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.
Returns TRUE on success or FALSE on failure.