Re: FontForge encryption

On Sun 2014-11-09 12:45:33 -0500, Daniel Kahn Gillmor wrote:
> On Sat 2014-11-08 03:53:04 -1000, Jose David Bravo A wrote:
>
>> I have a font (woff) and I want to edit that font to change the mapping. 
>>
>> Ie, the letter A match the bitmap of the letter B, letter B match the bitmap of the letter C, etc. 
>>
>> With that, the only way to read a document will be having the font. Is possible to do that with font-forge using command line? 
>
> I note that your subject line is "FontForge encryption".
>
> The mechanism you describe is effectively what's known as a "caesar
> cipher" -- while it is arguably a form (an ancient form) of encryption,
> it is known to be trivially vulnerable to many forms of cryptanalysis.
> That is, a modern cryptographer would not consider this to be effective
> encryption at all.
>
> I recommend against calling this "encryption" at all so that you avoid
> giving people who might stumble across this neat trick the wrong idea
> about the security or safety of the process against even an
> marginally-competent adversary.

I wanted to follow up here to ask how this project is going.

Jose, despite my critique of the subject line (i still would avoid
characterizing the project as "encryption"), i do want to encourage you
to try things out and to hack on fontforge, and to share your results
with other people who  might have similar interests.

I suspect the transformation you're likely to want to do is doable from
the python interface, but i don't know fontforge's python bindings well
enough to be able to give you specific pointers.  Maybe someone else
here can give you more specific details?

I'd start with:

 import fontforge
 f = fontforge.load('myfont.woff')

and then the thing you want to explore is f and f.glyphs().  you might
experiment with f.replaceWithReference() or f.createChar().

When you've made some changes, you could try f.save().

hth,

        --dkg

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