openssl_pkcs7_encrypt

bool openssl_pkcs7_encrypt ( string $infile , string $outfile , mixed $recipcerts , array $headers [, int $flags = 0 [, int $cipherid = OPENSSL_CIPHER_RC2_40 ]] )

Encrypt an S/MIME message

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.

// 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 = << "nighthawk@example.com", // keyed syntax
          "From: HQ ", // indexed syntax
          "Subject" => "Eyes only"))) {
    // message encrypted - send it!
    exec(ini_get("sendmail_path") . " < enc.txt");
}

5.0.0 The cipherid parameter was added.