236 lines
4.3 KiB
HTML
236 lines
4.3 KiB
HTML
<HTML
|
|
><HEAD
|
|
><TITLE
|
|
>Modem features to restrict usage</TITLE
|
|
><META
|
|
NAME="GENERATOR"
|
|
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
|
|
REL="HOME"
|
|
TITLE="Remote Serial Console HOWTO"
|
|
HREF="index.html"><LINK
|
|
REL="UP"
|
|
TITLE="Security"
|
|
HREF="security.html"><LINK
|
|
REL="PREVIOUS"
|
|
TITLE="Restrict console messages"
|
|
HREF="security-messages.html"><LINK
|
|
REL="NEXT"
|
|
TITLE="BIOS features"
|
|
HREF="security-bios.html"></HEAD
|
|
><BODY
|
|
CLASS="SECTION"
|
|
BGCOLOR="#FFFFFF"
|
|
TEXT="#000000"
|
|
LINK="#0000FF"
|
|
VLINK="#840084"
|
|
ALINK="#0000FF"
|
|
><DIV
|
|
CLASS="NAVHEADER"
|
|
><TABLE
|
|
SUMMARY="Header navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TH
|
|
COLSPAN="3"
|
|
ALIGN="center"
|
|
>Remote Serial Console HOWTO</TH
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="left"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="security-messages.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="80%"
|
|
ALIGN="center"
|
|
VALIGN="bottom"
|
|
>Chapter 9. Security</TD
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="right"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="security-bios.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"></DIV
|
|
><DIV
|
|
CLASS="SECTION"
|
|
><H1
|
|
CLASS="SECTION"
|
|
><A
|
|
NAME="SECURITY-MODEM"
|
|
></A
|
|
>9.5. Modem features to restrict usage</H1
|
|
><P
|
|
>Most modems support the addition of a password. This is not
|
|
particularly useful as it has the same strengths and weaknesses of
|
|
all other password authentication schemes. We already have
|
|
password authentication in the <SPAN
|
|
CLASS="ACRONYM"
|
|
>BIOS</SPAN
|
|
>, in the boot
|
|
loader and in <SPAN
|
|
CLASS="APPLICATION"
|
|
>login</SPAN
|
|
>.</P
|
|
><P
|
|
>Many modems support call-back. The modem is called and a few
|
|
seconds after hang-up it calls a pre-configured number. This
|
|
limits the locations that can gain access to the console. </P
|
|
><P
|
|
>Many modems support checking the calling line identification
|
|
(CLI) against a predefined list. If the calling number is not on
|
|
the list then the call is cleared. The phone line to the modem
|
|
must be configured to send CLI, this may incur an additional charge
|
|
from the phone company. Not all calling phones can send CLI and
|
|
some valid callers may have asked their phone company to suppress
|
|
the sending of CLI.</P
|
|
><P
|
|
>Many modems can be configured to log the calling line
|
|
identification. This is useful when tracing misuse.</P
|
|
><P
|
|
>Many modems support encryption. Some modems allow multiple
|
|
keys. This gives a neat solution: only authorized modems can dial
|
|
in, but they can do so from any location. The modems usually need
|
|
to be of the same make, and perhaps of the same model.</P
|
|
><DIV
|
|
CLASS="WARNING"
|
|
><A
|
|
NAME="WARNING-CRYPTO"
|
|
></A
|
|
><P
|
|
></P
|
|
><TABLE
|
|
CLASS="WARNING"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="25"
|
|
ALIGN="CENTER"
|
|
VALIGN="TOP"
|
|
><IMG
|
|
SRC="../images/warning.gif"
|
|
HSPACE="5"
|
|
ALT="Warning"></TD
|
|
><TH
|
|
ALIGN="LEFT"
|
|
VALIGN="CENTER"
|
|
><B
|
|
>Encryption dual-use technology</B
|
|
></TH
|
|
></TR
|
|
><TR
|
|
><TD
|
|
> </TD
|
|
><TD
|
|
ALIGN="LEFT"
|
|
VALIGN="TOP"
|
|
><P
|
|
>Possessing, using, buying, selling, importing or exporting
|
|
modems with encryption features is a serious criminal offense in
|
|
some countries.</P
|
|
><P
|
|
>You must acquiant yourself with the laws in your
|
|
jurisdiction and the laws of jurisdictions you may travel
|
|
through.</P
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
><P
|
|
>Many telephone services or <SPAN
|
|
CLASS="ACRONYM"
|
|
>PBX</SPAN
|
|
> lines can
|
|
be set to allow only incoming calls. This is useful as it prevents
|
|
misuse of the modem should the computer be compromised. A
|
|
<SPAN
|
|
CLASS="QUOTE"
|
|
>"demon dialler"</SPAN
|
|
> can call many numbers seeking an
|
|
answering modem and the cost of these calls can be
|
|
significant.</P
|
|
></DIV
|
|
><DIV
|
|
CLASS="NAVFOOTER"
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"><TABLE
|
|
SUMMARY="Footer navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="security-messages.html"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="index.html"
|
|
ACCESSKEY="H"
|
|
>Home</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="security-bios.html"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
>Restrict console messages</TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="security.html"
|
|
ACCESSKEY="U"
|
|
>Up</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
><SPAN
|
|
CLASS="ACRONYM"
|
|
>BIOS</SPAN
|
|
> features</TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></BODY
|
|
></HTML
|
|
> |