How to edit PDF?

[rpowersau at gmail.com]

On 11/30/05, Tony Arnold <tony.arnold at manchester.ac.uk> wrote:
>
> Derek,
>
> Derek Broughton wrote:
> > It seems that one of us doesn't understand public-key encryption very
> > well :-)  Surely, the idea is that I encrypt the PDF with my _private_
> key,
> > and readers decrypt it with my public key.  They can't, however, change
> the
> > document because they would then need to re-encrypt it with _my_ private
> > key, or any recipient will know it isn't the version I
> published.  afaik,
> > this is a very good way to distribute documents you don't want changed.
>
> This is not right!


Actually, he can do this.


If I encrypt a document to send to you, then I
> encrypt it with your public key and only you can decrypt it with your
> private key.
>
> If you want documents to stay unchanged, but you are not too worried
> about who reads them, then signing them is the answer. I would sign a
> document with my pivate key and anyone can verify that signature using
> my public key.
>
> For top security, one can do both, i.e., encrypt for a given reader(s)
> and sign by the sender. That way secrecy can be preserved as well as
> integrity.
>
> Regards,
> Tony.
> --
> Tony Arnold, IT Security Coordinator, University of Manchester,
> IT Services Division, Kilburn Building, Oxford Road, Manchester M13 9PL.
> T: +44 (0)161 275 6093, F: +44 (0)870 136 1004, M: +44 (0)773 330 0039
> E: tony.arnold at manchester.ac.uk, H: http://www.man.ac.uk/Tony.Arnold
>
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>



--
Regards,
Russ
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