Perl brute force attack - perl

Question

I am having a lot of trouble trying to create a brute force script. The password I need to crack is 1 to 4 characters long and all lowercase letters. I think I have figured out the code to generate all the possible combinations but I am not sure how to test this on a file. Any guidance or hints would be great.
$password = "aaaa";
while ( length $password < 5 ) {
print "$password\n";
$password++;

Answer 1

I had this similar problem. Either you are in my class or scripting classes around the country do this problem at the same time. My professor encourages forum use but we can't share answers with direct classmates at our university.
If you know me from your class by my username, then I ask that you do not use my code. Otherwise enjoy. I have commented the code since learning from working code is the best way to learn.
As long as you are using only letters you can just increment a scalar instead of nesting loops. If you do need to use other characters I bet you could just use an array of possible characters and increment through that array for each position, though let's ignore that since you seem to only need those letters =)
sub brute2()
{
print "Bruteforce Attack...\n";
print "Enter password length: "; #Prompt user for maximum length for pass
chomp(my $plen = (<>)); #Receive input and remove newline character
print "Password Length is $plen\n";
$plen++;
print "Press any key to continue.\n"; #Execute once they hit any key
if (<>)
{
my $pass = "a"; #This code assumes only letters a..z, so we just set here
while ( length $pass < $plen ) #Run check loop until we exaust all possibilities within the maximum length
{
my $status = system("unzip -pp -o -P $pass secret_file_brute.zip > /dev/null 2>&1"); #System call to compare our password against a zip file, this will set status to the return value
print ("Attempting: $pass Return: $status\n");
if ($status == 0) #Return value of 0 means success
{
print ("Password is: $pass Return is: $status\n"); #Print correct password. I did return value also for debug
last; #Break loop since we got correct password
}
$pass++; #Increment $pass var to next iteration IE "a" to "b", "aa" to "ab", "zzz" to "aaaa" etc...
}
}
}

Answer 2

According to the man page I found, unzip returns exit code 82 when it can't decrypt.
sub try {
my ($password) = #_;
system("unzip -qq -o -P $password secret_file_brute.zip >/dev/null 2>&1");
die("Can't launch unzip: $!\n") if $? == -1;
die("unzip killed by signal ".($? & 0x7F)."\n") if $? & 0x7F;
my $exit_code = $? >> 8;
die("unzip exited with error $exit_code\n") if $exit_code && $exit_code != 82;
return !$exit_code;
}
Your code does not generate all of the possible passwords (e.g. it doesn't generate aaa). The following does:
sub brute_force {
for (my $password = 'a'; length($password)<5; ++$password) {
return $password if try($password);
}
return undef;
}
The final bit is to display the results.
{
my $password = brute_force();
defined($password)
or die("Password not found\n");
print("$password\n");
}