Re: BMP to GJEP conversion

From: IPGrunt (ipso.facto_at_yahoo)
Date: 04/27/05 

Date: Wed, 27 Apr 2005 02:07:21 GMT

On 23 Apr 2005, Mina Doroudi <dormina@helsinki.cc.gatech.edu>
postulated in news:d4f5re$pio$1@solaria.cc.gatech.edu:

> It won't destroy it... you just change that last bit
> (least significant bit) of a byte...
> I guess if you just try it, you'll see, I don't mean actually
> open a jpeg file and change the bits, yeah that will destory the
> file or the colors... like inserting comments in a jpeg file, if you
do it
> with the right sofware, or your own right code, nothing
> would happend take a look at:
>
> http://wwwrn.inf.tu-dresden.de/~westfeld/attacks.html
> www.ws.binghamton.edu/fridrich/ Research/acmwrkshp_version.pdf
> http://en.wikipedia.org/wiki/Steganography
>
>
> -mina
>
> Unruh <unruh-spam@physics.ubc.ca> wrote:
>> Mina Doroudi <dormina@helsinki.cc.gatech.edu> writes:
>
>>>Unruh <unruh-spam@physics.ubc.ca> wrote:
>>>> Mina Doroudi <dormina@helsinki.cc.gatech.edu> writes:
>
>
>>>>>So, in one tupe of steganography (LSP method) it takes the binary
>>>>>representation of the data, and overwrite the least significant of
>>>>>each byte with a bit of message.
>
>>>>>In the articles that I read, they said the compressed file is
better because:
>
>>>> ??? That is silly. If you change bits in a compressed file, you
will almost
>>>> certainly get complete garbage on the decompression. Each bit is
>>>> significant, and there are no insignificant bits.
>
>>>In fact it is very interesting,
>
>>>1. you don't change the compressed file to decompressed, you only
save it in
>>>the lsb of the compressed file, however you can do it on the
original file
>>>also.
>
>
>
>>>2. the whole point of changing the lsb, is that it doesn't change
the color
>>>that much, try it in you computer, open gimp or paint or... and
select a
>>>color and then change the hex val of that color by 1, you can barely
recognize
>>>there was a change if at all!
>
>> Now take a compressed version of that file and change thelsb of some
of the
>> bytes. You will completely destroy the colour in the file.
>
>
>>>any the poit of asking this question what figuring out how actually
>>>compression works... which I'm still wondering...
>
>>>-Mina
>
>>>>>1. the information in the compressed file has already run through
an entropy encoder
>>>>> whose job was to compress out useless information, therefore it
is hard to find
>>>>> those least significant bit for hiding data!
>>>>> -> I dont' see why is this hard, so the least significant
bit is for each byte
>>>>> there is a LSB, so it doesn't matter if the file is
compressed or not!
>>>>> what am I not getting in here??? when it compresses a
file does it care
>>>>> whic bits are useless?? it doesn't seem like it, from
what I read.
>
>>>> No bits are insignificant. While the bit may be a low order bit,
it is as
>>>> important in uncompressing the file as the high order bots.
>
>>>you don't uncompress the file...
>
>>>>>2. the compressed are imune against visual attack, which is when
you filter the
>>>>> non-significant bits, and only look at the significants too see
if they are changed.
>>>>> -> why does it make a difference, when you filter it since
you only see the
>>>>> replacement bits, it doesn't matter what they are
replacing...
>
>>>> No idea what these sentences mean.
>
>
>>>>>I apreciate any kind of help!
>
>>>>>Mina
>
>>>>>--
>>>>>
>>>>> -Mina Doroudi (dormina@cc.gatech.edu)
>
>>>--
>>>
>>> -Mina Doroudi (dormina@cc.gatech.edu)
>

Perhaps if you contact Neil F. Johnson...are you aware of his work? If
not, visit his website: http://www.jjtc.com/

Have fun.
 
-- ipgrunt