From: bruce@ais.com (Bruce C. Wright)
Newsgroups: comp.sys.dec,comp.unix.ultrix
Subject: Re: Sanitize End Sectors?
Date: 9 Nov 92 15:44:40 GMT
Organization: Applied Information Systems, Chapel Hill, NC

In article <1992Nov9.155043.4580@relay.nswc.navy.mil>, wdence@nswc-wo.nswc.navy.mil (Walter Dence) writes:
> 
>      I need to send some files out.  I need to wipe the ends of the 
> end-sectors with zeros (or circumflexes, or anything).  This is
> in case there is any sensitive info carried over into them from
> a previous disk volume that had sensitive info.
> 
>      There was a similar flap several months ago over Prodigy.
> 
>      Is there a DCL batch file or other utility to do this?
> 
>      Is there a FAQ for this newsgroup?
> 
>      Is there an Internet FTP site for DEC-VAX stuff?
> 
>      Does "High-Water Marking" have anything to do with this?
> If a disk volume is set to "Overwrite-on-delete", will this fix
> this problem.  Does the VAX environment have these features and are
> they commonly used for this?

Umm.  I'm not sure how to answer this because it's not clear to me
what you're trying to do.  Which operating system are you using?  The
original article was cross-posted to the Ultrix newsgroup, but terms
like `DCL' and `high-water marking' are more commonly associated with
VMS than with Ultrix.  How are you sending the files out?  Tape (and
which tape format if so), FTP, Kermit, or some other mechanism?  It's
really not possible to give a definitive answer without knowing all
these things.

But to give a partial answer to some of the questions:

There is a FAQ for the newsgroup, you might look for it in comp.os.vms
(and/or news.answers) if you want information on VMS.  There are also
several FTP sites for VMS and Ultrix software;  these are all given in
the FAQ and I don't think that it's worth duplicating the information
here (if you have trouble finding a site with the FAQ send me email and
I'll send you a copy of it.  I think it's probably about time for a new
edition so my copy is about a month out of date by now).

As for the questions about high-water marking and erase-on-delete, yes
this is exactly the sort of thing that these features are for, although
it's usually more relevant for security problems _within_ a single
machine rather than files sent outside that machine.  I'm not sure if
Ultrix has all of them but VMS certainly does.  You do have to explicitly
enable them though.

Even if you _don't_ have high-water marking and erase-on-delete enabled
on your machine, it _still_ may not matter as far as security problems
are concerned, depending on how you plan to send the files.  Many file
transfer methods don't transfer records past the end-of-file pointer in
any event, so even if there _is_ sensitive data past the end-of-file
pointer in the original file, it won't make it to the other system.

There should be some documentation on this topic in the VMS or Ultrix
manual set;  that should help answer some of your questions.  If you
still have trouble finding the information you need please give us more
details about what OS you're using and how you're planning to transfer
the files.

Good luck,

Bruce C. Wright
Newsgroups: comp.sys.dec,comp.unix.ultrix