[mpeg-OTspec] Proposed update of the 'head' table flags

[Bob Hallissy]

On 2014-04-30 at 16:23 Levantovsky, Vladimir wrote:
> WebFonts WG believes that WOFF2 compliant encoders should also set 
> this flag to indicate the fact that a font file was subjected to the 
> lossless transform (which is similar but not identical to the original 
> MTX) and suggests to modify the bit 11 description as follows:
>
> “Bit 11: Font data is ‘lossless’ as a results of having been subjected 
> to optimizing transformation and/or compression (such as e.g. 
> compression mechanisms defined by ISO/IEC 14496-18, MicroType Express, 
> WOFF 2.0 or similar) where the original font functionality and 
> features are retained but the binary compatibility between input and 
> output font files is not guaranteed. As a result of the applied 
> transform, the ‘DSIG’ Table may also be invalidated.”
>
> I believe this new definition preserves the original intent of this 
> flag and extends use cases when this flag setting may be a benefit. It 
> will also provide an indication that certain transforms may cause 
> Digital Signature table data be invalidated as a result.
>
>

I'm not an expert on digital signatures, but isn't it the case that by 
changing bit 11 from 0 to 1 (to indicate the lossless transform) the 
DSIG *will* be invalidated?

In any case (and I suppose this is really a question for the WebFonts 
WG) what is a client supposed to believe about a font if it arrives with 
Bit 11 set and a signature that doesn't validate?

Bob
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