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Posted by John Elsbury on August 13, 2004, 8:01 am
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>I work for a consulting firm, and we send out proposals for our
>services in large quantitities to prospective clients. I need to know
>how we can use digital signatures for verifying our documents,
>specifically to create signed PDFs and /or Office 2000 documents.
>How are these certificates different from SSL certificates? If I buy an
>SSL certificate for my organization, can I use the same thing to sign
>my documents, after importing it?
>Or do you need separate certificates for the purpose?
>
I am not sure that you can sign Office documents or PDF files as such.
You can sign e-mails which have them as attachments, using seure mime,
however - that proves to the recipient that you actually sent the
e-mail message and that it wasn't altered betwween sending and
delivery, but that is all it proves. To do that you need a digital
certificate, have a look at the Verisign web site - there ia a good
FAQ there.
If you want to digitally sign the documents themselves then in the
case of Office documents, the best you can do (I think) is put a
complex password on for read and for update. That way you can be
satisfied that nobody can change the documents and, I suppose, if you
communicate the read password "out of band" to the recipient then they
can have some assurance that it came from you. You may be able to
lock PDF files so that they can't be altered as well but I haven't
looked into how that works or how secure it may be.
A lot depends on what you are trying to prove, and how.
Regards
John
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