[ietf-dkim] Interesting Dupe Signatures

[John R. Levine]

>>    DKIM-Signature: .... c=relaxed/relaxed;   // dupe
>>    DKIM-Signature: .... c=relaxed/relaxed;   // dupe
>>    DKIM-Signature: .... c=relaxed/relaxed;   // dupe
>>    DKIM-Signature: .... c=simple/relaxed;    // other signer
>>    DKIM-Signature: .... c=relaxed/relaxed;   // other signer
>
> You need two header and one body canonicalizations in that example.  And that presumes there's no "l=", which creates another dimension in the matrix of canonicalizations you need to run.

I don't see much benefit for saving the header hash, since it depends on 
the order that the headers are listed in the h= header.

On the other hand, doing both the simple and relaxed body hashes in a pass 
over the body would handle about 99.999% of the signatures that anyone 
cares about.  I haven't seen many l= signatures, other than from Cisco, 
and I don't think I've seen any where the l= didn't cover the whole 
message.

R's,
John