Generate encrypted pdfs about pdf-writer HOT 3 CLOSED

Cant. Hummus does not read or write encrypted files

from pdf-writer.

That is what I seen from sources. I meant any pointers in how to extend it to support it.

I started read up pdf documentation on encryption (even found small round up of it https://www.cs.cmu.edu/~dst/Adobe/Gallery/anon21jul01-pdf-encryption.txt )

It seem only thing needed is adding encrypt dictionary plus encrypting all streams while writing them.
Assuming I manage to create this encrypt dictionary get encryption algo right.
And I guess it wouldn't be that hard to pass all stream writes to de/encryption function before reading/writing them?

I still need to read up on encryption part of pdf and than to figure out how easy would it be to add it to PDF-Writter.

So far I only need writing encrypted pdfs and I'll have either to hack in encryption in or look up another library. So I hopped for some input to make hacking it in easier :)

Greetings

from pdf-writer.

As far as my understanding goes encrypting encrypts all strings and streams.

For writing, you should look into ObjectsContext.h which takes care of writing the basic PDF elements.
For instance, implementing encryption when writing strings can be done by modifying the string writing methods of this class.
For streams writing just implement the encryption through a new IByteWriterWithPosition that does encryption and add it in the PDFStream constructor. i do that already for flate, so adding something similar for encryption should work well (just figure out which goes on top of which :) and also do this for unfiltered streams).

adding the relevant dictionaries should be done on the catalog and you can look into DocumentContext class to see where the catalog is written in endpdf.

For reading it's kind of simpler cause all goes through PDFParser. check where strings are being read and add also relevant code for the stream reading helper. seems like i did have something in mind for reading encrypted files, because i have this mParserExtender member in the parser which is an optional extender that you can add to implement the relevant reading helpers in case a file is encrypted. i suggest you follow its methods.

hopefully this should cover all usages and provide you with a working implementation.

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