that discrepancy between spec & implementation of DSIG hashing (RE: First draft of the ballot comments on the new amendment)

Hin-Tak Leung htl10 at
Sun May 22 11:09:50 CEST 2016

Hi Greg, and the other Microsoft folks,

I understand there are a few big typography events lately so this may have fallen through the crack. It has been almost a month - have you had any chance/time looking at the Microsoft implementation of the signing tool to confirm that it does not zero the checksum in the head table before hashing, in contrast to what it says in the spec?


On Wed, 27/4/16, Hin-Tak Leung <htl10 at> 

 Hi Greg,
 If you can have a look at the Microsoft code and check soon,
 that would be great. My implementation (

 ) was checked against at least all the Win 8.1 and win 7
 shipped fonts, so I am fairly sure that's how Microsoft
 signs their own shipping fonts :-). The checksum's are
 adjusted to those without the DSIG table, but not zero'ed. 
 Martin: If you can locate you old work, conceptually, the
 hash is simply of "a valid font stripped of the DSIG table +
 two bytes appended".
 On Wed, 27/4/16, Greg Hitchcock <gregh at>
  I've not had a chance
  to look at the code to verify this one way or another. It
  seems to me it would be wrong to not zero out the
  CheckSumAdjustment in the head table. I will not be able
  look at this right away, but hope to soon.

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