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Re: [ietf-smtp] DKIM encryption, was Request for discussion

2013-10-19 16:43:51
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Presumably you are referring to using the destination domain DKIM keys to 
encrypt ...

Sort of.  Here's a straw man I sent to one of the MAAWG lists last
month:

Sender fetches TXT _encrypt._domainkey.recipient.com.  If it exists,
it uses the p= public key to encrypt the whole message, embeds it as a
MIME application/dkim-encrypted body in a new message to the original
address, and sends it off.

Recipient MTA receives message, and if it has an
application/dkim-encrypted body, decrypts and unwraps it and delivers
the original message.  Intermediate MTAs don't have to do anything
special.

Bonus anti-traffic analysis hack: new wrapped message is always sent
to: postmaster(_at_)recipient(_dot_)com with subject: encrypted message, real
recipient and subject recovered from Subject: and DKIM-Encrypted-To:
headers in the encapsulated message.

A single header field for the recipient(s) really doesn't cut it. There's lots
more to message envelopes these days. I suggest you take a look at RFC 2442
instead. Batch SMTP has a long and quite successful history of being used for
this sort of thing.

And now, I'm afraid, I'm going to have to do the IPR dance: I'm aware that
there may be intellectual property claims on this scheme. Unfortunately I
really cannot say more than that - not because of any sort of  confidentiality
restrictions, but rather because I don't know the details.

Specifically, I was contacted maybe 6 months ago by a law firm looking for
prior art on exactly this scheme. They didn't identify the patent and I didn't
ask for any details because I'm instructed by my employer to never do that.
But apparently there's one out there.

                                Ned


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