:param time: The :class:`datetime.datetime` object (in UTC) that marks the
            revocation time for the certificate.

.. method:: add_extension(extension, critical)

Adds an X.509 extension to this revoked certificate.

:param extension: An instance of one of the
            :ref:`CRL entry extensions <crl_entry_extensions>`.

:param critical: Set to ``True`` if the extension must be understood and
             handled.

.. method:: build(backend)

Create a revoked certificate object using the provided backend.

:param backend: Backend that will be used to build the revoked
            certificate.  Must support the
            :class:`~cryptography.hazmat.backends.interfaces.X509Backend`
            interface.

:returns: :class:`~cryptography.x509.RevokedCertificate`

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

.. class:: CertificateSigningRequestBuilder

.. versionadded:: 1.0

.. doctest::

.. method:: subject_name(name)

:param name: The :class:`~cryptography.x509.Name` of the certificate
            subject.
        :returns: A new
            :class:`~cryptography.x509.CertificateSigningRequestBuilder`.

.. method:: add_extension(extension, critical)

:param extension: An extension conforming to the
            :class:`~cryptography.x509.ExtensionType` interface.
        :param critical: Set to `True` if the extension must be understood and
             handled by whoever reads the certificate.
        :returns: A new
            :class:`~cryptography.x509.CertificateSigningRequestBuilder`.

.. method:: sign(private_key, algorithm, backend)

:param backend: Backend that will be used to sign the request.
            Must support the
            :class:`~cryptography.hazmat.backends.interfaces.X509Backend`
            interface.

:param private_key: The
            :class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKey`,
            :class:`~cryptography.hazmat.primitives.asymmetric.dsa.DSAPrivateKey` or
            :class:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKey`
            that will be used to sign the request.  When the request is
            signed by a certificate authority, the private key's associated
            public key will be stored in the resulting certificate.

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

:returns: A new
            :class:`~cryptography.x509.CertificateSigningRequest`.

.. 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``).

Technically, a Name is a list of *sets* of attributes, called *Relative
    Distinguished Names* or *RDNs*, although multi-valued RDNs are rarely
    encountered.  The iteration order of values within a multi-valued RDN is
    undefined.  If you need to handle multi-valued RDNs, the ``rdns`` property
    gives access to an ordered list of :class:`RelativeDistinguishedName`
    objects.

A Name can be initialized with an iterable of :class:`NameAttribute` (the
    common case where each RDN has a single attribute) or an iterable of
    :class:`RelativeDistinguishedName` objects (in the rare case of
    multi-valued RDNs).

.. 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')>

.. attribute:: rdns

.. versionadded:: 1.6

:type: list of :class:`RelativeDistinguishedName`

.. 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(NameOID.COMMON_NAME)
            [<NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.3, name=commonName)>, value=u'Good CA')>]

.. method:: public_bytes(backend)

.. versionadded:: 1.6

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

:return bytes: The DER encoded name.

.. 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 :class:`RelativeDistinguishedName`
    instances, which consist of a set of :class:`NameAttribute` instances.

.. attribute:: oid

:type: :class:`ObjectIdentifier`

The attribute OID.

.. attribute:: value

:type: :term:`text`

The value of the attribute.

.. class:: RelativeDistinguishedName(attributes)

.. versionadded:: 1.6

A relative distinguished name is a non-empty set of name attributes.  The
    object is iterable to get every attribute.

.. method:: get_attributes_for_oid(oid)

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

:returns: A list of :class:`NameAttribute` instances that match the OID
            provided.  The list should contain zero or one values.

.. 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(value)

.. versionadded:: 0.9

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

.. attribute:: value

:type: :term:`text`

.. class:: DNSName(value)

.. versionadded:: 0.9

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

.. attribute:: value

:type: :term:`text`

.. class:: DirectoryName(value)

.. versionadded:: 0.9

This corresponds to a directory name.

.. attribute:: value

:type: :class:`Name`

.. class:: UniformResourceIdentifier(value)

.. 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(value)

.. 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(value)

.. versionadded:: 0.9

This corresponds to a registered ID.

