1993-12-15 - Re: Signing pictures – how hard, how long?

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From: kqb@whscad1.att.com
To: cypherpunks@toad.com
Message Hash: 9ef2f7489fe48a75611ae7f7bc939bb4e3c7f0b56363e74fcb2a406424f1f59c
Message ID: <9312150016.AA04637@toad.com>
Reply To: N/A
UTC Datetime: 1993-12-15 00:20:29 UTC
Raw Date: Tue, 14 Dec 93 16:20:29 PST

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From: kqb@whscad1.att.com
Date: Tue, 14 Dec 93 16:20:29 PST
To: cypherpunks@toad.com
Subject: Re: Signing pictures -- how hard, how long?
Message-ID: <9312150016.AA04637@toad.com>
MIME-Version: 1.0
Content-Type: text/plain


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
                              INTERNET    kqb@whscad1.att.com
                                 or       kevin_q_brown@att.com





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