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Re: updated WOFF specification

From: Jonathan Kew <jonathan@jfkew.plus.com>
Date: Thu, 10 Sep 2009 17:14:21 +0100
Cc: www-font <www-font@w3.org>
Message-Id: <C476AA30-3444-47B0-B7EB-554A9DB2E47E@jfkew.plus.com>
To: John Hudson <tiro@tiro.com>
On 10 Sep 2009, at 17:05, John Hudson wrote:

> A quick question re. WOFF:
>
> When a WOFF format font is created, what happens with the dsig in  
> the original OT font. Is this preserved in some way? Is the DSIG  
> table compressed in the same manner as the other tables, and does it  
> remain verifiable in some way?

It used to be that it was discarded (because the signature would no  
longer be valid), but the WOFF spec has now been tightened up such  
that if you encode a fully valid OpenType font (i.e., checksums are  
correct, tables properly padded, etc) and then decode it again, you  
get a binary-identical file back. And therefore the DSIG can be  
preserved and verified (by decompressing, and then proceeding as usual).

If the original font has inconsistencies such as a bad checksum, then  
the encoder will fix this (with a warning) and discard the DSIG (also  
with a warning) because the signature would no longer match the data.

Hope that clarifies it for you.

JK
Received on Thursday, 10 September 2009 16:15:09 GMT

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