.. attribute:: value

:type: :class:`ObjectIdentifier`

.. class:: OtherName(type_id, value)

.. versionadded:: 1.0

This corresponds to an ``otherName.``  An ``otherName`` has a type identifier and a value represented in binary DER format.

.. attribute:: type_id

:type: :class:`ObjectIdentifier`

.. attribute:: value

:type: `bytes`

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::

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

.. method:: get_extension_for_class(extclass)

.. versionadded:: 1.1

:param extclass: An extension class.

:returns: An instance of the extension class.

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

.. doctest::

>>> from cryptography import x509
            >>> cert.extensions.get_extension_for_class(x509.BasicConstraints)
            <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`

One of the :class:`~cryptography.x509.oid.ExtensionOID` 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:: ExtensionType

.. versionadded:: 1.0

This is the interface against which all the following extension types are
    registered.

.. class:: KeyUsage(digital_signature, content_commitment, key_encipherment, data_encipherment, key_agreement, key_cert_sign, crl_sign, encipher_only, decipher_only)

.. 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.

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns :attr:`~cryptography.x509.oid.ExtensionOID.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(ca, path_length)

.. 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.

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns :attr:`~cryptography.x509.oid.ExtensionOID.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(usages)

.. 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
    :class:`~cryptography.x509.oid.ExtendedKeyUsageOID` OIDs present.

:param list usages: A list of
        :class:`~cryptography.x509.oid.ExtendedKeyUsageOID` OIDs.

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns :attr:`~cryptography.x509.oid.ExtensionOID.EXTENDED_KEY_USAGE`.

.. class:: OCSPNoCheck()

.. versionadded:: 1.0

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.

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns :attr:`~cryptography.x509.oid.ExtensionOID.OCSP_NO_CHECK`.

.. class:: NameConstraints(permitted_subtrees, excluded_subtrees)

.. versionadded:: 1.0

The name constraints extension, which only has meaning in a CA certificate,
    defines a name space within which all subject names in certificates issued
    beneath the CA certificate must (or must not) be in. For specific details
    on the way this extension should be processed see :rfc:`5280`.

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns :attr:`~cryptography.x509.oid.ExtensionOID.NAME_CONSTRAINTS`.

.. attribute:: permitted_subtrees

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

The set of permitted name patterns. If a name matches this and an
        element in ``excluded_subtrees`` it is invalid. At least one of
        ``permitted_subtrees`` and ``excluded_subtrees`` will be non-None.

.. attribute:: excluded_subtrees

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

Any name matching a restriction in the ``excluded_subtrees`` field is
        invalid regardless of information appearing in the
        ``permitted_subtrees``. At least one of ``permitted_subtrees`` and
        ``excluded_subtrees`` will be non-None.

.. class:: AuthorityKeyIdentifier(key_identifier, authority_cert_issuer, authority_cert_serial_number)

.. 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:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.ExtensionOID.AUTHORITY_KEY_IDENTIFIER`.

.. 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.

.. classmethod:: from_issuer_public_key(public_key)

.. versionadded:: 1.0

.. note::

This method should be used if the issuer certificate does not
            contain a :class:`~cryptography.x509.SubjectKeyIdentifier`.
            Otherwise, use
            :meth:`~cryptography.x509.AuthorityKeyIdentifier.from_issuer_subject_key_identifier`.

Creates a new AuthorityKeyIdentifier instance using the public key
        provided to generate the appropriate digest. This should be the
        **issuer's public key**. The resulting object will contain
        :attr:`~cryptography.x509.AuthorityKeyIdentifier.key_identifier`, but
        :attr:`~cryptography.x509.AuthorityKeyIdentifier.authority_cert_issuer`
        and
        :attr:`~cryptography.x509.AuthorityKeyIdentifier.authority_cert_serial_number`
        will be None.
        The generated ``key_identifier`` is the SHA1 hash of the ``subjectPublicKey``
        ASN.1 bit string. This is the first recommendation in :rfc:`5280`
        section 4.2.1.2.

