sub writeSubmissions {
   my ($cipher, $log_file, $str) = @_;

   open(my $FH_encrypted, '>>', $log_file)
      or die;
   binmode $FH_encrypted;
   flock $FH_encrypted, LOCK_EX;

   write_str($FH_encrypted, $cipher->encrypt($str));
}

my $key_file = 'key_file.txt';
my $act_log_file = "pem.enc";
my $pem_log_file = "act_encrypted.enc";

my $my_key = `openssl enc -bf-cbc -d -in \Q$key_file\E -k encrypt`;
my $cipher = Crypt::CBC->new({ key => $my_key, cipher => 'Rijndael' });

writeSubmissions($cipher, ..., ...);