Re: [pkix] Self-issued certificates

王文正 <wcwang@cht.com.tw> Tue, 21 July 2015 13:47 UTC

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From: =?utf-8?B?546L5paH5q2j?= <wcwang@cht.com.tw>
To: PKIX <pkix@ietf.org>
Thread-Topic: [pkix] Self-issued certificates
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Date: Tue, 21 Jul 2015 13:47:18 +0000
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Subject: Re: [pkix] Self-issued certificates
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> While rolling over a self-signed certificate while preserving trust is an interesting problem (to me, anyway, 'cause I'm a fan of key continuity management ;) in general practice your example chain should never occur in TLS/SSL.  Rollover messages are certificate management messages; new-with-old and old-with-new are management artifacts and not intended for path construction.
> 
> I.e., if in your example:
> 
> - Root rollover is due to pending or past root key expiration, then the "old-root" trust anchor is replaced by "new-root;" the chain terminates at "new-root" and new-with-old doesn't appear.

You are right, if the new root cert (new-with-new self-signed cert) has been distributed to relying parties, then the relying parties can directly use the new root cert as the trust anchor and therefore they do not need to build the certification path with the help of the new-with-old self-issued cert anymore. In the situations where relying parties already has the new root cert in their lists of trust anchors, the certification path will be as follows:

new root cert --> intermediate CA cert --> TLS/SSL cert

However, most relying parties rely on COTS such as browsers or operating systems to update their lists of trust anchors. After a root CA performed its key rollover, it will submit its new root cert to "Root Certificate Programs" of all mainstream browsers or operating systems. It might take server months or even more than half year before the new root cert is accepted by "Root Certificate Programs" of all mainstream browsers or operating systems. Before the new root cert is added to the lists of trust anchors of all mainstream browsers and operating systems, TLS/SSL servers would temporarily rely on the new-with-old certificate to assist relying parties to chain the certification path up to the old root cert (i.e., the old trust anchor).

> 
> - Root rollover is due to root key compromise, new-with-old can't be trusted, "old-root" trust anchor must be removed, and the chain is invalid.

Yes, if the old root key was compromised, then both new-with-old and old-with-new are useless. In that situation, the root CA has to generate a new key pair and distribute the new root cert to relying parties as soon as possible. However, if a root CA of which root key had ever been compromised, I doubt that relying parties will trust the CA again.

Wen-Cheng Wang

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