:param public_key: One of
            :class:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKey`
            ,
            :class:`~cryptography.hazmat.primitives.asymmetric.dsa.DSAPublicKey`
            , or
            :class:`~cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey`.

.. doctest::

>>> from cryptography import x509
            >>> from cryptography.hazmat.backends import default_backend
            >>> issuer_cert = x509.load_pem_x509_certificate(pem_data, default_backend())
            >>> x509.AuthorityKeyIdentifier.from_issuer_public_key(issuer_cert.public_key())
            <AuthorityKeyIdentifier(key_identifier='X\x01\x84$\x1b\xbc+R\x94J=\xa5\x10r\x14Q\xf5\xaf:\xc9', authority_cert_issuer=None, authority_cert_serial_number=None)>

.. classmethod:: from_issuer_subject_key_identifier(ski)

.. versionadded:: 1.3

.. note::
            This method should be used if the issuer certificate contains a
            :class:`~cryptography.x509.SubjectKeyIdentifier`.  Otherwise, use
            :meth:`~cryptography.x509.AuthorityKeyIdentifier.from_issuer_public_key`.

Creates a new AuthorityKeyIdentifier instance using the
        SubjectKeyIdentifier from the issuer certificate. The resulting object
        will contain
        :attr:`~cryptography.x509.AuthorityKeyIdentifier.key_identifier`, but
        :attr:`~cryptography.x509.AuthorityKeyIdentifier.authority_cert_issuer`
        and
        :attr:`~cryptography.x509.AuthorityKeyIdentifier.authority_cert_serial_number`
        will be None.

:param ski: The
            :class:`~cryptography.x509.SubjectKeyIdentifier` from the issuer
            certificate.

.. doctest::

>>> from cryptography import x509
            >>> from cryptography.hazmat.backends import default_backend
            >>> issuer_cert = x509.load_pem_x509_certificate(pem_data, default_backend())
            >>> ski = issuer_cert.extensions.get_extension_for_class(x509.SubjectKeyIdentifier)
            >>> x509.AuthorityKeyIdentifier.from_issuer_subject_key_identifier(ski)
            <AuthorityKeyIdentifier(key_identifier='X\x01\x84$\x1b\xbc+R\x94J=\xa5\x10r\x14Q\xf5\xaf:\xc9', authority_cert_issuer=None, authority_cert_serial_number=None)>

.. class:: SubjectKeyIdentifier(digest)

.. versionadded:: 0.9

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

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.ExtensionOID.SUBJECT_KEY_IDENTIFIER`.

.. attribute:: digest

:type: bytes

The binary value of the identifier.

.. classmethod:: from_public_key(public_key)

.. versionadded:: 1.0

Creates a new SubjectKeyIdentifier instance using the public key
        provided to generate the appropriate digest. This should be the public
        key that is in the certificate. The generated digest is the SHA1 hash
        of the ``subjectPublicKey`` ASN.1 bit string. This is the first
        recommendation in :rfc:`5280` section 4.2.1.2.

.. doctest::

>>> from cryptography import x509
            >>> from cryptography.hazmat.backends import default_backend
            >>> csr = x509.load_pem_x509_csr(pem_req_data, default_backend())
            >>> x509.SubjectKeyIdentifier.from_public_key(csr.public_key())
            <SubjectKeyIdentifier(digest='\xdb\xaa\xf0\x06\x11\xdbD\xfe\xbf\x93\x03\x8av\x88WP7\xa6\x91\xf7')>

.. class:: SubjectAlternativeName(general_names)

.. 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.

:param list general_names: A list of :class:`GeneralName` instances.

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.ExtensionOID.SUBJECT_ALTERNATIVE_NAME`.

.. method:: get_values_for_type(type)

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

:returns: A list of values extracted from the matched general names.
            The type of the returned values depends on the :class:`GeneralName`.

