(PHP 4 >= 4.0.6, PHP 5, PHP 7)
Sign an S/MIME message
bool openssl_pkcs7_sign ( string $infilename, string $outfilename, mixed $signcert, mixed $privkey, array $headers [, int $flags = PKCS7_DETACHED [, string $extracerts ]] )
openssl_pkcs7_sign() takes the contents of the file named infilename and signs them using the certificate and its matching private key specified by signcert and privkey parameters.