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
# 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^=12*($_%16
-2?0:$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;eval
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