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Re: [websec] HPKP & different encodings of the same public key

Yoav Nir <ynir.ietf@gmail.com> Sun, 15 May 2016 20:32 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
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Date: Sun, 15 May 2016 23:32:11 +0300
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To: Yaron Sheffer <yaronf.ietf@gmail.com>
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Subject: Re: [websec] HPKP & different encodings of the same public key
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> On 15 May 2016, at 10:54 PM, Yaron Sheffer <yaronf.ietf@gmail.com> wrote:
> 
>>> On 15/05/16 10:22, Yoav Nir wrote:
>>>> That’s interesting. With HPKP you can pin keys from existing certificates, or keys that are not (yet) in certificates.
>>>> 
>>>> One of the early deployment scenarios (which got de-emphasized later on) was that you include two pins: your current production key and a spare key that you will certify if something bad happens to the production key (like the private key leaking out).
>>>> 
>>>> 
>>> Hi Yoav,
>>> 
>>> I had assumed this *is* the main deployment scenario. If it was de-emphasized, what do you consider as the "classic" HPKP usage scenario?
>> 
>> Current certificate plus some CA certificate that you are likely to use to certify your next certificate.
>> 
>> Yoav
>> 
> 
> But this too means that you're guessing how the CA will behave in the future. If your current cert is expiring in a month and you generate the new one, you can be surprised by the CA using a new intermediate cert.
> 
> And of course, some people would never pin to a CA cert. To me, the whole idea of certificate pinning is to reduce the need to trust the PKI industry, and that includes my own friendly CA.

I agree. Appendix B of RFC 7469 recommends to have the backup pin signed by a different CA and ready to use. That solves the issue of not knowing how a CA might encode the SPKI. It used to be a costly solution, but these days a certificate is pretty much free, so you really can have a backup certificate ready to use.

Yoav

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