From: attila <attila@primenet.com>
Date: Sat, 30 Dec 1995 07:23:03 +0800
To: "Dr. Dimitri Vulis" <dlv@bwalk.dm.com>
Subject: easy avoidance of PGP signature forgeries and reuse
In-Reply-To: <oTTsgD7w165w@bwalk.dm.com>
Message-ID: <Pine.BSD.3.91.951229172352.26978C-100000@usr5.primenet.com>
MIME-Version: 1.0
Content-Type: text/plain




    START <attila>

	I never paid much attention to the problem other than to avoid 
    it by forcing it --i.e. list the destination and the send inside the
    signature block, thus:

    ----------------- BEGIN PGP SIGNED TEXT

    To: john doe <john@box.com>
    Newsgroups: sci.crypt
    From: jane roe <jane@topsey.turvey.com>
    Subject: that's all folks!

    John, don't darken my door during the Christmas holidays.

	Nevermore.

    jane

    ---------------- BEGIN PGP SIGNATURE

    ERTYUIKJBNM,./34567JM,./

    ---------------- END PGP SIGNATURE

	with e-mail, e-letters, direct faxes, etc. it is to easy to 
    ignore the courtesy header. From a standpoint of security, you have
    blown away each of the attacks outline in your article in so much as 
    the signature will not compute if the courtesy block is omitted.

	personally, I do not think PGP 3 should attempt to solve the 
    problem. Most of the headers involved are applied _after_ the message 
    leaves the mail program; and, PGP interfaces are virtually the same 
    as invoking an alternate editor, which gets you nothing.

    END <attila>


--
--------------------------------------------------------------------
#!/bin/perl -s-- -export-a-crypto-system-sig -RSA-3-lines-PERL
$m=unpack(H.$w,$m."\0"x$w),$_=`echo "16do$w 2+4Oi0$d*-^1[d2%Sa
2/d0<X+d*La1=z\U$n%0]SX$k"[$m*]\EszlXx++p|dc`,s/^.|\W//g,print
pack('H*',$_)while read(STDIN,$m,($w=2*$d-1+length$n&~1)/2)