Re: [OAUTH-WG] DPoP key rotation

[George Fletcher <[e-mail]>]

There has also been some limited discussion on whether it's useful for 
mobile applications to create a relationship between keys used for 
Dynamic Client Registration (DCR) and the associated keys for DPoP 
headers. DCR does have mechanisms for rotating client instance keys and 
hence if the keys for DPoP are the same then this might be a mechanisms 
to support rotation for mobile applications.

Note that while both Android and iOS have hardware support for keys... 
the keys themselves have limitations on how they can be used, so 
depending on your use case, the hardware backed keys may not suffice.

Thanks,
George

On 6/11/21 4:20 PM, Brian Campbell wrote:
> Hi Dmitry,
>
> This ML is indeed the appropriate place for this kind of thing. You 
> raise a legitimate question, however, the general rough consensus 
> thinking has been that allowing for DPoP key rotation for refresh 
> tokens and public clients (the only case where it's relevant) didn't 
> add enough value to justify the added complexity. It doesn't help with 
> the threat model for in-browser applications. And mobile applications 
> have really good options for key storage - to the point that the kind 
> of event that might compromise a DPoP key would involve a lot more 
> than key rotation to cleanup from.
>
>
>
> On Tue, Jun 8, 2021 at 10:31 AM Dmitry Telegin 
> <dmitryt=[e-mail] 
> <mailto:[e-mail]>> wrote:
>
>     Hi,
>
>     I'm Dmitry Telegin, I'm currently working on DPoP implementation
>     in Keycloak on behalf of my company, Backbase. Takashi Norimatsu
>     of Hitachi supervises this process as the head of the Keycloak
>     FAPI SIG.
>
>     With the current DPoP design, once the keypair has been generated
>     on the user agent and the initial token set has been obtained
>     (using authorization_code grant), the whole chain of the
>     subsequent access/refresh tokens will be bound to this particular
>     keypair. That means, the keypair should be persisted on the user
>     agent for the duration of the session.
>
>     OTOH, sessions could be rather long-lived, especially if we take
>     offline tokens [1] into account. In a nutshell, offline access
>     provides a non-expiring refresh token. This could be highly
>     relevant e.g. for mobile applications that would employ offline
>     tokens to help users avoid logging in every time.
>
>     The longer the session lasts, the higher the probability of key
>     leakage is. Currently, the only way to switch to a new DPoP
>     keypair is to start a new session (i.e. log in again). Do you
>     think it might be worth incorporating some sort of key rotation
>     concept into DPoP design?
>
>     The most obvious way to perform key rotation is to do that during
>     token refresh. For that, we could make the refresh_token grant
>     honour the additional DPoP proof that would supersede the current
>     one. From the technical PoV, it could be as easy as supplying two
>     proofs within the DPoP header:
>
>     |DPoP: eyJ0eXAiO... eyJ0eXAiO... |
>
>     |Or we can go with a single (old) DPoP proof, containing the new
>     proof (to supersede the current one) as a claim (or vice versa). |
>
>     |We'd appreciate any feedback from the WG. Also apologize if this
>     ML is not the appropriate place to discuss issues like this. |
>
>     |Regards, |
>
>     |Dmitry Telegin |
>
>     |Senior Backend Engineer, Backbase R&D B.V. |
>
>     [1]
>     https://openid.net/specs/openid-connect-core-1_0.html#OfflineAccess
>     <https://openid.net/specs/openid-connect-core-1_0.html#OfflineAccess>
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