>
> If you know the password, then there is no need to create a new PDF (at
> least in general, not sure of PoDoFo specifics here) – you can just sign
> the encrypted PDF directly *(ensuring that all the new objects are
> properly encrypted as well). *
>
That's the hard part, isn't it? At least it's not working with Podofo when
I'm doing that straightforward. See case 2.) of my first mail:
2.) Ok, so I changed my signing implementation to not use normal Write(),
> so I don't have to use update mode for loading. When I'm now loading the
> encrypted pdf document, it works and I'm able to place my signature. BUT,
> when I'm opening the file in a pdf viewer, it doesn't ask me for any
> password! I can see that my configured permissions are still there, so this
> part of the security settings is still there, but the password (user/owner)
> got lost.
>
2017-08-04 17:01 GMT+02:00 Leonard Rosenthol <lrose...@adobe.com>:
> If you know the password, then there is no need to create a new PDF (at
> least in general, not sure of PoDoFo specifics here) – you can just sign
> the encrypted PDF directly (ensuring that all the new objects are properly
> encrypted as well).
>
>
>
> Leonard
>
>
>
> *From: *"F. E." <exler7...@gmail.com>
> *Date: *Friday, August 4, 2017 at 9:57 AM
> *To: *Leonard Rosenthol <lrose...@adobe.com>
> *Cc: *"podofo-users@lists.sourceforge.net" <podofo-users@lists.
> sourceforge.net>
>
> *Subject: *Re: [Podofo-users] Signing encrypted pdfs
>
>
>
> >> would it work to append the pages of the encrypted pdf to an empty pdf
>
> >>
>
> > No, because you have to be able to decrypt the pages to combine them.
>
> I should've make clear that I'm assuming I can decrypt it xD.
>
>
>
> So yes, if I don't know the password, I can only add the encrypted pdf as
> an attachment to a new pdf and sign this.
>
> If I know the password, i thought I could use podofo to load the encrypted
> pdf, append its pages to a new empty pdf and sign it afterwards.
>
> Is this wishful thinking or could it work :) ?
>
>
>
> 2017-08-02 15:46 GMT+02:00 Leonard Rosenthol <lrose...@adobe.com>:
>
> > would it work to append the pages of the encrypted pdf to an empty pdf
>
> >
>
> No, because you have to be able to decrypt the pages to combine them.
>
>
>
> (in the FWIW/historical category – there are remnants of attempts to solve
> this still present in the PDF standard, in the form of Crypt Filters, but
> it turns out to just be a problem not worth solving in the long term)
>
>
>
> Leonard
>
>
>
> *From: *"F. E." <exler7...@gmail.com>
> *Date: *Wednesday, August 2, 2017 at 5:53 AM
> *To: *"podofo-users@lists.sourceforge.net" <podofo-users@lists.
> sourceforge.net>
> *Subject: *Re: [Podofo-users] Signing encrypted pdfs
>
>
>
> > Hi,
> > load for update (and using WriteUpdate()) means that you keep the file
> > as is and only add your changes at the end. Having new values
> encrypted
> > and old values not, or using different encryption method, or even
> > trying to use old encryption on the new content, doesn't sound right
> to
> > me.
>
> Ok, that explains my 1.) and the side note.
>
> > It’s not technically possible to sign an encrypted PDF – because there
> is no way to encrypt the new update section
> > with the same key as the previous sections – unless you know what it is
> (and then it’s a bit tricky still).
>
> Convinced me ^^.
>
>
>
> Some follow-up questions I'd like to ask:
>
> - For my case 2.), signing an encrypted pdf with normal loading, I
> learned that the resulting pdf seems to have no password at all.
> How does this happen? Does podofo remove the password encryption
> automatically when writing the signed file or is this some kind of error in
> the viewer?
> - Instead of adding the encrypted pdf as attachment, which is a nice
> idea I didn't think about, would it work to append the pages of the
> encrypted pdf to an empty pdf and set encryption and signature then? I know
> there's an issue with embedded files when appending, but I could extract
> the files and delete them prior to appending and add them later again.
> - I had a third question, but I don't know what it was about anymore
> :-/.
>
>
>
> Regards,
> F.E.
>
>
>
>
>
> 2017-08-02 0:45 GMT+02:00 Leonard Rosenthol via Podofo-users <
> podofo-users@lists.sourceforge.net>:
>
> It’s not technically possible to sign an encrypted PDF – because there is
> no way to encrypt the new update section with the same key as the previous
> sections – unless you know what it is (and then it’s a bit tricky still).
>
> Better to simply create a new PDF with the encrypted PDF as an attachment
> as part of a collection and then sign the new PDF.
>
> Leonard
>
> On 8/1/17, 11:27 AM, "zyx" <z...@litepdf.cz> wrote:
>
> On Tue, 2017-08-01 at 16:38 +0200, F. E. wrote:
> > As a side note, I noticed that I cannot use load-for-update in this
> > case, because the resulting pdf has an unknown password protection.
> > Neither my specified user nor owner password work for decryption.
> > That's odd and mighht be a bug, don't know ...
>
> Hi,
> load for update (and using WriteUpdate()) means that you keep the file
> as is and only add your changes at the end. Having new values encrypted
> and old values not, or using different encryption method, or even
> trying to use old encryption on the new content, doesn't sound right to
> me.
>
> Doing sign & encrypt at the same time sounds the way to go, as you
> figured out yourself.
> Bye,
> zyx
>
> --
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