Qrpff

qrpff is a perl script created by Keith Winstein and Marc Horowitz of the MIT SIPB. It performs DeCSS in six or seven lines. The name itself is an encoding of "decss" in rot-13.

In fact, two versions of qrpff exist: a short version (6 lines) and a fast version (7 lines). Both appear below.

Short:

#!/usr/bin/perl # 472-byte qrpff, Keith Winstein and Marc Horowitz # MPEG 2 PS VOB file -> descrambled output on stdout. # usage: perl -I :::: qrpff # where k1..k5 are the title key bytes in least to most-significant order s"$/=2048;while(<>){G=29;R=142;if((@a=unqT="C*",_) [20] &48){D=89;_=unqb24,qT,@ b=map{ord qB8,unqb8,qT,_^$a [--D] }@INC;s/...$/1$&/;Q=unqV,qb25,_;H=73;O=$b [4] <<9
256|$b [3] ;Q=Q>>8^(P=(E=255)&(Q>>12^Q>>4^Q/8^Q))<<17,O=O>>8^(E&(F=(S=O>>14&7^O) ^S*8^S<<6))<<9,_=(map{U=_%16orE^=R^=110&(S=(unqT,"xb tdxbzx14d") [_/16%8] );E ^=(72,@z=(64,72,G^=12*(U-2?0:S&17)),H^=_%64?12:0,@z) [_%8] }(16..271)) [_] ^((D>>=8 )+=P+(~F&E))for@a [128..$#a] }print+qT,@a}';s/ [D-HO-U_] /$$&/g;s/q/pack+/g;eval

Fast: #!/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

The fast version is actually fast enough to watch a movie with.

See also

* DeCSS

External links

* [http://perl.plover.com/qrpff/ qrpff (fast) explained]
* [http://www-2.cs.cmu.edu/~dst/DeCSS/Gallery/index.html Gallery of CSS descramblers]