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FC: MIT programmers create 7-line Perl app that decrypts

------- 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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