Hi Rüdiger,
Thanks for the hint. This was indeed the problem. I commited a fix, so that
PoDoFo will get stream length for encrypted streams from PdfEncrypt.
I can load AES encrypted PDFs generated by PoDoFo now, with Acrobat Reader and
Poppler based viewers. Ghostscript still shows errors.
Regards,
Dom
On Monday 23 August 2010 07:25:34 Rüdiger Politzer wrote:
> Hello Dom,
>
> I'm testing the (buggy) AES encryption implementation of libpodofo and I
> hope that I detected the error! The solution is that the length of the
> encrypted object streams has to be adapted.
> That means that not the original stream length should be written in the
> encrypted pdf but the new stream length (including padding and initial
> vector).. You get this new length by calling the CalculateStreamLength()
> function of the PdfEncryptAES class.
>
> My (dirty) solution is to extend the PdfEncrypt class with functions to set
> marker for object streams and object stream length in case of AES
> encryption. First I set the object stream marker in
> PdfObject::WriteObject() in case of object streams and second the object
> stream length marker in PdfDictionary::Write(..). So I got all my
> information and when writting the value of the object stream length in
> PdfVariant::Write() I check for object stream (and AES encryption) and
> adjust the stream length.
> I know that this is certainly a dirty solution but it works and I got
> aes-128bit encrypted pdf's.
> I hope that with this information the AES encryption bug could be fixed in
> a future version of the podofo library. I you want more information or my
> patches just send me an email.
> Best regards
> Rüdiger
>
>
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