sign encrypted emails

[Daniel Kahn Gillmor]

On 01/03/2014 12:35 AM, Hauke Laging wrote:
> From the RfC perspective (PGP/MIME) this should not be a problem; you just 
> need another level of nesting. Maybe the mail clients are not even prepared 
> for reading such messages. That would not surprise me but would not be an 
> argument against one client implementing this as the first one. I am 
> interested in general arguments for and against this.

it sounds to me like you might be interested in what the S/MIME
community calls "triple-wrapping", which is used to provide
cryptographic proof-of-origin and attribute-handling for intermediate
transport agents:

 http://www.isode.com/whitepapers/smime-military-messaging.html
 https://bugzilla.mozilla.org/show_bug.cgi?id=380624

That said, triple-wrapping (or similar approaches) have tradeoffs that
we might not want to encourage.

For example, they leak metadata about who signed the message to anyone
who observes it in transit; this is not the case for the traditional
sign-then-encrypt layering.  metadata gathering is a fruitful
surveillance technique.

but at its core, i think the problem you're raising is related to a
fundamental (but probably common) misunderstanding: people assume that
if something is encrypted to them then that is related to some signal
from the message author, even though asymmetric encryption has nothing
to do with authenticity or verifiability.

I don't think you're going to solve that particular problem by having
some e-mails have an extra layer of signature on them.

	--dkg

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