openssl_pkcs7_verify

mixed openssl_pkcs7_verify ( string $filename , int $flags [, string $outfilename [, array $cainfo [, string $extracerts [, string $content ]]]] )

Verifies the signature of an S/MIME signed message

openssl_pkcs7_verify() reads the S/MIME message contained in the given file and examines the digital signature.

There is a hidden sixth argument: string pointing to a file where the contents of the signed message should be saved.

 
openssl_pkcs7_sign(
    "full_path_to_message_file", 
             
    "full_path_where_to_store_signed_message_file", 
     "file://full_path_to_my_public_certificate.pem", 
     array("file://full_path_to_my_private_key.pem", "password"),
     array(),
     0);

5.1.0 The content parameter was added.