Re: hardware tokens and subkey rotation [was: Re: Get your free Yubikey sponsored by Infomaniak (available for free for any DD and DM)]
On 04/17/2018 12:33 AM, Daniel Kahn Gillmor wrote:
> On Mon 2018-04-16 22:23:57 +0200, Thomas Goirand wrote:
>> Easy: we just make the new subkeys on a new Yubikey, and keep 2 keys for
>> a short time (a month or 2, which is enough for the Debian keymaster to
>> update the keys). That's ok because we have lots of spare Yubikeys. I
>> guess it should be a way more annoying if you don't.
>
> hm, so are you encouraging people who get these hardware tokens to get
> two of them
This is what we do here because we have lots of Yubikeys available, I'm
not saying this fits everyone. Having expiration dates on subkeys is a
good idea for everyone, but maybe generating new subkeys when they
expire isn't (ie: just changing the expiration date 1 month before they
expire is enough).
>> After that period, we can still use the old saved .gnupg that we store
>> on an encrypted USB key, together with the private part of the master
>> key. We got to make sure we have access to the private part of the
>> master key to exchange key signature anyways, even if the point of
>> having subkeys is to *not* store it on our laptops.
>
> i see, so reading old encrypted messages involves exposing the master
> secret key as well?
Yes, though it should be an exception, the general use case is that it
should not happen: if you publish the new subkeys early enough, new
messages will be using the new subkey.
> The most important security added by rotating your
> decryption-capable subkey comes in when you can actually *delete* the
> private part of the subkey. When you can do that, then anyone who has
> captured encrypted messages to that subkey can no longer force the
> secret key out of you to decrypt the message.
Oh indeed!
Then probably we should just accept the fact that, when someone encrypts
a message with the old key, we can't read it, and we have to ask for a
new message to be sent. I don't think that's a big problem.
Cheers,
Thomas Goirand (zigo)
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