[TLS] Re: [External⚠️] Re: Certificate Update in TLS

[Watson Ladd <[e-mail]>]

On Fri, Jun 20, 2025 at 3:20 PM Yaroslav Rosomakho
<[e-mail]> wrote:
>
> Hello Watson,
>
> On Fri, Jun 20, 2025 at 10:50 PM Watson Ladd <[e-mail]> wrote:
>>
>>
>> What exactly is the rationale here? Do we expect that identies
>> actually change when a certificate expires?
>
>
> Certificate confirms identity information for a certain period of validity as long as it is not revoked. Communication with an endpoint that produces a revoked or expired certificate is deemed to have unacceptable risk and typically denied. However, this risk applies to established sessions in exactly the same way as it applies to new sessions. The rationale is to ensure that the peer identity is still valid by the time the original certificate expired or got revoked.

Certificate expiry is in some sense driven by the risk of key
compromise. If the key is compromised it fails to provide assurance as
to the identity of the counterparty. But that compromise could also
happen to the keys protecting the session over that length of time
(yes, there are some differences in threat model depending on how they
are stored). In that case this draft doesn't actually protect
anything: an attacker with those keys is able to see the traffic going
through and continue to exploit the session.

This isn't really a problem of identities expering (how could they)
but rather risk limitation.

The reason I belabor this point is the conclusion: we have to rekey
the connection as well to get the assurances we want. The mechanism
here doesn't do that.

>
> TLS 1.2 and prior could perform re-key and re-authentication through rehandshake. As the very generic rehandshake carried unacceptable security risks it was removed in TLS 1.3. Extended Key Update brings back re-key in a secure way. Similarly, Certificate Update proposal is intended to bring back re-authentication in a very limited controlled fashion.
>
> Best Regards,
> Yaroslav
>
>
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