re: Stego inside encryption

To take this one step further, has anyone tried to ever use this method as
an encryption method?  You could hide data in a stream of random bits, using
position as the encryption method.  Obviously, the data would not be stored
in packets; rather as single bits strewn throughout the stream.  Even ASCII
characters could be hidden in such a system very well, as the possibility of
choosing the correct 8 bits (extended char set) from the data stream when
any combination has equal potential of being the correct sequence would be
extremely difficult.  Error checking/correcting code could even be used.

Using this system, the placement algorithm would be the focus of attack.  If
an algorithm which has a sufficiently random placement was used, extracting
the correct bits would be difficult.  Another way to increase the security
would be to hide the correct message inside a bitstream created by using
the same method on other similar messages.  (Hiding a real message inside
bogus messages.  Hmm...  Which one's real?)

Patrick

_______________________________________________________________________________
From: Mullen Patrick on Thu, Sep 19, 1996 9:19
Subject: Stego inside encryption
To: Cypherpunks

I know a lot of times the idea behind steganography is to hide the fact that a
secret message is in a seemingly normal file/mail/whatever.  This is good
for avoiding unwanted interest in your file.  The benefit of not having people
attempt to crack you code, added to the strength of the cryptosystem is
wonderful.  However, I propose this--

Don't hide that anything's encrypted!  Rather than hide this fact, throw it
in their face!  I propose hiding an encrypted message inside another 
encrypted message.  Set bits in specific places to data in the real message.
The benefit is Oscar not only doesn't know what the crypto is, he attacks
the wrong message.  Hiding statistically random bits from the true message
in statistically random bits from the masking message shouldn't be too 
hard.

Granted, this scheme doesn't get you past measures designed to keep out all
encrypted messages, and it surely wouldn't keep you message from generating
interest, but it would be very hard to decrypt the message, especially when 
some algorithm is used which (seemingly) randomly selects which bits to use 
for the stego.

Just a thought...  My apologies if someone has already proposed this method.

Patrick

On 19 Sep 1996, Mullen Patrick wrote:

> To take this one step further, has anyone tried to ever use this method as
> an encryption method?  You could hide data in a stream of random bits, using
> position as the encryption method.  Obviously, the data would not be stored
> in packets; rather as single bits strewn throughout the stream.  Even ASCII
> characters could be hidden in such a system very well, as the possibility of
> choosing the correct 8 bits (extended char set) from the data stream when
> any combination has equal potential of being the correct sequence would be
> extremely difficult.  Error checking/correcting code could even be used.
> 
> Using this system, the placement algorithm would be the focus of attack.  If
> an algorithm which has a sufficiently random placement was used, extracting
> the correct bits would be difficult.  Another way to increase the security
> would be to hide the correct message inside a bitstream created by using
> the same method on other similar messages.  (Hiding a real message inside
> bogus messages.  Hmm...  Which one's real?)

I've written something similar to this idea a few years ago. :)  You 
might want to check it out.  Do a net search for WNS210.ZIP at your 
nearest good crypto ftp site.  You might want to try ftp.wimsey.ca.

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Mullen Patrick wrote:
> To take this one step further, has anyone tried to ever use this
> method as an encryption method?  You could hide data in a stream of
> random bits, using position as the encryption method.  Obviously, the 
> data would not be stored in packets; rather as single bits strewn
> throughout the stream.  Even ASCII characters could be hidden in such 
> a system very well, as the possibility of
> choosing the correct 8 bits (extended char set) from the data stream
> when any combination has equal potential of being the correct sequence 
> would be extremely difficult.  Error checking/correcting code could 
> even be used.
> Using this system, the placement algorithm would be the focus of
> attack.  If an algorithm which has a sufficiently random placement was 
> used, extracting the correct bits would be difficult.  Another way to 
> increase the security would be to hide the correct message inside a
> bitstream created by using the same method on other similar messages. 
> (Hiding a real message inside bogus messages. Hmm...Which one's real?)..... some text deleted here....

This sounds like exactly what I've been saying. You could paste the 
message inside or adjacent to the non-text data (and you could bit-pad 
the text before doing so), then move all the bits around, etc.

I'm not sure what was meant by "even ASCII characters could be 
hidden...", since just before you encrypt, everything's ASCII in some 
sense or another.

Dale Thorn wrote:
> 
> Mullen Patrick wrote:
> > To take this one step further, has anyone tried to ever use this
> > method as an encryption method?  You could hide data in a stream of
> > random bits, using position as the encryption method.

It doesn't matter *what* you do with your bits.  The key thing to
remember when analyzing your encryption method is that the foundation
of your security rests on the difficulty of reversing the numeric
sequence that drives the encryption.

If I know you're using this RNG-driven steganographic message mixer,
then if I can break your RNG I'm done.  If I know you're scrambling
bits in a file according to an RNG, if I break your RNG I'm done.
The key is therefore to make the RNG cryptographically secure.  Once
you've done that, then there's questionable value in doing anything
fancier than straight CBC (or something like that) to encrypt your
plaintext.

Note that simple functional composition of one or more simple insecure
RNG's does not necessarily give you a stronger RNG (in fact it usually
doesn't).  Cheap RNG's like what you get from the old UNIX "rand()"
are simple little linear functions, which when composed give you
more simple functions.

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