Hi all! What am i trying to do? I

ok I found a sample secured pdf <a href="https://uwaterloo.ca/onbase/help/sample-pdf-d

Fail to sign encrypted pdf about podofo HOT 3 OPEN

podofo commented on May 20, 2024 1

Fail to sign encrypted pdf

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Comments (3)

ceztko commented on May 20, 2024

Thank you for the research. Please also attach all the working and non working pdfs so they will be easily inspectable. This is an interesting topic but it's low priority for me and I don't have the resources to do it, right now.

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ferencIOS commented on May 20, 2024

ok I found a sample secured pdf here

These the results:

samplesecured.pdf
samplesecured-Signed-pdfbox.pdf
samplesecured-Signed-podofo.pdf

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ferencIOS commented on May 20, 2024

Hi, I did not forget! I haven't found a solution but I hope to give some useful hints.

Looking at the samplesecured.pdf and the two files signed by pdfbox and by PoDoFo the substantial difference is represented by the object:

6 1 obj
<</CF<</StdCF<</AuthEvent/DocOpen/CFM/AESV3/Length 32>>>>/Filter/Standard/Length 256/O<9EF36ED0D632E6D2F520D564ADDDF94FB3793E667832EBBFC977E0A13AB77A313DF4A2824721DC8FAF533F9B3599DBCC>/OE<3526E597E1D35623A92C61FF651EBE06C541B929C16EDF0106E869F218297E83>/P -3392/Perms<9C2A1F313E4E64608091C22711F6D473>/R 5/StmF/StdCF/StrF/StdCF/U<D2CFC4C207107A06F09ED9EE0F31E1A38B72A3048030F45D88518668F240538291B2B8EB03D7D60C3241776714CB4436>/UE<91D91A1B147CAC7DFE4B24A03A25297B71C5745DE8A387F7461A0F2F815B0AB5>/V 5>>

This object is created by PoDoFo following the

void PdfEncryptSHABase::CreateEncryptionDictionary(PdfDictionary& dictionary) const

and is used to create later:

24 1 obj
<</Type/XRef/Encrypt 6 1 R/Filter/FlateDecode/ID[<CC5 [...]

Why is the 6 1 obj created?
How does pdfbox use the 23 0 obj directly?

A few info extracted with podofo:

void PdfParserObject::checkReference(PdfTokenizer& tokenizer)

DEBUG: The PDF file is encrypted
WARNING: Found object with reference 0 0 R different than reported 23 0 R in XRef sections

void PdfMemDocument::initFromParser(PdfParser& parser)

DEBUG: <</Type/XRef/Encrypt 23 0 R/Filter/FlateDecode/ID[<CC56D8A7F574DE7ED75787D94BF65288><CC56D8A7F574DE7ED75787D94BF65288>]/Index[ 2 18 21 4]/Info 2 0 R/Length 76/Root 21 0 R/Size 25/W[ 1 2 1]>>

Trying to open the signed file

PoDoFo encountered an error. Error: 7PdfErrorCode::InternalLogic	Error Description: An internal error occurred.	Callstack:	#0 Error Source : main/PdfParser.cpp: 97		Information: Unable to load objects from file
	#1 Error Source : main/PdfParserObject.cpp: 96		Information: Unable to parse the stream for object 22 0 R
	#2 Error Source : main/PdfEncrypt.cpp: 404		Information: Error AES-decryption data padding

I tried to see what the competitors are doing too. The closest to PoDoFo is MuPdf!
Here instead the pdfbox encryption module

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