Re: Just a thought...

From: David A. Scott (daVvid_a_scott_at_email.com)
Date: 11/03/03 

Date: 3 Nov 2003 13:07:52 GMT

Peter <peter_rabbit@shaw.ca> wrote in
news:yWkpb.266321$pl3.224340@pd7tw3no:

> somebody in this group, a while back wrote something that germinated in
> me since and finally it dawned...
> the point...
> bytes in block ciphers are interdependent, so if you change one you
> affect all other bytes.
> HOW WONDERFUL!
> So, after encrypting a file, i open it with a hex editor and change the
> value of a few, carefully noted, values by 1,2,3,... whatever.
> So even if the password (in a symetric cipher) is brute forced, the
> decrypted file will be garbage. Obviously, the receiving party would
> need to be aware of which bytes were changed and by how much, otherwise
> they'd have the same problems.
> Any thoughts?
> Peter Radddatz
>

   Its a great idea if its done secretly. However to make it a better
idea apply bijective arithmetic compression or bijective PPM compression
like in BICOM before the encryption. Then change not only certain values
as before but at least one value based on there position of being in
the first 16 bytes so that the change would affect the whole file. That
way even if the correct key was used say for a CBC AES type of encryption
even if a string of several blocks not changed by decryption process
they would still appear meaningless and the reverse bijective compression
would not help at all. You don't get any meaningful results anywhere in
the file untill the changes in first block fixed before the correct key
is applied.

  You also instead if changing the compressed file before encryption
you could rotate the file using DSC or you could add a secret number
of character before the file. As in my example for how two lovers could
secretly communicate. See URL
http://bijective.dogma.net/compres2bse.htm
where the message
"I WILL SEE YOU AT NOON DO NOT TELL YOUR DAD"
becomes
"ATHEG SNCREVES N THAGLING IND RLYSHERAS MMOW HE S S IA"
In the above example the output looks like english to
second order and a cryptologist would swear its some
easy toy form of encryption but it was nothing other
than a few bijective compression/decompressions where
the only secrect was the the 3 letters "SEX" where added
at one stage. It has built in authenication in that on
decrption if the word "SEX" does not appear at the correct
place the message is a forged. ( to use as a real
authentication you would need to reverse file a add extra stage)
  The point is at various stages you could do bijective
transforms with modification in what I would call a
STEALTH ENCRYPTION in that it could lead an attacker
to think you did something else. But its different than
the usual game played here you have to keep the revised
method secret. Here we pretend everything is known except
the key. In real life these minor changes can be thought
of has an extended key which greatly complicates things
if the attacker not bright enough to guess you did something
nonstandard.

David A. Scott 

-- 
My Crypto code
http://cryptography.org/cgi-bin/crypto.cgi/Misc/scott19u.zip
http://cryptography.org/cgi-bin/crypto.cgi/Misc/scott16u.zip
http://www.jim.com/jamesd/Kong/scott19u.zip old version
My Compression code http://bijective.dogma.net/
**TO EMAIL ME drop the roman "five" **
Disclaimer:I am in no way responsible for any of the statements
 made in the above text. For all I know I might be drugged.
As a famous person once said "any cryptograhic
system is only as strong as its weakest link"

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