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Re: Quoting Portions of a Signed Document
On Tue, Nov 25, 1997 at 06:49:17PM -0600, William H. Geiger III wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
>
> In <[email protected]>, on 11/25/97
> at 07:02 PM, [email protected] (Anonymous) said:
>
> >It would be nifty if there was a way to show that any continuous set of
> >bits were signed given only one signature on a whole document.
> >Intuitively, it seems to me that this might be provably inconsistent with
> >a secure hash. Still, crypto results are full of surprises, so I could
> >imagine there is a way to do this.
>
> Well you can do it. Wether you want to do it is another matter.
>
> For the level of granularity you are sugesting a hash is not pratical.
>
> You could just use RSA encryption to encrypt the message in the following
> manner:
>
> The user encrypts the message with his *private* key. Rather than
> encrypting the entire document in one operation he would encrypt each
> [insert you level of granularity here] and then concantinate the results.
> Say we wanted a level of granularity of a word:
>
> word1 word2 word3 word4
>
> the resulting cypher text would be:
>
> cypher1 cypher2 cypher3 cypher4
>
> Now if someone wished to verifiably quote words 1,3,4 they would include
> cypher1 cypher3 cypher4 in their document.
>
> Since cypher 1,3,4 could only be generated by original author it can be
> verified that he actually wrote those words.
>
> At a bare minimum this would have to be done on a level of granularity of
> a sentance to have any meaning at all and even then it's relavance would
> be questioned.
The interesting case is when you do it at the granularity of the bit....
--
Kent Crispin "No reason to get excited",
[email protected] the thief he kindly spoke...
PGP fingerprint: B1 8B 72 ED 55 21 5E 44 61 F4 58 0F 72 10 65 55
http://songbird.com/kent/pgp_key.html