.. 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(ExtensionOID.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:: IssuerAlternativeName(general_names)

.. versionadded:: 1.0

Issuer 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 the certificate issuer. The object is iterable to
    get every element.

:param list general_names: A list of :class:`GeneralName` instances.

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.ExtensionOID.ISSUER_ALTERNATIVE_NAME`.

.. method:: get_values_for_type(type)

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

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

.. class:: AuthorityInformationAccess(descriptions)

.. 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:`~cryptography.x509.AccessDescription`
    instances.

:param list descriptions: A list of :class:`AccessDescription` objects.

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.ExtensionOID.AUTHORITY_INFORMATION_ACCESS`.

.. class:: AccessDescription(access_method, access_location)

.. versionadded:: 0.9

.. attribute:: access_method

:type: :class:`ObjectIdentifier`

The access method defines what the ``access_location`` means. It must
        be either
        :attr:`~cryptography.x509.oid.AuthorityInformationAccessOID.OCSP` or
        :attr:`~cryptography.x509.oid.AuthorityInformationAccessOID.CA_ISSUERS`.
        If it is
        :attr:`~cryptography.x509.oid.AuthorityInformationAccessOID.OCSP`
        the access location will be where to obtain OCSP
        information for the certificate. If it is
        :attr:`~cryptography.x509.oid.AuthorityInformationAccessOID.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(distribution_points)

.. 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.

:param list distribution_points: A list of :class:`DistributionPoint`
        instances.

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.ExtensionOID.CRL_DISTRIBUTION_POINTS`.

.. class:: DistributionPoint(full_name, relative_name, reasons, crl_issuer)

.. 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:`RelativeDistinguishedName` 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.

.. versionchanged:: 1.6
            Changed from :class:`Name` to :class:`RelativeDistinguishedName`.

.. 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:: InhibitAnyPolicy(skip_certs)

.. versionadded:: 1.0

The inhibit ``anyPolicy`` extension indicates that the special OID
    :attr:`~cryptography.x509.oid.CertificatePoliciesOID.ANY_POLICY`, is not
    considered an explicit match for other :class:`CertificatePolicies` except
    when it appears in an intermediate self-issued CA certificate.  The value
    indicates the number of additional non-self-issued certificates that may
    appear in the path before
    :attr:`~cryptography.x509.oid.CertificatePoliciesOID.ANY_POLICY` is no
    longer permitted.  For example, a value of one indicates that
    :attr:`~cryptography.x509.oid.CertificatePoliciesOID.ANY_POLICY` may be
    processed in certificates issued by the subject of this certificate, but
    not in additional certificates in the path.

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.ExtensionOID.INHIBIT_ANY_POLICY`.

.. attribute:: skip_certs

:type: int

.. class:: PolicyConstraints

.. versionadded:: 1.3

The policy constraints extension is used to inhibit policy mapping or
    require that each certificate in a chain contain an acceptable policy
    identifier. For more information about the use of this extension see
    :rfc:`5280`.

.. attribute:: oid

:type: :class:`ObjectIdentifier`

Returns :attr:`~cryptography.x509.oid.ExtensionOID.POLICY_CONSTRAINTS`.

.. attribute:: require_explicit_policy

:type: int or None

If this field is not None, the value indicates the number of additional
        certificates that may appear in the chain before an explicit policy is
        required for the entire path. When an explicit policy is required, it
        is necessary for all certificates in the chain to contain an acceptable
        policy identifier in the certificate policies extension.  An
        acceptable policy identifier is the identifier of a policy required
        by the user of the certification path or the identifier of a policy
        that has been declared equivalent through policy mapping.

.. attribute:: inhibit_policy_mapping

:type: int or None

If this field is not None, the value indicates the number of additional
        certificates that may appear in the chain before policy mapping is no
        longer permitted.  For example, a value of one indicates that policy
        mapping may be processed in certificates issued by the subject of this
        certificate, but not in additional certificates in the chain.

