[pkix] Upgradable/Replaceable IoT systems. Re: Managing Long-Lived CA certs

Anders Rundgren <anders.rundgren.net@gmail.com> Fri, 21 July 2017 03:23 UTC

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From: Anders Rundgren <anders.rundgren.net@gmail.com>
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Date: Fri, 21 Jul 2017 05:23:37 +0200
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Subject: [pkix] Upgradable/Replaceable IoT systems. Re: Managing Long-Lived CA certs
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It is not uncommon that there are more than one imaginable solution to a problem.

In this case there is an obvious alternative to what is proposed.
Assume that a system * in some way becomes obsolete.

If such a system represents a considerable investment AND needs to live for decades, it should be upgradable.

If OTOH the system is not upgradable, it should be replaced.

If an IoT device only supports outdated algorithms it is anyway vulnerable to attacks making workarounds on the CA side fairly useless.

BTW, who in their right mind would run a CA with compromised keys or a CA for obsolete devices?

* System in this context involves the entire infrastructure, including possible CAs.

> Hi PKIX,
> I have a small question for the list regarding long-lived CA 
> certificates. Especially in the context of device certificates, we often 
> see the use of extra long-lived certificates for Root and Sub CAs (e.g., 
> 35+ years) combined with limited key sizes (e.g., p256).
> Until we have a supported mechanism for reprovisioning devices (...), 
> one possible solution for limiting the exposure of the private key would 
> be to have a scoped certificate issuance period.
> What I am thinking about would be adding an extension that says: "This 
> CA can issue certificates from up to 5 years from the validFrom, after 
> this, just use it to provide revocation information". This might provide 
> some protection in case the CA key is compromised after the initial 5 
> years of validity (e.g., certificates issued after that date shall be 
> rejected).
> Does such extension exists today ? If not, could this be some work for