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

Re: the intersection between Swagger-style APIs and SSI/decentralized identity

From: David Chadwick <D.W.Chadwick@kent.ac.uk>
Date: Mon, 30 Dec 2019 20:40:10 +0000
To: public-credentials@w3.org
Message-ID: <82516382-a5fe-7524-7fbc-ce5e567ca5fc@kent.ac.uk>
I would like to add to this discussion that the ISO mobile driving 
license working group has been working on various alternative protocols 
between the holder and verifier for several years, and have fully worked 
out protocols for the holder to present his mDL to the verifier via 
bluetooth and 2D bar codes, assuming that the user is not connected to 
the Internet, as well as online protocols, one being based on OIDC. 
Given that we are actively working with this ISO group to persuade it to 
adopt the VC data model, we could reciprocate by adopting some of their 
transfer protocols, and contributing to their efforts in order to have a 
joint ISO/W3C set of protocols for transferring VCs from the issuer to 
the holder to the verifier. Given that one of the most popular VCs is 
likely to be a driving license, then we can all benefit from 
collaborating with the ISO group and using the same protocols, rather 
than fragmentation and expecting users to support multiple protocols 
with different ones being used for driving licenses and other VCs. May 
2020 be the year of collaboration.

Happy New Year


On 30/12/2019 19:54, Daniel Hardman wrote:
> Markus has recently proposed a work item for the CCG to develop 
> Swagger-style APIs for issuers and verifiers. Justin has recently 
> proposed a charter for a TxAuth group to start working on HTTP-based 
> APIs to accomplish delegation. Digital Bazaar has advocated their 
> RESTful Credential Handler API (CHAPI) in CCG and other circles as 
> well. No doubt many others on this thread are aware of efforts to 
> standardize APIs with similar style and similar intersection to the 
> SSI/decentralized identity space.
> I would like to raise a red flag about such efforts, and trigger a 
> thoughtful follow-up conversation. I love Swagger-style APIs and have 
> advocated them extensively at past junctures of my career, but I am 
> concerned that they are exactly the wrong thing to standardize right 
> now. I'll explain my concerns below, in red, and then offer an 
> alternative path that has most of the same benefits, in blue.
> 1. RESTful APIs are web-only.
> How do two farmers with cheap android devices in the highlands of 
> Bolivia (or a Canadian Mounty and a speeder on a lonely highway in 
> Yukon Territory, or friends in Frankfurt whose cell service has a 
> brownlout, or two anti-government protesters) use RESTful APIs to 
> transact business? If the answer is, "they subscribe to a service in 
> the cloud so they can talk device-to-device," I hope we are 
> embarrassed. We need something that also works over BlueTooth and 
> email and other transports where a web server isn't a component.
> By standardizing a solution that doesn't think about these scenarios, 
> we are further marginalizing them, and we are enthroning a 
> /you-must-be-connected-and-you-can-be-surveilled/ model that 
> guarantees /it-isnt-a-standard/ FUD for any other efforts to fix the 
> problem.
> 2. RESTful APIs perpetuate the PKI model that we claim to be replacing 
> with DIDs.
> Servers are authenticated in these APIs with a cert. Clients are 
> authenticated with a session that follows from an OAuth token or an 
> API key or basic auth material. It is possible to imagine "DID Auth" 
> being used for a client of a RESTful API, and there have been several 
> efforts to describe and standardize such a thing. So far, none has 
> meaningful traction, so all APIs in the SSI space that use APIs are 
> also allowing non-DID authentication for clients. But even if we solve 
> the problem for the client side, nobody is proposing to solve the 
> problem for the server side. Institutions in these APIs don't use DIDs 
> for anything meaningful. Thus none of the decentralized properties of 
> DIDs are brought to bear for the server side of the interaction, and 
> any decentralized qualities of DIDs are relegated to minor, optional 
> status for clients.
> 3. RESTful APIs foster a power imbalance
> What if there's a standard way for institutions to be a verifier or 
> issuer, but no way for ordinary people to be a verifier or issuer? Or 
> a standard way for institutions to delegate, but no way for ordinary 
> people to do it? That's effectively what APIs like the ones I 
> mentioned above guarantee. There are multiple reasons why, including:
