[pdftex] pdftex-pdfcrypt update
Ricardo Sanchez Carmenes
carmenes at bioquimica.uniovi.es
Thu Mar 29 03:25:45 CEST 2001
On Wed, 28 Mar 2001, Hans Hagen wrote:
> At 10:45 AM 3/28/01 +0200, Ricardo Sanchez Carmenes wrote:
> >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.
> so part of the key is hardcoded in acrobat viewers, well then it's a matter
> of time before that key is public. Can you view your files with GS?
You can view the file with GS if you install the correct pdf_sec.ps file
where the decoding algorithm is contained, AND you provide manually the
correct owner or user password for that file.
The words "key is public" is missleading. Every encrypted document has its
own "unique" 5-byte key calculated from the passwords, the file ID and the
permits. There is no and there will not be any "universal" key that would
open every encrypted document. But using brute-force approaches you can
find the unknown key. A 5-byte key means that there are about 10^12
different keys, not so many for the CIA.
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