6. Security Considerations
Contrast all this with the far more cursory treatment in "IFAX service of ENUM":
DNS, as used by ENUM, is a global, distributed database. Thus any
information stored there is visible to anyone anonymously. Whilst
this is not qualitatively different from publication in a Telephone
Directory, it does open the data subject to having "their"
information collected automatically without any indication that this
has been done or by whom.
Such data harvesting by third parties is often used to generate
lists of targets for unrequested information; in short, they are
used to address "spam". Anyone who uses a Web-archived mailing list
is aware that the volume of "spam" email they are sent increases
when they post to the mailing list; publication of a telephone
number in ENUM is no different, and may be used to send "junk faxes"
or "junk SMS" for example.
Many mailing list users have more than one email address and use
"sacrificial" email accounts when posting to such lists to help
filter out unrequested emails sent to them. This is not so easy with
published telephone numbers; the PSTN E.164 number assignment
process is much more involved and usually a single E.164 number (or
a fixed range of numbers) is associated with each PSTN access. Thus
providing a "sacrificial" phone number in any publication is not
Due to the implications of publishing data on a globally accessible
database, as a principle the data subject MUST give their explicit
informed consent to data being published in ENUM.
In addition, they should be made aware that, due to storage of such
data during harvesting by third parties, removal of the data from
publication will not remove any copies that have been taken; in
effect, any publication may be permanent.
However, regulations in many regions will require that the data
subject can at any time request that the data is removed from
publication, and that their consent for its publication is
explicitly confirmed at regular intervals.
When placing a voice or video call via the PSTN or sending a message
via the Public Land Mobile Network, the sender may be charged for
this action. In both kinds of network, calling or messaging to some
numbers is more expensive than sending to others; both networks have
"premium rate" services that can charge considerably more than a
"normal" call or message destination. As such, it is important that
the end user be asked to confirm sending the message, and that the
destination number be presented to them. It is the originating
user's choice on whether or not to place a call to this destination
number, but they SHOULD be shown the destination number so that they
can make this decision
Where voice or video terminals are configured to accept incoming
calls, there SHOULD be an indication presented to the user that an
incoming call is being offered. Particularly with some video
systems, the terminal may be configured to "auto-accept" the call.
In this case there MUST be an obvious indication presented to the
calling user that this has been done.
Systems configured to auto-accept audio/video calls that are sent to
a number published in a global public directory may be used by
unexpected individuals to check for the presence or otherwise of
people for with a view to stealing property or other unwelcome acts.
Whilst "security through obscurity" may have seemed acceptable when
the access address was known to only a few, publication within ENUM
removes the obscurity, so leaving (for example) a "WebCam" switched
on after such publication is even less wise than in other
In addition to the specific security considerations given above, all
security considerations given in RFC2916bis apply.