Encrypt an S/MIME message

Description

openssl_pkcs7_encrypt(
    string $input_filename,
    string $output_filename,
    OpenSSLCertificate|array|string $certificate,
    ?array $headers,
    int $flags = 0,
    int $cipher_algo = OPENSSL_CIPHER_AES_128_CBC
): bool

openssl_pkcs7_encrypt() takes the contents of the file named input_filename and encrypts them using an RC2 40-bit cipher so that they can only be read by the intended recipients specified by certificate.

Parameters

input_filename

output_filename

certificate

Either a lone X.509 certificate, or an array of X.509 certificates.

headers

headers is an array of headers that will be prepended to the data after it has been encrypted.

headers can be either an associative array keyed by header name, or an indexed array, where each element contains a single header line.

flags

flags can be used to specify options that affect the encoding process - see PKCS7 constants.

cipher_algo

One of cipher constants.

Return Values

Returns true on success or false on failure.

Changelog

Version	Description
8.1.0	The default cipher algorithm (`cipher_algo`) is now AES-128-CBC (`OPENSSL_CIPHER_AES_128_CBC`). Previously, PKCS7/CMS was used (`OPENSSL_CIPHER_RC2_40`).
8.0.0	`certificate` accepts an OpenSSLCertificate instance now; previously, a resource of type `OpenSSL X.509 CSR` was accepted.

Examples

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");
}
?>