[FYI] (Fwd) FC: MIT programmers create 7-line Perl app that decrypts

["Axel H Horns" <horns@ipjur.com>]

------- Forwarded message follows -------
Date sent:      	Wed, 7 Mar 2001 17:45:19 -0500
From:           	Declan McCullagh <declan@well.com>
To:             	politech@politechbot.com
Copies to:      	sipb-iap-dvd@mit.edu
Subject:        	FC: MIT programmers create 7-line Perl app that decrypts DVDs
Send reply to:  	declan@well.com



http://www.wired.com/news/culture/0,1284,42259,00.html

   Descramble That DVD in 7 Lines
   by Declan McCullagh (declan@wired.com)
   9:00 a.m. Mar. 7, 2001 PST

   CAMBRIDGE, Mass. -- Descrambling DVDs just got even easier, thanks
   to a pair of MIT programmers.

   Using only seven lines of Perl code, Keith Winstein and Marc
   Horowitz have created the shortest-yet method to remove the thin
   layer of encryption that is designed to prevent people -- including
   Linux users -- from watching DVDs without proper authorization.

   Their "qrpff" program is a more compact cousin of the DeCSS utility
   that eight movie studios successfully sued to remove from the
   website of 2600 Magazine. But unlike DeCSS, qrpff is abbreviated
   enough for critics of the Motion Picture Association of America to
   include in, for example, e-mail signature files -- and many already
   have.

   "I think there's some value in demonstrating how simple these
   things really are and how preposterous it is to try to restrict
   their distribution," says Winstein, a 19-year-old MIT sophomore
   computer science major.

   [...]


Usage:
qrpff 153 2 8 105 225 /mnt/dvd/VOB_FILE_NAME | extract_mpeg2 |
mpeg2_dec -


#!/usr/bin/perl -w
# 531-byte qrpff-fast, Keith Winstein and Marc Horowitz
# <sipb-iap-dvd@mit.edu> MPEG 2 PS VOB file on stdin -> descrambled
# output on stdout arguments: title key bytes in least to
# most-significant order
$_='while(read+STDIN,$_,2048){$a=29;$b=73;$c=142;$t=255;@t=map{$_%16or
$t^=$c^=(
$m=(11,10,116,100,11,122,20,100)[$_/16%8])&110;$t^=(72,@z=(64,72,$a^=1
2*($_%16
-2?0:$m&17)),$b^=$_%64?12:0,@z)[$_%8]}(16..271);if((@a=unx"C*",$_)[20]
&48){$h
=5;$_=unxb24,join"",@b=map{xB8,unxb8,chr($_^$a[--$h+84])}@ARGV;s/...$/
1$&/;$
d=unxV,xb25,$_;$e=256|(ord$b[4])<<9|ord$b[3];$d=$d>>8^($f=$t&($d>>12^$
d>>4^
$d^$d/8))<<17,$e=$e>>8^($t&($g=($q=$e>>14&7^$e)^$q*8^$q<<6))<<9,$_=$t[
$_]^
(($h>>=8)+=$f+(~$g&$t))for@a[128..$#a]}print+x"C*",@a}';s/x/pack+/g;ev
al




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