W3C home > Mailing lists > Public > public-credentials@w3.org > November 2019

Re: Proposed work item: WebKMS

From: Manu Sporny <msporny@digitalbazaar.com>
Date: Sun, 24 Nov 2019 10:27:38 -0500
To: public-credentials@w3.org
Message-ID: <44966202-ef46-ac14-62e4-d598bfbdc937@digitalbazaar.com>
On 11/24/19 1:23 AM, Anders Rundgren wrote:
> Hi Manu, From the ZCAP-LD draft:
> "Web-based applications could provide choice in Key Management 
> Systems -- potentially allowing customers to bring their own Key 
> Management Systems with them just as they bring their own devices 
> today"
> Wouldn't it be logical to have KMSes in these devices as well?

Yes, either in the devices (where the WebKMS driver is WebAuthn) or
using the device's keys to access a remote HSM (where the WebKMS driver
is something like AWS Cloud HSM).

All the pieces are there today... mobile phones do have HSMs that are
accessible via native applications and soon to be broadly accessible via

> I may [surely] be biased but this is at least what my 10Y+(!) 
> SKS/KeyGen2 project builds on. The (ab)use of W3C's PaymentRequest 
> made it pretty cool as well :-) 
> https://cyberphone.github.io/doc/web/calling-apps-from-the-web.pdf

Yes, and this is why the Credential Handler API (CHAPI) is designed the
way it is and supports not only sending Verifiable Credentials through
CHAPI, but ZCAPs as well. CHAPI was built from years of hard won
knowledge gained (and mistakes made) during the creation of Payment
Request and Payment Handler in the Web Payments WG.

> The use-case you mention like car keys are very interesting but I 
> can't imagine that car keys would be stored anywhere but in client 
> devices. Now, how do you get such keys? In my world through 
> (non-standard) authentication to a service provider.  I.e. I (FWIW) 
> do not see that an end-user would ever talk directly to a cloud-HSM, 
> that's reserved for service providers.

Yes, keys can be on client devices, and they can also exist in the
cloud, and it's up to the application to determine which keys will be
used to do what.

WebKMS provides the added flexibility of being able to lose your phone
and all of your phone HSM keys, but not have to rotate out your signing
keys, which exist in the cloud HSM. WebKMS isn't really meant to be
accessed directly from the Web, but will most likely sit behind an
agent/digital wallet of some kind.

To summarize, these scenarios are possible via WebKMS:

* Local HSM only
* Cloud HSM only
* Local HSM that authzs to Cloud HSM
* Local HSM that authzs to shared Cloud HSM (multisig)

... and the benefit of WebKMS is that the same operations are possible
via a unified API for the four scenarios above. Clearly, lots of
discussion needs to happen, and this isn't as fundamental as VCs and
DIDs... but if folks want to do key management in an interoperable way,
WebKMS is one possible way forward.

-- manu

Manu Sporny (skype: msporny, twitter: manusporny)
Founder/CEO - Digital Bazaar, Inc.
blog: Veres One Decentralized Identifier Blockchain Launches
Received on Sunday, 24 November 2019 15:27:44 UTC

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