On 7/18/2014 at 1:52 PM, "Robert J. Hansen" <r...@sixdemonbag.org> wrote:
>
>> Symmetric keys and fingerprints have to be exchanged through a 
>secure 
 
=====

I think what Hauke meant was an exchange of the *passphrase* for the symmetric 
encryption, not the session key.

The symmetric keys would always change with each new email message, using gnupg 
symmetric encryption.


The only annoyance with this type of approach, is that it needs a separate 
passphrase for each correspondent,
(which we don't bother with ordinarily, since encrypting the symmetric session 
key to a correspondent's public key makes it unnecessary).


Hushmail has a one-way variant of this approach. 

A Hushmail user can send an encrypted message to someone who does not have 
encryption or Hushmail, by having the Hushmail user give the recipient an 
answer to a question.

The email message is encrypted symmetrically using that answer as a passphrase.
(Hushmail makes it intentionally easier, (albeit less secure),  by making the 
'answer' case insensitive, and ignoring spaces and punctuation characters).

The receiver gets a message that an encrypted e-mail has been sent, and is 
directed to the Hushmail server where the sender's question is asked, and the 
receiver has 3 chances to provide the correct answer.  A correct answer 
decrypts the symmetrically encrypted e-mail and the plaintext is displayed on 
the Hushmail server. The e-mail is removed from the server after 72 hours.

A few people who have received this type of message from me, thought it was 
interesting and convenient, and signed up for their own hushmail accounts, and 
are now well on their way to learning gnupg,
so it might be an approach to get people who have never used encryption, to try 
it.


(My apologies, Hauke,  in advance if I mis-understood you and this discussion).


vedaal


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