PHP Manual: openssl_pkcs7

Description

bool openssl_pkcs7_encrypt ( string infile, string outfile, mixed recipcerts, array headers [, int flags [, int cipherid]] )

openssl_pkcs7_encrypt() takes the contents of the file named infile and encrypts them using an RC2 40-bit cipher so that they can only be read by the intended recipients specified by recipcerts, which is either a lone X.509 certificate, or an array of X.509 certificates. headers is an array of headers that will be prepended to the data after it has been encrypted. flags can be used to specify options that affect the encoding process - see PKCS7 constants. headers can be either an associative array keyed by header name, or an indexed array, where each element contains a single header line. Cipher can be selected with cipherid since PHP 5.

Example 1. openssl_pkcs7_encrypt() example

<?php
// the message you want to encrypt and send to your secret agent
// in the field, known as nighthawk.  You have his certificate
// in the file nighthawk.pem
$data = <<<EOD
Nighthawk,

Top secret, for your eyes only!

The enemy is closing in! Meet me at the cafe at 8.30am
to collect your forged passport!

HQ
EOD;

// load key
$key = file_get_contents("nighthawk.pem");

// save message to file
$fp = fopen("msg.txt", "w");
fwrite($fp, $data);
fclose($fp);

// encrypt it
if (openssl_pkcs7_encrypt("msg.txt", "enc.txt", $key,
    array("To" => "nighthawk@example.com", // keyed syntax
          "From: HQ <hq@example.com>", // indexed syntax
          "Subject" => "Eyes only"))) {
    // message encrypted - send it!
    exec(ini_get("sendmail_path") . " < enc.txt");
}
?>