Re: [PATCH] Unzip fails without optional extended local header signature

[Michael Gray]

On Wed, Nov 30, 2011 at 12:28 PM, Michael Gray <address@hidden> wrote:
> I just emailed Mark again, inquiring if he knows of any other software that 
> makes this choice.

Here is his reply:

Michael,

On Nov 30, 2011, at 2:17 AM, Michael Gray wrote:
> Can you point me to any other software in current use that *does not* emit 
> the signature before the data descriptor?

No, I have not tried to find such software.

The PKWare appnotes from 2001 through early 2006 show the data
descriptor field without the signature.  The appnotes from late 2006
through the latest appnote (in 2007) also show the data descriptor
without the signature, but mention in the comments that there may be a
signature.  If one strictly follows the format description in the
latest PKWare appnote (in fact in all of the PKWare appnotes), then
the data descriptor should have no signature.

One of the PKWare appnotes that does not discuss the signature at all,
6.2.0 (from 2004), is noted as the standard for Open Office XML
(ECMA-376 and ISO/IEC 29500).

The PKWare appnotes that do mention the signature state that
conforming decoders have to handle both cases:



"Although not originally assigned a signature, the value 0x08074b50
has commonly been adopted as a signature value for the data descriptor
record.  Implementers should be aware that ZIP files may be
encountered with or without this signature marking data descriptors
and should account for either case when reading ZIP files to ensure
compatibility."

Mark