[MPEG-OTSPEC] DSIG spec issue

[Dan Rhatigan]

We decided a few years back to stop signing the Adobe Originals, and including a stub DSIG table just in case any implementations try to verify presence of the table. Also, at the time no one was able to confirm any scenarios that still required a valid signature. We’ve still not seen problems have come up about the lack of actual signature, so I’m in favor of deprecating the use of DSIG altogether.


—Dan



From: mpeg-otspec <mpeg-otspec-bounces at lists.aau.at> on behalf of "Levantovsky, Vladimir" <Vladimir.Levantovsky at monotype.com>
Date: Wednesday, August 26, 2020 at 12:10 PM
To: Peter Constable <pgcon6 at msn.com>, Bobby de Vos <bobby_devos at sil.org>, Dave Crossland <dcrossland at google.com>, mpeg-otspec <mpeg-otspec at lists.aau.at>
Subject: Re: [MPEG-OTSPEC] DSIG spec issue

FWIW, the stripping of DISG is also a necessity for WOFF2. Due to transforms and data pre-processing / optimization steps applied as part of the WOFF2 encoding steps [that invalidate the DSIG], it is required that “the compliant WOFF2 encoder MUST remove the DSIG table from an input font data, prior to applying transformations and entropy coding steps.” (https://www.w3.org/TR/WOFF2/#table_format<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.w3.org%2FTR%2FWOFF2%2F%23table_format&data=02%7C01%7Crhatigan%40adobe.com%7Cd4c8c759bb5d437d061608d849da8d37%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637340550313046438&sdata=NE7FenY%2FYkWNo%2BI6c7FbI0RnnTFMfcjLp1TEQtijxhU%3D&reserved=0>)

I’d say let’s deprecate DSIG once and for all.

Vlad


From: mpeg-otspec <mpeg-otspec-bounces at lists.aau.at> On Behalf Of Peter Constable
Sent: Wednesday, August 26, 2020 9:53 AM
To: Bobby de Vos <bobby_devos at sil.org>; Dave Crossland <dcrossland at google.com>; mpeg-otspec <mpeg-otspec at lists.aau.at>
Subject: Re: [MPEG-OTSPEC] DSIG spec issue

Office has a font service, serving fonts to (recent versions of) Office apps. My understanding is that they strip DSIG tables from fonts in the service. So, I would assume that recent versions of Office shouldn’t require DSIG tables to enable features in Latin fonts, though I haven’t confirmed that.

This is all product commentary: it can inform whether DSIG may still be relevant for fonts, though of course doesn’t belong in the spec itself.


Peter

From: Bobby de Vos <bobby_devos at sil.org<mailto:bobby_devos at sil.org>>
Sent: Wednesday, August 26, 2020 6:01 AM
To: Peter Constable <pgcon6 at msn.com<mailto:pgcon6 at msn.com>>; Dave Crossland <dcrossland at google.com<mailto:dcrossland at google.com>>; mpeg-otspec <mpeg-otspec at lists.aau.at<mailto:mpeg-otspec at lists.aau.at>>
Subject: Re: [MPEG-OTSPEC] DSIG spec issue


In addition to triggering the OpenType icon, a DSIG was (is?) needed in older versions of Microsoft Word to process some OpenType features in Latin script fonts.

https://github.com/googlefonts/fontbakery/issues/1845#issuecomment-564383952<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fprotect-us.mimecast.com%2Fs%2FWqy2CwpA5KsGM0Z7IqyVTq&data=02%7C01%7Crhatigan%40adobe.com%7Cd4c8c759bb5d437d061608d849da8d37%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C637340550313046438&sdata=lRJ3IlQjgv%2BwvsEBro01TESGyLwyjRor3TK80G3lFsU%3D&reserved=0>

As recently as Office 2013 this was the case, and Office 2013 has not reached end of life yet.
On 2020-08-25 8:01 p.m., Peter Constable wrote:
I think at one time, yes, but I don’t think that’s been relevant since Windows 7.


Peter

From: mpeg-otspec <mpeg-otspec-bounces at lists.aau.at><mailto:mpeg-otspec-bounces at lists.aau.at> On Behalf Of Dave Crossland
Sent: Tuesday, August 25, 2020 6:09 PM
To: mpeg-otspec <mpeg-otspec at lists.aau.at><mailto:mpeg-otspec at lists.aau.at>
Subject: Re: [MPEG-OTSPEC] DSIG spec issue

Wasn't there something about needing a DSIG table to trigger the OpenType icon in Windows Explorer?

--
Bobby de Vos
bobby_devos at sil.org<mailto:bobby_devos at sil.org>
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