Re: Merging CSS Shaders proposal into Filter Effects

On 31/10/2011, at 4:34 PM, Tab Atkins Jr. wrote:

> On Mon, Oct 31, 2011 at 10:30 AM, Vincent Hardy <vhardy@adobe.com> wrote:
>> Tab: you mention that more things than the shading language are contentious.
>> Can you explain what these contentious issues are?
>> Are you referring to the issues raised on the mailing list:
>> http://www.w3.org/Graphics/fx/wiki/Custom_Filters#Issues_List
>> or something else?
> 
> I'm specifically referring to the issue of selecting through a vertex
> filter, and the security issues with using a fragment shader to
> extract information through a timing channel.  Both of these are
> unaddressed and probably difficult to deal with, and may take a decent
> amount of time to deal with.

I don't think either of these are limited to shaders. Regular XML/SVG filters have the same issues: A displacement map can significantly move content making selection confusing, and a filter can be written to theoretically run faster/slower depending on the input (component transfer, for example).

Regarding the timing attack in particular, CSS filters have the benefit that it's much harder to measure the effect. Unlike <canvas>, you don't really control the drawing operation. You can't be sure that the element you're attacking was the only thing rendered. That doesn't mean the attack is impossible.

Dean

> 
> 
>> The CSS shaders proposal responds to the feCustom 'question' in the 'Filter
>> Effects' specification and it seems more natural to integrate it than keep
>> it a separate specification.
> 
> Or we can just move the definition of <feCustom> to Shaders.
> 
> ~TJ
>