Hi, I'm trying to sign a pdf document using external hash and signature.
I notice that if i hash the same document (the result of the method
getRangeStream() ) twice, i obtain two different digests.
I suppose that this is becouse the pdf signature methods introduce some
randomness into the document before hashing it.
This is a problem in this case:
- i generate a hash x of the document d
- i send the hash x to a user to make it signed
- i receive the signed hash x and i want to build a signed pdf document with
it.
If i use the code in the example "How to sign with an external signature" (
<http://itextpdf.sourceforge.net/howtosign.html>
http://itextpdf.sourceforge.net/howtosign.html) , specifing
the signed value and the hash x in the method setExternalDigest, i obtain an
invalid signature, becouse the hash calculated by
the PdfAppearence methods is different from the hash x.
Is there a method to rebuild the document corrisponding to the hash x and to
compose a valid pdf signature?
(in some way i want to get the randomness, apply it to the original pdf
document, and build the pdf signature structure).
Thanks
Francesca Merighi
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