[pdftex] pdftex-pdfcrypt update

Ricardo Sanchez Carmenes carmenes at bioquimica.uniovi.es
Wed Mar 28 11:45:27 CEST 2001

On Wed, 28 Mar 2001, Hans Hagen wrote:

> At 07:13 PM 3/27/01 +0200, Ricardo Sanchez Carmenes wrote:
> > ... 
> >And leave to the user or the macros to take care of calculating the right
> >permission value ? Maybe a mixed solution could be useful.
> I'm not that familiar with the details, but does the permission play a role
> in the calculations? If so, then it should be keywords. For instance: can

Yes, they do.

> one change the /P entry in a pdf file without violating the file? 

Of course not. If would be like having a high security door, but leaving
the keys hanging from the door permanently.

> Just curious: how easily can a file be decrypted? 

Well, it's a question for experts, and I'm not, but apparently it is not
so difficult. I guess that as the encryption algorithm only uses a 5-byte
key, brute-force approaches are affordable.

I think there even is a company that can find lost passwords for a fee. I
wouldn't rely on this for higly sensible material. But the PDF specs
make it possible to include custom-made encryption algorithms (or
"encryption filters"), easy to do with pdftex with pdfcrypt. The only
trouble is that you would need custom-made pdf readers too. It would be
easy to modify xpdf accordingly, and I maybe it would possible to make
plug-ins for the acrobat reader too.

> >In short, your suggestions about syntax sound reasonable, but I still
> >would like to hear others. The current syntax works fine for me, and
> >I must recognize that coding the primitive was not the easiest part for me
> maybe thanh can help you with that part since he's a master in tex syntaxes
> now -) 


> >BTW, did you try it already ? You have pretty complicated pdf files that
> >make use of niceties that I do not realy use, and they would be a good
> >test.
> i'll have a look at it [normally work on windows, so i have to play around
> with the linux machine in such a way that it does not break other processes]
> Is it possible to post a djgpp cross compiled version? Thanh has a script
> for that. 

I'll ask him.

Regards, Ricardo.

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