code: def _find_cert_in_list(cert, issuer, certificate_list, crl_issuer):
      revoked_certificates = certificate_list['tbs_cert_list']['revoked_certificates']
      cert_serial = cert.serial_number
      issuer_name = issuer.subject
      known_extensions = set([
          'crl_reason',
          'hold_instruction_code',
          'invalidity_date',
          'certificate_issuer'
      ])
      last_issuer_name = crl_issuer.subject
      for revoked_cert in revoked_certificates:
          if revoked_cert.critical_extensions - known_extensions:
              raise NotImplementedError()
          if revoked_cert.issuer_name and revoked_cert.issuer_name != last_issuer_name:
              last_issuer_name = revoked_cert.issuer_name
          if last_issuer_name != issuer_name:
              continue
          if revoked_cert['user_certificate'].native != cert_serial:
              continue
          if not revoked_cert.crl_reason_value:
              crl_reason = crl.CRLReason('unspecified')
          else:
              crl_reason = revoked_cert.crl_reason_value
          return (revoked_cert['revocation_date'], crl_reason)
      return (None, None)