Thank you for the clarification, I actually skipped reading a part of your question. Actually version /V key 5 is supported but it's not supported /R 6 as you found out. I have a (paid) official copy of ISO 32000-2:2017 (not very latest 2020), and about /R it says:
R, number: A number specifying which revision of the standard security handler shall be used to interpret this dictionary: [...] 5 (PDF 2.0; deprecated) Shall not be used. This value was used by a deprecated proprietary Adobe extension. 6 (PDF 2.0) if the document is encrypted with a V value of 5. It seems PoDoFo supports revision /R 5 as part of supporting this deprecated Adobe extension. The question now is how much different it is this /6 from /R 5 (there are certainly differences). If anybody is going to implement it I recommend only to do it with the very latest non-draft version of the standard since I can see the exact algorithm being changed between drafts and final version, even in 2017 version. Unfortunately ISO now holds the copyright for the newer versions of the PDF standard and it's not a freely downloadable standard anymore :( . On Fri, 29 Oct 2021 at 17:32, F.E. <exler7...@gmail.com> wrote: > Yes, Podofo supports the pdf 1.7 version of AES256 (-> extension level 3), > when libidn is available. We use this already. > > But an AES256 encryption with 'Version 5' should refer to pdf 2.0 (or pdf > 1.7 extension level 8). It's essentially a new, more secure AES256 > encryption implementation. Podofo does not support that as of now. > Am 29.10.2021 um 13:35 schrieb Francesco Pretto: > > Support should already be present in PoDoFo but you must add support for > Libidn[1]. As far as I remember only Libidn 1.x is supported in PoDoFo > because Libidn 2.x is API incompatible. > > [1] https://www.gnu.org/software/libidn/ > > On Fri, 29 Oct 2021 at 13:24, F. E. <exler7...@gmail.com> wrote: > >> Hello dear podofo users, >> >> I have a password protected pdf file (Pwd: test), which podofo fails to >> load: >> >> ePdfError_UnsupportedFilter: Unable to load objects from file.: Error while >> loading object 8 0 >> >> Unsupported encryption method Version=5 Revision=6 >> >> I checked in the pdf reference 1.7, and there was indeed no Version 5 or >> Revision 6 listed. >> >> After some more digging I found out, that the pdf should follow the pdf 2.0 >> standard (iso 32000-2), >> which features a more secure AES 256 encryption. >> >> My question now is, is anyone familiar with this kind of encryption, >> and would it be theoretically possible to add it to podofo (if anyone had >> the time for it ...) ? >> >> Greetiings, >> >> F.E. >> >> >> _______________________________________________ >> Podofo-users mailing list >> Podofo-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/podofo-users >> >
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