[GSoC2012] Introduction / Signed PDF export

[Thorsten Behrens]

Hi Gökçen,

let me chime in here - so barring any technical issues, or further
insight, I'd love to have this result in something that can be used
under European e-government regulations.

Something to look into for guidance clearly is PortableSigner, which
is maintained by the Austrian government AFAIK - with that:

> * The signing method: What kind of signature handler we may use?
> ByteRange method is sufficient and for the SubFilter value of the
> signature dictionary, adbe.x509.rsa.sha is OK, right? In this case, Cert
> entry of the Signature dictionary will contain X.509 certificate chain
> and Contents key wil contain the byte range digest.
> 
Yeah, filter something like PPKLite, subfilter adbe.pkcs7.sha1 or
adbe.pkcs7.detached - ByteRange makes total sense, and so does
X.509 certs - I'd be content if you can use PKCS#12 ones e.g. :)

> * Is the MDP (modification detection and prevention) required? This is
> used for object signatures, right? But the byte-range based document
> signatures is more suitable. I think I must also investigate the status
> of the digital signature verification in Linux PDF readers and maybe
> poppler, so the users must be able to verify the signed PDF files :)
> 
Right, not much insight into that - but I would suggest that,
everything else being equal, do what signature laws require.

> * Which PDF version should be preferred? As far as I can see, SHA256
> digestion is introduced in PDF 1.6, so the decision of digest method may
> effect the minimum PDF version to be used, right?
> 
1.5 should hopefully be enough.

Random links:

http://portablesigner.sourceforge.net/
http://en.wikipedia.org/wiki/EGovernment_in_Europe
https://www.bsi.bund.de/cae/servlet/contentblob/487196/publicationFile/31102/esig_pdf.pdf

HTH,

-- Thorsten
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