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From: CHRIS@engvax.UUCP (Chris Yoder)
Newsgroups: mod.computers.vax
Subject: RE: VMS: LP11s and file security
Message-ID: <8608181756.AA19355@csvax.caltech.edu>
Date: Mon, 18-Aug-86 13:26:28 EDT
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Posted: Mon Aug 18 13:26:28 1986
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> [create Identifiers]
>Then set the ownership of the root directories (or maybe sub-directories) to
>the appropriate identifier and world protection to zip (it does not really
>matter what the protection is on the files and subdirecteries is, since if
>one can't access the root, then the whole tree is inaccessable). 

     Ummm, I believe that that last phrase is in error.  Protecting a file by
it's directory protection *only* is not entirely secure.  If someone gets ahold
of the file-id of the file, they can access the file based on *it's*
protection.  Of course, one cannot do this directly from DCL, and you need to
do some fun calls to RMS in the program that accesses it, but in any given
group of students you have a small subset that are 1) very, very clever and 2)
most interested in breaking into files/systems that they are not supposed to
get access to.  Thus you should always protect each file with the access that
you want *it* to have.

     I haven't seen ACL driven access to a file system drive a system to it's
knees yet.  You only really have to worry about it when you start getting
"long" ACLs on every file.  VMS first checks each ACE in the ACLs in order,
then the UIC based protection.  It stops checking when it hits the first thing
that guarantees access or denys access.  If you set up things right so that the
first ACE checked is the one that is most often used, then I doubt that you
will see any real decrease in performance, unless you are accessing a lot of
files over a short period of time.  (I guess what I'm saying is, don't be
afraid to use ACLs, just use them sparingly and efficiently.)

-- Chris Yoder			UUCP -- {allegra|ihnp4}!scgvaxd!engvax!chris 
   Hughes Aircraft Company 	ARPA -- engvax!chris@csvax.caltech.edu