Secure email (was: Re: [friam] and so it goes )

On 1/18/2016 8:57 AM, Sandro Magi wrote:
> Certainly a marked improvement over unencrypted content, but it doesn't handle
> key expiry. Once my key expires, all my subsequent e-mails to you will not match
> the public key you stored, so what's a key update protocol that's also secure?

Thanks for the comments.   When your key expires (e.g. you reinstall 
your software or even a timeout), if you send "me" an email my client 
will recognize the new public key from a recognized "from" address, 
notify me (if I care), and save the new key.
If I care about the notification I can do whatever I wish to reestablish 
trust with the sender with the new key.  In the rare but important (e.g. 
legal or financial) case where a key is bound to a person or institution 
then a new key binding must be done (see below for details).

If your key expires and 'I' send you a message before you send me one 
then your client will respond with a "key change" message (rather than 
displaying the distracting cypher text) - resulting in the situation above.

Since I mentioned "key binding" above I may as well restate a simple 
protocol that I believe can leverage a secure web site login (common for 
financial/legal sites) to establish a key binding for secure email.  I 
login to my web site and submit my email address and its associated 
public key to a form.  The web site binds that public key to the email 
address.  Thereafter any email signed by my private key can be assumed 
to be from me - until my key expires, when I need to do a rebinding.  
Anybody see any problem with that protocol?

For typical email use, however, I don't consider key binding a 
significant issue.  I'd be quite comfortable just accepting a new key 
binding from anybody sending email to me in nearly all circumstances.  
Even if I do so without any check or exchange I'm better off than I am 
now as at least ALL messages will be encrypted and signed - even if the 
sender isn't necessarily bound to a specific person or institution.  
Having been notified of and accepted a new key binding to an email 
address, I might be on somewhat more alert about a potential man in the 
middle attack, but how often do I care?  I certainly don't have any 
support for caring now.  If I did care in future I could do key binding 
more generally (e.g. testing via alternative communication such as 
telephone, video chat, or whatever).  As I say, I really don't see key 
binding as a practical problem except for very rare cases where 
something like the key binding through a secure web login (as above) 
seems perfectly adequate to me.

> Encrypted messages also reduces the effectiveness of search, which is a big
> issue with today's e-mail volume.

Are you referring to searching my own email archive?  In that case why 
can't it just be the clear text that is saved and searched?

If you are referring to some other email being searched, please clarify 
why one would need to "search" encrypted email.

--Jed