How to create index for encrypt domino nsf?

I use following command to create index for search for un-encrypt domino nsf.nupdall.exe “search.nsf” -X

I populated some options in search.nsf. E.g. server, directory, index full document and attachements, and searched nsf “Main.nsf”.

But it can not work if Main.nsf encrypted. No error report. But no index generated.

How to create index on encrypted nsf?

Thank you very much for your help.