Re: Signing pictures -- how hard, how long?

[sdw@meaddata.com (Stephen Williams)]

I doubt if it's that simple:  I'm sure that digital movies will
use compression (mpeg, etc.).  One flipped bit could scramble the
whole frame.  Even with lossless compression, error correction would
be worth adding.

It's going to be much easier to compress to mpeg in hardware than to
design tape that can handle the required frame rate/resolution without
compression.

> 
> 
> I think signing photographs and movie images is a difficult
> problem. Why? Because one flipped bit will completely screw
> up the hash function. Errors on these tapes happen rarely,
> but most video manufacturers aren't really going to bother
> worrying about occasional bit errors because they're usually
> invisible to the eye. Why waste all that extra effort on
> error correction if it's not worth the trouble. So signed
> photographs will also need to contain all of the error 
> correction necessary and that will make them more expensive.
> This isn't any real cost on a general purpose machine, but
> it matters in some places.
> 

sdw
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