[598] in Cypherpunks
Re: Steganography
daemon@ATHENA.MIT.EDU (peter honeyman)
Wed May 26 00:07:21 1993
From: peter honeyman <honey@citi.umich.edu>
To: wcs@anchor.ho.att.com
Cc: cypherpunks@toad.com
Date: Tue, 25 May 1993 23:57:52 -0400
In-Reply-To: Your message of Tue, 25 May 1993 21:34:35 -0400.
> A more serious concern is compressibility -
> a real image file is probably more compressible than a file with the
> low-order bit replaced by a crypto-bit, since the real data has moderate
> correlation and the crypto-bits are random. I doubt the Feds will immediately
> start looking to see if you're shipping GIF files that have significantly
> worse compression than average, but they'd probably find something if they did it.
how many bits are we talking about here? suppose it's two in sixteen.
7/8 of the compressible bits remain. so if the normal compressibility
is 2:1, taking two out of sixteen bits would leave 1.75:1 compression.
is that a "notable" difference?
i haven't been paying close enough attention -- is two out of sixteen
a realistic amount? it seems high to me. if it's one out of sixteen,
the effect is only a 6.25% reduction in compression. is that notable?
peter
