Stefan,
> On outgoing mails, I noticed that the DKIM headers inserted by
> amavisd-new look like that:
>
> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=incertum.net; h=
> user-agent:in-reply-to:content-transfer-encoding
> :content-disposition:content-type:content-type:mime-version
> :references:message-id:subject:subject:from:from:date:date
> :received:received:received; s=2007; t=1271446098; bh=DmklXs6cV2
> 9nE5nZkyU6E1NrclzUZQG5M3cYwm9c1rc=; b=jKiW55408hyTqQXHQiQz25VtM1
> quWuFFyo1mrhiLKWkAjwfZkNr8ON0kNiT1ZVO/zWXoPR4DJHuKMBSTrU9cwBPFb+
> KJednFiMuToYRmHhxaOZNh2nwHFYRI2tEgLnZoiZM4aG4pMXaw+xxVyA5qITRvjw
> wxqjVqNQt96Zlqylg=
>
> As you might notice, "subject", "from" and "date" appear twice. Is
> that normal? Something to worry about? My DKIM related settings are
> pretty basic: [...]
> This happens with amavisd-new 2.6.4 and Mail::DKIM 0.32.
Yes, it is normal, and it is intentional.
amavisd-new-2.6.4 release notes :
- support inclusion of null header field names in an 'h' tag of a DKIM
signature generated by amavisd for specified header field names, thus
preventing third parties from prepending additional occurrences of
these header fields without breaking a signature; useful for example
for protecting a recipient's mail reader or a filter from being tricked
by supplying a duplicate From or Subject header fields; the protection is
requested by specifying a value larger than 1 in %signed_header_fields,
e.g.:
$signed_header_fields{'from'} = 2;
$signed_header_fields{'subject'} = 2;
$signed_header_fields{'message-id'} = 2;
$signed_header_fields{'content-type'} = 2;
Please restrict values used in %signed_header_fields to 0, 1, or 2,
consider other values reserved for future use.
By default the following header fields are protected from duplicates by
a DKIM signature generated by amavisd: From, Date, Subject, Content-Type.
To revert to a classical behaviour, set their value in %signed_header_fields
to 1, e.g.:
$signed_header_fields{lc($_)} = 1 for qw(From Date Subject Content-Type);
See also RFC 4871 for explanation of the 'h' tag semantics.
Mark
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