From: Sergey Goldgaber <sergey@delbruck.pharm.sunysb.edu>
Date: Wed, 23 Feb 94 20:22:35 PST
To: Matt Thomlinson <phantom@u.washington.edu>
Subject: Re: STEALTH OCEANS
In-Reply-To: <Pine.3.89.9402231824.A3563-0100000@stein3.u.washington.edu>
Message-ID: <Pine.3.89.9402232236.B2157-0100000@delbruck.pharm.sunysb.edu>
MIME-Version: 1.0
Content-Type: text/plain




On Wed, 23 Feb 1994, Matt Thomlinson wrote:

> On Wed, 23 Feb 1994, Sergey Goldgaber wrote:
> 
> > They would.  But, combined with "Stealth PGP" (ie. encryption without 
> > telltale headers) searching through all the deleted noise (which could be 
> > legitimate for all they know) would be futile.
> 
> I can see how a stealth-PGP would allow you to hide messages on your disk 
> in "wiped" filespace 

No, no.  The function of Stealth PGP is, as I understand it, to simply 
encrypt plaintext into something that is virtually indistinguishable
from noise.  Deleting those "noise" files is a seperate issue.

>                     -- it'd look like garbage (maybe -- see Aside), if 
> anyone took a look. What does this buy you, though, if you've got a 
> telltale TSR hanging around?
>

What telltale TSR?  A program that can read and write directly to disk?
If I am not mistaken, such programs are common enough not to be
evidence of anything.  Having PGP on you is another matter, however.

> 
> > > Another thing that has bothered me: if you didn't have the sectors marked,
> > > you'd need to remember where they were (so you could protect them from
> > > writes). You wouldn't necessarily want to do this on the computer; it'd be
> > > there for the picking. How to do it?
> > > 
> > 
> > Simple.  You would take note of the starting address of the file.  And, 
> > the length of the file.
> 
> 
> how do you control individual writes? 

With a standard direct disk read/write utility.

>                                      You've got to know where they are 
> vs. where your data is kept. Authorize each write by hand? (PROGMAN.EXE 
> is attempting to write to cylinder 12, track 14. Authorize (y/N)? ) 
> 
> Icky. 
> Do it another way? See below.
> 

Disable authorization.  Most DOSs allow direct writes without 
authorization anyway.

> 
> > everyone keeps hiding their data in the same location it will not remain
> > hidden for long.
> 
> 
> exactly my point. It seems you've got to have one of two things with your 
> system: 
> 
> 1) a standard place where you hide your noise file (for example, use 
> norton to defrag and compress your disk, then ALWAYS write your noise 
> file on the last two cylinders.) 
> 

This is not necessary.  In fact, as I noted, hiding your files in the 
same place everytime lessens security.  The alternative is a simple one.
Hide your files in different places, and keep track of them.  For 
example, a file that was encrypted on 02-23-94 could be written to disk 
starting with sector 022394.  All you have to do is remember the date and 
length of the file to retrieve it successfully.

> Problem: Needs some program to revive the info; this is a tip-off... Also,
> once your stealth system becomes known, the reason for hiding the noise 
> file is gone -- the tracks/cyl will be checked if they find the reviving 
> program. Instant noise file. 
> 

Again, the program would be a standard utility that can write/read to/from
the disk.  One has to tell the program what tracks/sectors to 
read/write.  Having the program without the corresponding file 
address/length is useless.

> 
> 
> 2) a non-standard place/way to hide your noise file (for example, using a 
> TSR with the areas not to write being protected; using the TSR when you 
> need to restore the data later). 
> 
> Problem: Needs program in memory (or info on disk about where it resides) 
> to revive the data later. A tip-off that again defeats the purpose of 
> hiding the noise file.
> 

You need _not_ have a TSR with the location.  If you keep track of the 
address/length yourself, the problem is eliminated.  The whole
automated (TSR) idea is only usefull if you are frequently accessing your 
disk.  In that case, saving your encrypted files to RAM temporarily might 
be a more elegant solution.  Otherwise, store your "noise" files 
sequentially, on a floppy that you use only for storing encrypted data.  
Guard their respective addresses/lengths as dearly as you would your secret 
key and it's corresponding password.

> 
> 
> Analysis: It seems with the systems I can think of you need to have the
> area the noise file stored in either 1) standard (ick) or 2) kept in
> memory so you don't overwrite it. If you don't protect it, I wouldn't
> expect your noise file to have a very large half-life. :l Keeping the area
> in memory (under protection) defeats the system. 
> 

I'm sorry, this paragraph just went over my head.  Could you restate it 
in another way, so I can attempt to comment?

> 
> 
> Aside: By the way, isn't the "noise" in your noise file is going to be
> more random looking than other deleted areas of your disk? PGP compresses
> and then encrypts; I'll bet that it is possible to distinguish pgp's
> output bit frequencies from those of a binary or text file, which is what
> the rest of the wiped space would most likely be. 
> 

Absolutely!  I have anticipated this problem; and, have been awaiting an
opportunity to address it.

Steps must be taken to keep the deleted portion of your disk from looking 
too random.  In order to implement this additional level of security 
(through obscurity ;) one could:

 1 split the "noise" file into smaller parts which would be interspersed 
   randomly among the other deleted grabage.  This would make for a less 
   conspicuous disk; as, there are, normally, truely random sections of 
   the disk along with the not-so-random sections.  Your bits of noise-file
   will fit right in!

or

 2 use a steganorgraphy utility to embed the "noise" file in a section
   of the other not-so-random garbage (as some people currently use those
   same utilities to embed their PGP files in GIFs), and then delete it.
   (Owning a stegonagraphy utility would, of course, be as conspicuous
    as owning PGP.  So the same precautions would have to be applied.)

These options are very similar.  I prefer the former.  Relying on a stego 
utility seems to be as unreasonable as relying on a TSR to keep track of 
the location of your deleted "noise" files.  I would split and hide the 
"noise" file by hand, and keep track of its location by hand as well, to 
ensure maximum security.

Alternatively, one could use a "Mimic" function with a "DOS garbage" grammar.
This is effectivaly the same as option 2.

> 
> mt
> 
> Matt Thomlinson                               Say no to the Wiretap Chip!
> University of Washington, Seattle, Washington.
> Internet: phantom@u.washington.edu      	    phone: (206) 548-9804
> PGP 2.2  key available via email or finger phantom@hardy.u.washington.edu
> 
> 

Thanks for your input, once again, Matt!


Sergey