php - Any way to encrypt files (and decrypt on the fly) so that they're inaccessible - even by root? -

i have highly confidential documents pertaining stealth mode startup venture. live in directory outside public_html on server @ web host. wrote system allows select people view them (one time - they're not in browser cache) stealth , security, 1 vulnerability have people work @ web host.

i know solve setting own web server in home, (a) it's against isp's tos, , (b) don't have sysadmin chops locking down.

if encrypt them, i'd have able decrypt them on fly people view (once they've signed nda) -- in order decrypt them on fly, i'd have have decryption key (visible) in file somewhere, wouldn't i?

thoughts? comments? suggestions? thanks!

first of all, lets implement system host cannot read files on disk (say, giving authorized user private key need , uploaded encrypted version them). host free sniff out , log outgoing traffic @ hardware or operating system level, defeating scheme completely. if information in clear text @ time on or across hosts hardware, if theirs @ if want so.

the alternative uploading encrypted file specific user, , separately (not using host) sending them private-key need, download host , decrypt on local system. if worry can resend clear text obtain, yes - yes can. if readable in browser, had screen cap or save page out, or use localhost proxy, or half-dozen other options use.

encryption controls access information key-holder - that's it. if there's better that, i'm sure nsa conversation.