Re: [sidr] TA questions

[George Michaelson <ggm at apnic.net>]

On 05/11/2009, at 4:50 PM, Robert Kisteleki wrote:

> Hi,
>
> I'm proxying two questions from our development team regarding the  
> TA draft:
>
> 1) How do the authors envision key roll overs for the RTA?
>
> Even though the draft allows for re-publication of the self-signed  
> RTA with new resources, it does not seem to address key roll overs  
> for that RTA. It seems one would have to publish a new ETA to  
> support this, which would make invalidating the previous RTA (if  
> that's ever needed) difficult.

Nowhere in the document does it say that the ETA and RTA keys are  
linked. Therefore it's not clear to me *WHY* the ETA has to  
necessarily roll when an RTA re-keys.

If an RTA publisher wanted to roll their RTA key, then it seems  
feasible by having the ETA simply use the key conservatively and  
assume an indefinite lifetime. The important caveat is that the RTA  
should be treated with the same level of respect as any trust anchor.

> 2) Can we have a more clear pointer the RTACMS object for relying  
> parties?
>
> The current proposal has the ETA CA point to a directory. See page 7  
> of the draft for an ascii-art representation of this. This means  
> that relying parties will have to find the actual RTACMS object in  
> this directory themselves. Probably rsync the whole thing and loop  
> over the entries to figure out which is which.

Robert, the ETA certificate has an SIA. The ETA SIA *should* point to  
a directory, which will contain a CMS object, and a CRL. It *can*  
contain the ETA too. What else does this directory contain, that a  
relying party is not interested in seeing?

Relying party software, assuming it trusts this ETA, periodically  
scans this SIA space and picks up all valid CMS signed objects and  
loads the payload RTAs, again assuming that it trusts the ETA. It  
needs to see the CRL too.

CMS is quite recognisable, testable, provable. Thats the whole point.  
The ETA can be signing over more than one RTA (for instance, key  
rollover) so there can be more than one CMS bundle to be seen, signed  
by the ETA.

-George