Re: [perpass] Another mail-related proposal

Jim Fenton <fenton@bluepopcorn.net> Tue, 20 August 2013 05:24 UTC

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Date: Mon, 19 Aug 2013 22:24:01 -0700
From: Jim Fenton <fenton@bluepopcorn.net>
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To: Randy Bush <randy@psg.com>
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Cc: perpass@ietf.org
Subject: Re: [perpass] Another mail-related proposal
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On 08/19/2013 05:38 PM, Randy Bush wrote:
>>> and the nsa pwns the disk drives of the smtp relays.  e2e, please, in
>>> addition to transport.  in 1984, all data and traffic should be
>>> encrypted.
>> That goes to the question I had in my original message on this thread:
>> what is the threat model we are attempting to address? In the short term
>> at least, I consider transport-level encryption of email to be helpful,
>> because it raises the required attack complexity.
> i agree transport should be encrypted.  and, as someone has pointed out,
> we should know when that negotiation is not successful and be able to
> make some decisions.
>
> smtp is hop by hop.  just because A encrypts to B, A has zero assurance
> that B encrypts to C.  hence, e2e encryption is pretty much mandatory
> against a purely passive attacker.
>
...which goes back to the original thing I was suggesting: that A should
be able to signal to B that it should only relay the message (e.g., to
C) if the channel is also encrypted and that C also will observe the
restriction if it needs to relay the message further. Not as good as
end-to-end encryption, but an improvement nonetheless.

I believe the military folks might call this "Encrypt For Transmission
Only".

-Jim