Am 22.12.2015 um 11:50 schrieb Andreas Lehmkuehler:
Hi,
Am 21.12.2015 um 23:52 schrieb Tilman Hausherr:
In PDFBOX-2801 and PDFBOX-2469
<https://issues.apache.org/jira/browse/PDFBOX-2469> code has been
inserted that
the signature dictionary not be decrypted. What is the reason this is
done,
where can this be found in the specification? I didn't find it.
When looking at the file from PDFBOX-2711, I can't see the signature
details
because these are encrypted.
See here:
Root/Pages/Kids/[0]/Annots/[0]/T
Root/Pages/Kids/[0]/Annots/[0]/V/Location
Root/Pages/Kids/[0]/Annots/[0]/V/
Root/Pages/Kids/[0]/Annots/[0]/V/Name
Root/Pages/Kids/[0]/Annots/[0]/V/Reason
these elements can be displayed if this line in
SecurityHandler.decryptDictionary
if (!COSName.SIG.equals(dictionary.getItem(COSName.TYPE)) &&
!COSName.SIG.equals(dictionary.getItem(COSName.FT)))
is removed.
Why these thoughts? I was looking at the file
Scan0001_protected_signed in
PDFBOX-2729 and was wondering why this worked at all.
Hmm, I can't remember the details, it seems to be a combination of a
misleading comment in the code, a missing double check if the comment
is ok and a misunderstanding that a signature dictionary isn't an
encryption dictionary.
However in hindsight the decision was wrong. As Maruan already found
out, any hexadecimal strings representing the value of the Contents
key in a Signature dictionary must not be encrypted.
@Tilman: Are you going to adjust the code, as you are already in the
middle of testing it?
Yes I'm intending to change the code, but wanted to find more files
first and get feedback (which I got now). Also need to do tests, i.e.
whether the changed code can render all my test files.
I did find more files just now in the digitalcorpora files:
045697.pdf
050289.pdf
070413.pdf
The search program is slow, so I have only three, but all these are
encrypted.
I'll open a new issue later today with my thoughts and some sample files.
Tilman
Tilman
BR
Andreas
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