[Ovmsdev] Urgent TLS root certificate issue (Let's Encrypt)

Mark Webb-Johnson mark at webb-johnson.net
Thu Sep 30 13:02:49 HKT 2021


Let’s Encrypt say that because there are a lot of embedded devices that do not update firmware / trusted CA lists, they did it this way. They are also worried about older Android devices that can’t be updated.

IMHO, they made a bigger mess of it by using cross-signing and introducing SSL/TLS library compatibility issues. The X3 trusted CA cert that was expiring could have simply been renewed without requiring a new one, and maintaining compatibility and a smooth transition. These CA certs are self-signed anyway, so you can do whatever you want with them (and I’ve done the 10 year re-sign twice already for my day-job primary CA).

Regards, Mark.

> On 30 Sep 2021, at 12:42 PM, HONDA S2000 <s2000 at audiobanshee.com> wrote:
> Sorry to jump in the middle (end?) of a long thread...
> Working on another system at work a couple of years ago with embedded security, I recall a couple of topics from the design meetings.
> 1) Certificate handling should be designed to allow for a transition period where two equivalent certificates are valid at the same time. That's because it's almost impossible to roll out a certificate change in the deployed fleet if only one can be valid at a time. The duration of the overlap needs to be long enough for all systems to transition, and only then can the old certs be removed.
> 2) Intermediate certificates are what enables these changes. The top or root cert is usually too protected to allow easy changes, or managed by another entity, so the team / project gets an intermediate that can be used to sign multiple leaf certs with varying expirations.
> Leaf certs change relatively quickly, while intermediates change relatively infrequently. In both cases, some overlap time needs to be supported. I suppose this means that the root cert also needs a plan for transition that doesn't abruptly cut off all working systems.
> Unfortunately, you probably already know all of this, and I'm just not familiar with how OVMS handles certs. But basically, I'm wondering whether a smoother transition can be designed around the *next* expiration. ... or is this something that Let's Encrypt didn't plan for?
> Brian Willoughby
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