Adobe DE "decrypts" fonts with XOR

llasram · 12-05-2008, 07:23 PM

I noticed Adobe had some new documents up on the "Digital Publishing Technology" section of their website, including the intriguingly-named "Protecting Embedded Fonts in EPUB Documents." It does in fact describe what the title suggests -- how the EPUB files produced by InDesign "encrypt" embedded fonts and how Adobe DE reads them back. And yep, the method is XOR -- just XOR the first 1024 bytes of the font-files with the big-endian form of the first "urn:uuid:" <dc:identifier/> in the OPF metadata.

I'm trying to decide what I think of this. It isn't going to prevent a single EPUB reading application author from being able to load embedded fonts, but it probably will stop people from just casually yanking copyrighted OpenType fonts out of random e-books. I think it may actually be quite clever of them.

kovidgoyal · 12-05-2008, 07:44 PM

Sigh adding more layers of complexity just to keep the lawyers happy.

EDIT: Though I have to say that if they succeed in redefining copyright as "The prevention of casual copying", I will be thrilled.

12-05-2008, 07:23 PM	#1
llasram Reticulator of Tharn Posts: 618 Karma: 400000 Join Date: Jan 2007 Location: EST Device: Sony PRS-505	Adobe DE "decrypts" fonts with XOR I noticed Adobe had some new documents up on the "Digital Publishing Technology" section of their website, including the intriguingly-named "Protecting Embedded Fonts in EPUB Documents." It does in fact describe what the title suggests -- how the EPUB files produced by InDesign "encrypt" embedded fonts and how Adobe DE reads them back. And yep, the method is XOR -- just XOR the first 1024 bytes of the font-files with the big-endian form of the first "urn:uuid:" <dc:identifier/> in the OPF metadata. I'm trying to decide what I think of this. It isn't going to prevent a single EPUB reading application author from being able to load embedded fonts, but it probably will stop people from just casually yanking copyrighted OpenType fonts out of random e-books. I think it may actually be quite clever of them.

12-05-2008, 07:44 PM	#2
kovidgoyal creator of calibre Posts: 45,604 Karma: 28548974 Join Date: Oct 2006 Location: Mumbai, India Device: Various	Sigh adding more layers of complexity just to keep the lawyers happy. EDIT: Though I have to say that if they succeed in redefining copyright as "The prevention of casual copying", I will be thrilled. Last edited by kovidgoyal; 12-05-2008 at 08:06 PM.

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