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

[kqb@whscad1.att.com]

Alan (Miburi-san) Wexelblat <wex@media.mit.edu> said:
> The problem with bit-rot is a more significant one.  In this case you might
> want to compute your hash not over every bit of the image, but over the
> "significant" ones.  That way if you lose low-order bits that no one cares
> about your signature is still valid.

If your signature does not include the low order bits of your image,
then someone could embed a secret message in those low order bits
(via Romana Machado's "Stego," for example) and your signature still
would be valid.  I wouldn't want my signature over someone else's
steganized message.

I'm sure there's a simple fix for that, such as ensuring enough bit rot
to blow away any but the most error-tolerant steganography or including
a disclaimer of responsibility for the low-order bits, but I couldn't
resist pointing it out.

                              Kevin Q. Brown
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