On Aug 28, 2013, at 11:03 AM, Jonathan Thornburg wrote:

> On Wed, 28 Aug 2013, Jerry Leichter wrote:
>> On the underlying matter of changing my public key:  *Why* would I have
>> to change it?  It's not, as today, because I've changed my ISP or employer
>> or some other random bit of routing information - presumably it's because
>> my public key has been compromised.
> Maybe it's because you've forgotten the passphrase guarding the
> corresponding private key?
> Or because you'd like to do the electronic equivalent of "change my name,
> start [this facet of] my electronic life over"?
The point of my question was that for different reasons for changing the public 
key, there are different issues and different potential responses.

- If I need to change because the private key was compromised, there's nothing 
I can do about past messages; the question is what I do to minimize the number 
of new messages that will arrive with a now-known-insecure key.  This was the 
case I assumed the previous poster was concerned with.
- If I lost the private key, all previous messages remain secure - except they 
are now, unfortunately, secure against me as well :-(.  New messages sent with 
the key will be unreadable, but if I am in a position to determine who sent 
them, I can tell them to re-send with a different key.  If the system is set up 
so that even return information is encrypted, I'll have to rely on my 
correspondent's realizing they need to re-send via some other mechanism.  (It 
could be through whatever revocation mechanism the system has; it could be 
through mail I send to everyone I correspond with; it could be through a phone 
call, or just by word of mouth.  The sender will have to check the dates and 
realize that some message was sent recently enough that I probably couldn't 
decrypt it.)
- As I outlined things, there was never a reason you couldn't have multiple 
public keys, and in fact it would be a good idea to make traffic analysis 
harder.  Adding a new key for "a new facet of your electronic life" is trivial.

                                                        -- Jerry

> -- 
> -- "Jonathan Thornburg <jth...@astro.indiana.edu>
>   Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
>   "There was of course no way of knowing whether you were being watched
>    at any given moment.  How often, or on what system, the Thought Police
>    plugged in on any individual wire was guesswork.  It was even conceivable
>    that they watched everybody all the time."  -- George Orwell, "1984"
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