Sunday, November 7, 2010


You know the drill. You can get the new release here, and the changelog follows:

  • added a new "Font Obfuscation" context menu for font files in the Book Browser; the user can now select (or de-select) the use of Adobe's or the IDPF's font obfuscation methods; this also resolves the problem where Sigil refused to open epub files that use such obfuscated fonts with the message that the epub has DRM
  • fixed a validation issue caused by Sigil using "application/x-font-opentype" as the OPF mimetype instead of "application/"
  • fixed a crash when opening the TOC editor for some epub files (issue #654)

There are two reasons why you are seeing a new release so soon: the first one is an unfortunate bug that causes a crash when opening the TOC editor for certain epub files. While rare, it can still happen and frankly, it’s not rare enough. This needed to be fixed pronto.

The second reason is the recent introduction of the “this epub has DRM and cannot be opened” message for epubs that have an “encryption.xml” file in the META-INF folder. The message is valid since Sigil can’t open encrypted epub files (nothing can without the key, that’s the sad point of DRM), but unfortunately Adobe InDesign obfuscates embedded font files. This, naturally, creates an entry in the “encryption.xml” and now Sigil refuses to open your epub. And the only thing you did was tell InDesign to embed a font.

As far as I know, it’s not possible to tell InDesign not to obfuscate embedded fonts. It does this by default. The sad thing is that most people don’t know this is happening; they just embed the fonts and since they appear to work fine when the epub is opened with ADE, they call it a day. Personally, I have a problem with this: if Adobe wants to placate the font foundries with some patently absurd font mangling scheme, fine. But give the user a choice of turning this crap off. Or at the very least tell them it’s happening. If I were Adobe, I’d spend less time thinking up such nonsense and more time improving their epub export option since it’s currently… somewhat unusable[1].

Don’t get me wrong, I know perfectly well why they want fonts obfuscated: licensing issues. Most font licenses don’t allow embedding a font in a way that the font itself can be easily extracted from the distributed file. Font obfuscation is thought to solve this.

It doesn’t.

De-obfuscating a font mangled in such a way is laughably trivial; a twelve-year-old could write a program in 10 minutes that de-obfuscates the font files. The same thing goes for the IDPF’s method. It doesn’t prevent anyone from doing anything. While I find the whole thing ridiculous, I understand some want to give themselves at least an illusion of legal justification. All I’m saying is that Adobe shouldn’t be forcing people who know better into using something so silly.

Little do the users of InDesign know that this scheme makes their epub files invalid and that such fonts will only work in Reading Systems that support this. It works in ADE since Adobe naturally made sure that their RS supports their font obfuscation method. While I personally think that font obfuscation is utterly pointless, lots of Sigil’s users have epubs coming from InDesign… So Sigil has to cave.

You will notice that there is now a new right-click context menu entry for font files in the Book Browser. Under the “Font Obfuscation” sub-menu, you will see two actions: “Use Adobe’s Method” and “Use IDPF’s Method”. These select which font obfuscation method to use on the font files.

By default, the state in which the font file was found when the epub was opened is preserved when saving; so if you open an epub file with InDesign-embedded fonts, you will see a check-mark next to  “Use Adobe’s Method” in the  “Font Obfuscation” sub-menu. This means that the obfuscation is in place and will be preserved after a save. You can also click on “Use Adobe’s Method” to remove the check-mark, thus un-obfuscating the font file (I highly recommend this). Same thing goes for  “Use IDPF’s Method”; clicking on a checked method unchecks it and removes the obfuscation.

Since Sigil now supports font obfuscation (and de-obfuscation), you will not see that “cannot open because of DRM” message for epubs that use such fonts.

Don’t forget that InDesign still[2] flat-out refuses to to list the embedded fonts in the OPF file, even though the specs say it has to. That means the fonts won’t be picked up when the epub is opened in Sigil. I’ll probably add yet another InDesign workaround down the line to handle this.


[1] That’s the most restraint I’ve shown in a year.

[2] As of CS5. I just checked.