Authorize.net/CURL/SSL?

[oraknabo]

This is adapted from the anacom curl script for Authorize.net. I am runnung this on a secure page:

$curl = "/usr/local/bin/curl";

$authnet_url = "https://secure.authorize.net/gateway/transact.dll";

  $data  = "x_ADC_Delim_Data=TRUE&";
  $data .= "x_ADC_URL=FALSE&";
  $data .= "x_Login=*ACCOUNT_ID*&";
  $data .= "x_Password=*PASSWORD*&";
  $data .= "x_Version=3.1&";
  $data .= "x_Invoice_Num=$incart[0]&";
  $data .= "x_Amount=$amount&";
  $data .= "x_Method=CC&";
  $data .= "x_Card_Num=$cardnum&";
  $data .= "x_Exp_Date=$expdate&";
  $data .= "x_Email_Customer=TRUE&";
  $data .= "x_Email=$dest[email]";

  $encodeddata = urlencode($data);

  exec("$curl -d \"$encodeddata\" $authnet_url", $return_string);

  for($i=0;$i<count($return_string);$i++)
  {
     echo "$return_string[$i]";
  }

  $auth_status = explode(",", $return_string[0]);

  if($mode == "simple")
  {
     // get the status of the credit card and
     // assign it to the variable card_status
     if($auth_status[0] == "2")
     {
        $card_status = "Declined: $auth_status[3]";
     }
     elseif($auth_status[0] == "1")
     {
        $card_status = "Approved: $auth_status[3]";
     }
     elseif($auth_status[0] == "3")
     {
        $card_status = "Error: $auth_status[3]";
     }
  }

  elseif($mode == "verbose")
  {
     $card_status = $return_string[0];
  }

  // return the card status
  return $card_status;

---

I've checked on the passed variables and the encoded data string and they look OK but I get no return string at all and the transaction doesn't register. What's the deal? Do I need to use OpenSSL or something?