From: Ron McCoy <rmccoy@mercury.interpath.com>
Date: Fri, 13 Oct 95 08:35:08 PDT
To: cypherpunks@toad.com
Subject: Re: responce to graphic encryption replies
In-Reply-To: <199510130432.AAA14986@thor.cs.umass.edu>
Message-ID: <199510131535.LAA01216@mercury.interpath.net>
MIME-Version: 1.0
Content-Type: text/plain


> 
> Steve Orrin writes:
> [...]
> >     One of the key strengths, as I see it, of graphic encryption is 
> > that during decryption via hacking, there is an added time element when 
> > a human interface is required to verify the product, ( since it is a 
> > graphic picture being produced, regular checksums for intelligible 
> > words can't be used sans implementing OCR), even if this is only 10 
> > milliseconds per try this is increases the time to crack 
> 
> This is an interesting point I hadn't previously considered. Can anyone
> comment on the state of the art in fast approximate character recognition ?
> I expect that the people working on recognition of text in TV pictures etc.
> would have a good idea. 
> 
[....] 
> 
> -Futplex <futplex@pseudonym.com>
> 

I wouldn't think you would have to use OCR to detect a successful 
decryption. The graphic file is going to have a highly correlated 
structure, long runs of white space etc. The statistics for such a file 
would be different than the random distribution you'd get from using the 
wrong key. Even if the graphics format is compressed, leading to a more 
even distribution, there might be known plaintext at the beginning of the 
file, headers, size etc.


Ron McCoy
Rmccoy@mercury.interpath.net