The safer way to encrypt

Related to my last question i have a new one.

What is a safer way to send encrypted data via https.

using signAndEncrypt function with openssl_pkcs7_encrypt and send return array via form element...

$encryptedData = "-----BEGIN PKCS7-----" . str_replace("\n", "", <br/>   $encryptedDataReturn['encrypted_data']) ."-----END PKCS7-----";

    $encryptedRequest=<<<PPHTML
  <html>
    <header>
    </header>

    <body onload="document.getElementById('paypal_form').submit();">
      <br/><br/><br/><br/>
      <center>
        <h2>Please wait, your order is being processed and you
            will be redirected to the paypal website.
        </h2>
      </center>
      <form id="paypal_form" method="POST" action="{$this->gatewayUrl}">
        <input type="hidden" name="cmd" value="_s-xclick">
        <input type="hidden" name="encrypted" value="$encryptedData">
      </form>
    </body>
  </html>

PPHTML;

or using curl like this

$curlOptions = array (
            CURLOPT_URL => Config::MERCHANT_SANDBOX_SIGNATURE_ENDPOINT,
            CURLOPT_VERBOSE => 1,
            CURLOPT_SSL_VERIFYPEER => true,
            CURLOPT_SSL_VERIFYHOST => 2,
            CURLOPT_CAINFO => $this->publicCertificate,
            CURLOPT_RETURNTRANSFER => 1,
            CURLOPT_POST => 1,
            CURLOPT_HEADER => true,
            CURLOPT_POSTFIELDS => http_build_query($data)
    );


    $ch = curl_init();
    curl_setopt_array($ch,$curlOptions);

    //Sending our request - $response will hold the API response
    $response = curl_exec($ch);

I'am trying to find the safest way to send data to the paypal api. First i mixed both of the functions, and added the encrypted nvp to the CURLOPT_POSTFIELDS. But that gave me a bunch of errors from paypal. So i have done a double encryption. When i leave the postfields unencrypted, the paypal api gives me success.

My Questions:
1. Is it secure enough, to use curl with public certificate ?
2. Is it possible to use the pkcs7 encryption (or similar encryption) with curl?
3. Am I right in assuming that it isnt possible to encrypt the postfields, before send data via curl/https to paypal, because when i do that, paypal give me failure responses?

Please help.
Greetings ninchen

When it comes to crypto & security, your first answer should be to do whatever is standard. It's standard for a reason, and can be expected to be reasonably secure. If vulnerabilities are discovered, you'll need to update, but then again so will everyone else. Trying a clever trick to be "more secure" usually means that you end up with something that is less so.

See this answer for an extended discussion.