Oh, and the tool currently mis-calculates hashes of TTC's older than about 15 years. I only have 4 such font files. The issue is well-understood, just haven't got round to it. A TODO.

The 4 YuGoth* TTC fonts on windows 10 also gets their hashes mis-calculated. It is the same issue with my mis-calculation of very old TTCs. The issue is well-understood, just haven't got time to work on it. I probably should throw an error, rather than let it continue to mis-calculate meanwhile.

probably warn, rather than error, since bad hashes don't necessarily mean bad internal data for validation purposes: a table with length X and a bad hash might still have perfectly valud data that exactly fills the table's indicated length, so that while there is a bad hash, the fault was in the font's generator, not the font's table data.

No, a bad hash is a bad hash - it means that the font was modified after signing - even for very legitimate tasks like adding glyphs, etc, which are perfectly valid fonts. The correct way to deal with this is to re-sign the font after modifying it.

As for whether this is an error or warning, you should file this with upstream and let the Microsoft folk decide. They put it as error, so it is up to them to change it.

fair enough

The digital signature is for the author to certify "this is exactly how I release it". There are many good reasons for others to modify the font without consulting the original author, and even release a new version - where the license allows - but the new version should be re-signed by the modifying person. DSIG is about authenticity of who-owns-it, not correctness of font structures.

yeah, forgot this was DSIG-exclusive behaviour for a moment.

Just note to myself: the TTC issue with very old TTC's and the 4 YuGoth* TTC fonts is that the current get_TTC_digest() ( line 539 to 638 -ish in https://github.com/HinTak/Font-Validator/blob/master/DSIGInfo/DSIGInfo.cs as of now) can only cope with either directory-contiguous or member-font-contiguous TTC's.

i.e. it can only cope with the ttc layout directory1-directory2-directory3...directoryN -font1-font2-font3...fontN or directory1-font1-directory2-font2...directoryN-fontN . Those exceptions don't belong to either - they have tables between member fonts interlaced.

Essentially all TTC in the last 15 years are in either category, or in any case, those I have.

v2.1 will say it cannot cope with very old TTCs and the 4 YuGoth TTC fonts, insead of saying the hash does not match. It is currently a bit ugly - throwing an UnImplemented Exception. I'll see if I can make it a bit better