.. class:: CRLNumber(crl_number)

.. versionadded:: 1.2

The CRL number is a CRL extension that conveys a monotonically increasing
    sequence number for a given CRL scope and CRL issuer. This extension allows
    users to easily determine when a particular CRL supersedes another CRL.
    :rfc:`5280` requires that this extension be present in conforming CRLs.

.. attribute:: oid

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.ExtensionOID.CRL_NUMBER`.

.. attribute:: crl_number

:type: int

.. class:: UnrecognizedExtension

.. versionadded:: 1.2

A generic extension class used to hold the raw value of **non-critical**
    extensions that ``cryptography`` does not know how to parse. Extensions
    marked critical will raise
    :class:`~cryptography.x509.UnsupportedExtension`.

.. attribute:: oid

:type: :class:`ObjectIdentifier`

Returns the OID associated with this extension.

.. attribute:: value

:type: byte

Returns the DER encoded bytes payload of the extension.

.. class:: CertificatePolicies(policies)

.. versionadded:: 0.9

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

:param list policies: A list of :class:`PolicyInformation` instances.

.. attribute:: oid

.. versionadded:: 1.0

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.ExtensionOID.CERTIFICATE_POLICIES`.

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

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

.. class:: PolicyInformation(policy_identifier, policy_qualifiers)

.. 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(notice_reference, explicit_text)

.. 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(organization, notice_numbers)

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.

.. _crl_entry_extensions:

