As others have said, jamming 3G of data into 1G of ram is going to be problematic ... especially since you're doubling your amount of memory by reading the file into memory first. I would recommend:

1. processing the file line by line

     open( my $fh, "<", $sigDataFile ) || die( "cannot open file - $!" );
     while( <$fh> ) {
        chomp;
        my( $key, $value ) = split(/=/, $_); # does = need to be escaped?
        ...
      }
   [download]

2. use something like SDBM_File or GDBM_File

     use Fcntl;
     use SDBM_File;
   
     tie( %hash, 'SDBM_File', 'temp_file_name', O_RDWR|O_CREAT, 0666 )
       or die "Couldn't tie SDBM file 'filename': $!; aborting";
   
     open( my $fh, "<", $sigDataFile ) || die( "cannot open file - $!" );
     while( <$fh> ) {
       chomp;
       my( $key, $value ) = split( /=/, $_ );
       $hash{$key} = $value;
       ...
     }
   [download]