Re: [lamps] Call for adoption of draft-becker-guthrie-cert-binding-for-multi-auth-02

["Kampanakis, Panos" <[e-mail]>]

You are proposing that two different identities can be deduced to be the same because at issuance one of the identities proved to own both keys. That is a redefinition of PKI and potentially dangerous. As a verifier, I am only talking to one identity at a time. So if my peer gives me two certs, they better be issued to the same identity I am talking to or I will fail authentication. As a CA issuing two certs to two different identities, I would be uncomfortable if I knew that cert X was validated by a verifier just because cert Y was related to it and the identity in Cert Y was correct.


From: Spasm <[e-mail]> On Behalf Of Mike Ounsworth
Sent: Thursday, January 26, 2023 6:17 PM
To: Michael Markowitz <markowitz=[e-mail]>; Santosh Chokhani <[e-mail]>; [e-mail]
Subject: RE: [EXTERNAL][lamps] Call for adoption of draft-becker-guthrie-cert-binding-for-multi-auth-02


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At the risk of getting baited into a religious war, when it comes to statements of “these two things are related”, the definition of “weak” is relative.


Name matching proves that the two keys are owned by the same entity, for some potentially weak definition of “same entity”, depending on how the PKI is operated. For example I have a driver’s license and a health card, but they are not really “connected”.

Simultaneous proof-of-possession or usage of two private keys proves that they exist together, accessible by the end entity at the same time. If I present my health driver’s license and health card together at the same time, then they start to be connected.

If the issuer validates PoP of both keys at issuance time and cross-links the two keys (via some sort of X.509 extension), then you have you have a statement from the authority which is “stronger” than name alone that these two specific certs are a pair. Like if my driver’s license and health card were issued on the same day with the same photo and have matching serial numbers.

Bonus points if you have key attestations for both keys proving that they live in the same piece of hardware. The same piece of plastic serves as driver’s license and health card.

When it comes to statements of “these two things are related”, the definition of “weak” is relative.

---
Mike Ounsworth

From: Spasm <[e-mail]<mailto:[e-mail]>> On Behalf Of Michael Markowitz
Sent: Thursday, January 26, 2023 4:36 PM
To: Santosh Chokhani <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: [EXTERNAL] Re: [lamps] Call for adoption of draft-becker-guthrie-cert-binding-for-multi-auth-02

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Santosh wrote:

>If the authors have not already done so, I would propose that there are ways the extension can provide crypto binding between/among the certificates which would be superior to simply name >matching.  Name matching is weak.

If you’re claiming *notarized* name matching is weak, I think we have to throw out the whole concept of X.509 certificates!  😊

-mjm
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