CRL Entry Extensions
~~~~~~~~~~~~~~~~~~~~

These extensions are only valid within a :class:`RevokedCertificate` object.

.. class:: CertificateIssuer(general_names)

.. versionadded:: 1.2

The certificate issuer is an extension that is only valid inside
    :class:`~cryptography.x509.RevokedCertificate` objects.  If the
    ``indirectCRL`` property of the parent CRL's IssuingDistributionPoint
    extension is set, then this extension identifies the certificate issuer
    associated with the revoked certificate. The object is iterable to get
    every element.

:param list general_names: A list of :class:`GeneralName` instances.

.. attribute:: oid

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.CRLEntryExtensionOID.CERTIFICATE_ISSUER`.

.. method:: get_values_for_type(type)

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

:returns: A list of values extracted from the matched general names.
            The type of the returned values depends on the :class:`GeneralName`.

.. class:: CRLReason(reason)

.. versionadded:: 1.2

CRL reason (also known as ``reasonCode``) is an extension that is only
    valid inside :class:`~cryptography.x509.RevokedCertificate` objects. It
    identifies a reason for the certificate revocation.

:param reason: A value from the
        :class:`~cryptography.x509.oid.CRLEntryExtensionOID` enum.

.. attribute:: oid

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.CRLEntryExtensionOID.CRL_REASON`.

.. attribute:: reason

:type: An element from :class:`~cryptography.x509.ReasonFlags`

.. class:: InvalidityDate(invalidity_date)

.. versionadded:: 1.2

Invalidity date is an extension that is only valid inside
    :class:`~cryptography.x509.RevokedCertificate` objects. It provides
    the date on which it is known or suspected that the private key was
    compromised or that the certificate otherwise became invalid.
    This date may be earlier than the revocation date in the CRL entry,
    which is the date at which the CA processed the revocation.

:param invalidity_date: The :class:`datetime.datetime` when it is known
        or suspected that the private key was compromised.

.. attribute:: oid

:type: :class:`ObjectIdentifier`

Returns
        :attr:`~cryptography.x509.oid.CRLEntryExtensionOID.INVALIDITY_DATE`.

.. attribute:: invalidity_date

:type: :class:`datetime.datetime`

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

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

.. currentmodule:: cryptography.x509.oid

.. class:: NameOID

These OIDs are typically seen in X.509 names.

.. versionadded:: 1.0

.. attribute:: 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 :class:`~cryptography.x509.SubjectAlternativeName` extension.

.. attribute:: COUNTRY_NAME

Corresponds to the dotted string ``"2.5.4.6"``.

.. attribute:: LOCALITY_NAME

Corresponds to the dotted string ``"2.5.4.7"``.

.. attribute:: STATE_OR_PROVINCE_NAME

Corresponds to the dotted string ``"2.5.4.8"``.

.. attribute:: STREET_ADDRESS

.. versionadded:: 1.6

Corresponds to the dotted string ``"2.5.4.9"``.

.. attribute:: ORGANIZATION_NAME

Corresponds to the dotted string ``"2.5.4.10"``.

.. attribute:: ORGANIZATIONAL_UNIT_NAME

Corresponds to the dotted string ``"2.5.4.11"``.

.. attribute:: 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:`~cryptography.x509.Certificate.serial_number`).

.. attribute:: SURNAME

Corresponds to the dotted string ``"2.5.4.4"``.

.. attribute:: GIVEN_NAME

Corresponds to the dotted string ``"2.5.4.42"``.

.. attribute:: TITLE

Corresponds to the dotted string ``"2.5.4.12"``.

.. attribute:: GENERATION_QUALIFIER

Corresponds to the dotted string ``"2.5.4.44"``.

.. attribute:: X500_UNIQUE_IDENTIFIER

.. versionadded:: 1.6

Corresponds to the dotted string ``"2.5.4.45"``.

.. attribute:: 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`.

.. attribute:: PSEUDONYM

Corresponds to the dotted string ``"2.5.4.65"``.

.. attribute:: USER_ID

.. versionadded:: 1.6

Corresponds to the dotted string ``"0.9.2342.19200300.100.1.1"``.

.. attribute:: 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`.

.. attribute:: EMAIL_ADDRESS

Corresponds to the dotted string ``"1.2.840.113549.1.9.1"``.

.. attribute:: JURISDICTION_COUNTRY_NAME

Corresponds to the dotted string ``"1.3.6.1.4.1.311.60.2.1.3"``.

.. attribute:: JURISDICTION_LOCALITY_NAME

Corresponds to the dotted string ``"1.3.6.1.4.1.311.60.2.1.1"``.

.. attribute:: JURISDICTION_STATE_OR_PROVINCE_NAME

Corresponds to the dotted string ``"1.3.6.1.4.1.311.60.2.1.2"``.

.. attribute:: BUSINESS_CATEGORY

Corresponds to the dotted string ``"2.5.4.15"``.

.. attribute:: POSTAL_ADDRESS

.. versionadded:: 1.6

Corresponds to the dotted string ``"2.5.4.16"``.

.. attribute:: POSTAL_CODE

.. versionadded:: 1.6

Corresponds to the dotted string ``"2.5.4.17"``.

.. class:: SignatureAlgorithmOID

.. versionadded:: 1.0

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: ECDSA_WITH_SHA1

