Re: [ietf-dkim] DKIM Scouts, was 8bit downgrades

John R. Levine wrote:
> > > It tells me signing and encryption certificates are valid and even their
> > > root certificates are valid...
> > Well, something's wrong with it.  I checked the signature in Alpine,
> > Thunderbird, and Evolution, and they all agree it's fine.
> I went back and looked in more detail.  The problem appears to be that 
> this mailing list wraps the signed body in a MIME multipart/mixed 
> section including both the signed message and the unsigned footer.  Some 
> MUAs look inside the mixed and see the signature, some don't.  For the 
> ones that do, I haven't checked to see how if at all they distinguish 
> the signed part from the unsigned when they show you the message (shades 
> of all the l= arguments.)
>
> So this tells me that existing mail software doesn't try very hard to 
> recover signatures from modified messages, even for simple changes that 
> don't need any guessing or heuristics to undo.  Why would anyone think 
> that the situation with DKIM would be any different?
I think you were telling people for a while now to use it for some reason.

Anyway, I don't think the problem is as you state.

 From what I see, I think the issue here is no MIME Application Type 
association for the application and extension your message was made. 
Your email provides this MIME info:

Content-Type: APPLICATION/pkcs7-signature; name=smime.p7s
Content-Transfer-Encoding: BASE64
Content-Description: S/MIME Cryptographic Signature
Content-Disposition: attachment; filename=smime.p7s

Software that offer auto launching (generally with user permission 
necessary) using MIME Application association, can either have its own 
table or depends on the OS to provide it.

For example, under Windows, you can use a console window using the 
ASSOC command to get the file type for the extension:

    ASSOC .p7s

and it returns

.p7s=P7SFile

then you use the FTYPE command to see what application is responsible 
to handle this file type.

    FTYPE P7SFile

and it returns:

p7sfile=rundll32.exe cryptext.dll,CryptExtOpenPKCS7 %1

So if the email has an attachment file name/extension smime.p7s,  then 
it should allow the user (with permission) to load it by running the 
above rundll32.exe process passing the rest of the line as parameters 
and substituting %1 with the local temp storage FQFN for smime.p7s

Now, under TBIRD, it apparently is independent of the built-in Windows 
MIME association table in the registry.  So one would think that 
Outlook would not have a problem and indeed it doesn't; it displays a 
"seal icon" save button for the SMIME.P7S attachment file when viewing 
the message under OE.

Under TBIRD, you can click

     TOOLS | OPTIONS

and under the Attachments properties tab, you will see the View & Edit 
Associations button.   For me, it is empty list - no MIME associations 
so shown as a file name "PART 1.2"

Now why didn't it atleast show SMIME.P7S as a file attachment?   You 
did have:

    Content-Disposition: attachment; filename=smime.p7s

You should check bugzilla or asks the TBIRD folks why it doesn't at 
least show the actual file name as the attachment because even if 
TBIRD doesn't have its own table, when the user tries to save it, 
Windows will most likely make the shell association.

BTW, under OE, while it does show the SMIME.P7S icon attachment, the 
message display is blank.  That may be related to what you are talking 
about.  In any case, its all fubar.

-- 
Hector Santos, CTO
http://www.santronics.com
http://santronics.blogspot.com


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