def get_certificate(context, signature_certificate_uuid):
    """Create the certificate object from the retrieved certificate data.

    :param context: the user context for authentication
    :param signature_certificate_uuid: the uuid to use to retrieve the
                                       certificate
    :returns: the certificate cryptography object
    :raises: SignatureVerificationError if the retrieval fails or the format
             is invalid
    """
    keymgr_api = key_manager.API()

    try:
        # The certificate retrieved here is a castellan certificate object
        cert = keymgr_api.get(context, signature_certificate_uuid)
    except KeyManagerError as e:
        # The problem encountered may be backend-specific, since castellan
        # can use different backends.  Rather than importing all possible
        # backends here, the generic "Exception" is used.
        msg = (_LE("Unable to retrieve certificate with ID %(id)s: %(e)s")
               % {'id': signature_certificate_uuid,
                  'e': encodeutils.exception_to_unicode(e)})
        LOG.error(msg)
        raise exception.SignatureVerificationError(
            reason=_('Unable to retrieve certificate with ID: %s')
            % signature_certificate_uuid)

    if cert.format not in CERTIFICATE_FORMATS:
        raise exception.SignatureVerificationError(
            reason=_('Invalid certificate format: %s') % cert.format)

    if cert.format == X_509:
        # castellan always encodes certificates in DER format
        cert_data = cert.get_encoded()
        certificate = x509.load_der_x509_certificate(cert_data,
                                                     default_backend())

    # verify the certificate
    verify_certificate(certificate)

    return certificate
dataset/ETHPy150Open BU-NU-CLOUD-SP16/Trusted-Platform-Module-nova/nova/signature_utils.py/get_certificate/original