Corresponds to the dotted string ``"1.2.840.10045.4.1"``. This is a SHA1
        digest signed by an ECDSA key.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: DSA_WITH_SHA1

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

.. attribute:: 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.

.. attribute:: 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.

.. class:: ExtendedKeyUsageOID

.. versionadded:: 1.0

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. attribute:: 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.

.. class:: AuthorityInformationAccessOID

.. versionadded:: 1.0

.. attribute:: OCSP

Corresponds to the dotted string ``"1.3.6.1.5.5.7.48.1"``. Used as the
        identifier for OCSP data in
        :class:`~cryptography.x509.AccessDescription` objects.

.. attribute:: 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:`~cryptography.x509.AccessDescription` objects.

.. class:: CertificatePoliciesOID

.. versionadded:: 1.0

.. attribute:: CPS_QUALIFIER

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

.. attribute:: CPS_USER_NOTICE

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

.. attribute:: ANY_POLICY

Corresponds to the dotted string ``"2.5.29.32.0"``.

.. class:: ExtensionOID

.. versionadded:: 1.0

.. attribute:: BASIC_CONSTRAINTS

Corresponds to the dotted string ``"2.5.29.19"``. The identifier for the
        :class:`~cryptography.x509.BasicConstraints` extension type.

.. attribute:: KEY_USAGE

Corresponds to the dotted string ``"2.5.29.15"``. The identifier for the
        :class:`~cryptography.x509.KeyUsage` extension type.

.. attribute:: SUBJECT_ALTERNATIVE_NAME

Corresponds to the dotted string ``"2.5.29.17"``. The identifier for the
        :class:`~cryptography.x509.SubjectAlternativeName` extension type.

.. attribute:: ISSUER_ALTERNATIVE_NAME

Corresponds to the dotted string ``"2.5.29.18"``. The identifier for the
        :class:`~cryptography.x509.IssuerAlternativeName` extension type.

.. attribute:: SUBJECT_KEY_IDENTIFIER

Corresponds to the dotted string ``"2.5.29.14"``. The identifier for the
        :class:`~cryptography.x509.SubjectKeyIdentifier` extension type.

.. attribute:: NAME_CONSTRAINTS

Corresponds to the dotted string ``"2.5.29.30"``. The identifier for the
        :class:`~cryptography.x509.NameConstraints` extension type.

.. attribute:: CRL_DISTRIBUTION_POINTS

Corresponds to the dotted string ``"2.5.29.31"``. The identifier for the
        :class:`~cryptography.x509.CRLDistributionPoints` extension type.

.. attribute:: CERTIFICATE_POLICIES

Corresponds to the dotted string ``"2.5.29.32"``. The identifier for the
        :class:`~cryptography.x509.CertificatePolicies` extension type.

.. attribute:: AUTHORITY_KEY_IDENTIFIER

Corresponds to the dotted string ``"2.5.29.35"``. The identifier for the
        :class:`~cryptography.x509.AuthorityKeyIdentifier` extension type.

.. attribute:: EXTENDED_KEY_USAGE

Corresponds to the dotted string ``"2.5.29.37"``. The identifier for the
        :class:`~cryptography.x509.ExtendedKeyUsage` extension type.

.. attribute:: AUTHORITY_INFORMATION_ACCESS

Corresponds to the dotted string ``"1.3.6.1.5.5.7.1.1"``. The identifier
        for the :class:`~cryptography.x509.AuthorityInformationAccess` extension
        type.

.. attribute:: INHIBIT_ANY_POLICY

Corresponds to the dotted string ``"2.5.29.54"``. The identifier
        for the :class:`~cryptography.x509.InhibitAnyPolicy` extension type.

.. attribute:: OCSP_NO_CHECK

Corresponds to the dotted string ``"1.3.6.1.5.5.7.48.1.5"``. The
        identifier for the :class:`~cryptography.x509.OCSPNoCheck` extension
        type.

.. attribute:: CRL_NUMBER

Corresponds to the dotted string ``"2.5.29.20"``. The identifier for
        the ``CRLNumber`` extension type. This extension only has meaning
        for certificate revocation lists.

.. attribute:: POLICY_CONSTRAINTS

Corresponds to the dotted string ``"2.5.29.36"``. The identifier for the
        :class:`~cryptography.x509.PolicyConstraints` extension type.

.. class:: CRLEntryExtensionOID

.. versionadded:: 1.2

.. attribute:: CERTIFICATE_ISSUER

Corresponds to the dotted string ``"2.5.29.29"``.

.. attribute:: CRL_REASON

Corresponds to the dotted string ``"2.5.29.21"``.

.. attribute:: INVALIDITY_DATE

Corresponds to the dotted string ``"2.5.29.24"``.

Helper Functions
~~~~~~~~~~~~~~~~
.. currentmodule:: cryptography.x509

.. function:: random_serial_number()

.. versionadded:: 1.6

Generates a random serial number suitable for use when constructing
    certificates.

Exceptions
~~~~~~~~~~
.. currentmodule:: cryptography.x509

.. 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
    that is marked ``critical``.

.. 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`_.

.. _`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
.. _`CABForum Guidelines`: https://cabforum.org/baseline-requirements-documents/