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>9.12. Countering interception of telephony links</H1
><P
>Modems calls over telephones can be intercepted. This can be
an issue if you do not trust a telecommunications carrier in your
call's path, or if you do not trust the law enforcement agencies
that may request interception facilities from that carrier.</P
><P
>International calls are particularly exposed. Calls which
are routed across satellite or wireless links can be intercepted by
readily-available radio receivers. Calls routed across undersea
links are much more expensive to intercept, so this is probably
limited to national governments, such as those using the <A
HREF="http://cryptome.org/cryptout.htm#Echelon"
TARGET="_top"
>Echelon
system</A
>.</P
><P
>If you do not pass sensitive data over the link, then the
major exposure is typing in your user name and password. Look into
<A
HREF="http://freshmeat.net/projects/pam_skey/"
TARGET="_top"
><SPAN
CLASS="APPLICATION"
><SPAN
CLASS="ACRONYM"
>S/KEY</SPAN
></SPAN
></A
>
or look into <A
HREF="http://inner.net/opie/"
TARGET="_top"
><SPAN
CLASS="APPLICATION"
><SPAN
CLASS="ACRONYM"
>OPIE</SPAN
></SPAN
></A
>
and its related <A
HREF="http://www.tho.org/~andy/pam-opie.html"
TARGET="_top"
><SPAN
CLASS="APPLICATION"
>An
<SPAN
CLASS="ACRONYM"
>OPIE</SPAN
> for
<SPAN
CLASS="ACRONYM"
>PAM</SPAN
></SPAN
></A
>.</P
><P
>These one-time password systems have flaws, a good summary of
these is <I
CLASS="CITETITLE"
>Vulnerabilities in the
<SPAN
CLASS="PRODUCTNAME"
><SPAN
CLASS="ACRONYM"
>S/KEY</SPAN
></SPAN
> one time
password system</I
> by Peiter ‘mudge’
Zatko.</P
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>Cryptographic key material</B
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> </TD
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><P
>Possessing cryptographic key material, such as a one-time
password generator or list of one-time passwords, 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
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><B
>Defeating telecommunications interception</B
></TH
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> </TD
><TD
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><P
>Taking steps to defeat or avoid legislatively-approved
telecommunications interception 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
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