rfc822-parse doesn't correctly unpack headers

I diagnosed the problem.

This is the message emitted by the Sender end (bracketed by <BEGIN> <END>):

<BEGIN>
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
d=good.emailtest.had-pilot.biz;
  <email address hidden>; q=dns/txt; s=mailkey; t=1340661225;
  h=Date : From : To : Cc : Subject : Message-ID : MIME-Version :
  Content-Type : Content-Disposition : User-Agent;
  bh=2cilj9JgD3aYI49HQfXVKgyfMmRb1qUViiejVxoJG2w=;
  b=RmjJNiUcdVSsppai2DBpof3/L6GpqEpuPDVxJL4jyCgQKtclWYIs+5p/ZaEHDOfgW+rg9Q
  R1CRsp6AU5gQoHP9ICViZ+TUUHsErG6F1Hi8EJzHnfxrkDm41FNtI1KuU7Q9VWhbTkVKTrgX
  zMhFjrVRjKS7EFE+B3YFbS9LpwFfA=
Received: (from night@localhost)
     by had1.antd.nist.gov (8.14.4/8.14.4/Submit) id q5PLriME003627;
     Mon, 25 Jun 2012 17:53:44 -0400
Date: Mon, 25 Jun 2012 17:53:44 -0400
From: Fushimi Inari <email address hidden>
To: <email address hidden>
Cc: <email address hidden>
Subject: Short01 test
Message-ID: <email address hidden>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.5.20 (2009-12-10)

all.
<END>

- I am using Sendmail 8.14.4 at the Sender (good.emailtest) and receiver
(pythentic) ends, and dkimpy 0.5.2 in the milters.
- There is a Sender ppymilter, that calculates the signature and
introduces the DKIM-Signature header at index 0,
and a Receiver ppymilter that does SPF and then verifies the DKIM signature.
- The signature is folded at the Sender end using dkim.fold(). This
splits the signature with "\r\n<space>" sequences.
- The message as delivered through Sendmail has newlines stripped.
Specifically, the "\r\n\" sequences in the DKIM-Signature are replaced
by "\r<space> ".
- This signature fails dkim.verify.
- When I explicitly replace the "\r<space>" sequences in the signature
with "\r\n" sequences, before giving the message to verify, the
signature verifies.

So I suspect there is a problem with the way that the
rfc822_parse(message) function 'unfolds' the signature.
Application of the 'lines = re.split(b"\r?\n", message)' statement would
seem to leave a set of spurious spaces in the signature. The lines
[i][0] in (<tab>, <space> ...) statement doesn't seem to patch it.
dkim.util.parse_tag_value already assumes the signature is correctly
unfolded when it isn't, and the computation fails.

I suspect the problem can be solved by fixing the way that rfc822_parse
unfolds the signature. Or by fixing the newline stripping behavior of
Sendmail. Or there's something even more arcane going on that I don't
yet know.

Regards,

Stephen.

On 6/19/2012 4:51 PM, Stuart Gathman wrote:
> Your question #200918 on dkimpy changed:
> https://answers.launchpad.net/dkimpy/+question/200918
>
> Stuart Gathman posted a new comment:
> If the bodyhashes in the DKIM-Signature header field are the same, then
> it is not a header hashing issue. The bh= includes both header and body
> hash. You didn't provide any details, e.g. the DKIM-Signature header
> field in question, or the exception. Note that calling the class method
> lets you get an informative exception, and not just a boolean result. I
> suspect that there is something wrong with the DNS record you published.
> There are many tests of sign/verify symmetry in the unit tests. If it
> turns out you have an actual failure, we'll add it to the suite.
>