On Thursday, December 21, 2006 10:26 AM [GMT+1=CET], Lívio Cipriano
<[EMAIL PROTECTED]> wrote:
-------- On 21 December 2006 10:17, Harold Fuchs wrote: --------
Seems to me that this is logically impossible. When you (author of
the document) do the calculation, the document does *not* contain
the sum.
Hi Harold,
In fact, your logic it's perfect. Let me reformulate the problem.
I want to write in my document(s) some indisputable mark that that
document was printed from that file. I already have some on that
line. I print the date and time of the last modification and
printing, both in the format yyyymmddhhmmss.
Some more ideas?
Lívio,
I don't think there is a guaranteed way to link a printed document with
an electronic one unless the reader of the printed version also has
(read-only) access to the electronic version.
You could use a watermark. This would help but wouldn't really
*guarantee* anything.
You could insert a hyperlink pointing at a web page which you control
which has a digitally signed copy of the MD5 sum. Of course, you would
have to insert the hyperlink into the document *before* calculating its
MD5 but it (the link) could be of the form
www.livio.com/md5sums.html#doc13 where "doc13" is a the "name" of the
document and also an HTML "name"
(<a name="doc13">MD5_Sum_for_Document_Number_13</a>) in the HTML page.
The problem with this is that if you move the page you break the link
and, therefore, the document authentication. This still wouldn't help
much because you can't calculate the MD5 from a paper copy. It would be
quite good, though, for authenticating the electronic copy.
Hmmm. Food for thought.
Anybody ???
Regards, Harold
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