>   * Institutions have web servers; farmers in Bolivia don't. (Saying
>     that they *could* is not helpful; we're just creating more
>     adoption burden for SSI by making the tech harder and more
>     expensive for them.)
>   * Servers can't make the first move in RESTful APIs; everything
>     begins when a client initiates the interaction. This makes it
>     natural for an institution (or a regulatory regime) to impose
>     terms of service or reputation criteria on a client, and unnatural
>     for a client to do the opposite. It's also convenient for hackers
>     and surveillers, since they know they can catch all interactions
>     at inception by simply listening on the server.
>   * Because these APIs are online-only, and because the server always
>     waits for the client to make the first move, they can only be
>     operated by those who have a 24x7x365 cloud presence. Institutions
>     and ordinary people don't have equal access to 24x7x365 cloud
>     capabilities.
>   * Because these APIs are secured on the server side by a cert, they
>     can only be operated by those who have access to expensive,
>     premium, centralized reputation. Again, institutions and people
>     don't have equal access to this.
> This is not an exhaustive list of my concerns, but I think it's enough 
> to trigger a conversation.
> Proposed Alternative
> We create web APIs, but we think about them differently. We conceive 
> of all of them as exchanges of messages that could also be 
> accomplished over BlueTooth, email, etc. HTTP(S) is just another 
> transport, where messages happen to be passed by HTTP POST (or GET, as 
> appropriate). Security properties associated with the exchange are 
> based on the control of DIDs and embodied in the messages themselves 
> (e.g., through encryption/signing), not in a transport layer. All 
> semantics for the interaction are conveyed by the message content. The 
> traditional URL namespacing of Swagger can still exist, but it becomes 
> less interesting, since the message content must be enough to convey 
> semantics on its own (so the messages are enough in other transports). 
> Either party can initiate an interaction. Institutions and people are 
> actually peers.
> This is the world of didcomm and application-level protocols built 
> atop it; it's described in Aries RFC 0003 
> <https://github.com/hyperledger/aries-rfcs/blob/master/concepts/0003-protocols/README.md>. 
> But before folks get their hackles up about not wanting to work with 
> Aries or DIF, note that I didn't propose that Aries protocols have to 
> be the basis for this approach. Instead, I proposed some 
> characteristics we need to avoid. Can we explore that assertion on its 
> merits, without getting immediately entangled in politics?
> There are already maybe 8-10 software stacks, some independent from 
> top to bottom, that implement an "API" for issuing credentials and an 
> "API" for verifying presentations based on the model I just 
> articulated. These implementations are demonstrably interoperable with 
> one another. By proposing a new work item for a Swagger API for 
> issuance and verification, we are walking away from interoperability 
> with these implementations, and we are incurring all of the 
> architectural disadvantages I highlighted in red above.
> What if we did this instead?
>   * Agree that for issuance and verification, the goal about payloads
>     and sequencing for HTTP calls should be alignment between those
>     defined in the Aries protocol and those used by people who aren't
>     Aries-centric. This could involve give and take in either
>     direction; I'm not proposing that it has to be done by simply
>     adopting the Aries work.
>   * Agree not to depend on HTTP-specific constructs (e.g., HTTP
>     headers, HTTP status codes) to signal important semantics--so the
>     payloads could be exchanged over BlueTooth or email just as easily.
>   * Agree that, while URL namespacing gives us a nice hook into
>     Swagger-oriented tools, all semantics required for the interaction
>     are detectable from the payloads themselves.
> Then we'd have an HTTP solution that is Swagger-compatible but not 
> limited to HTTP. The "API" we created would be interoperable on a much 
> broader canvas than simple web.
> If we further agreed to this:
>   * Authentication of both parties in the interaction will be done on
>     the basis of DID control, not on the basis of certs.
> Then we'd also eliminate the dependence on the web's flawed PKI model, 
> and the power imbalance of today's web. But I know this is more 
> controversial.
Received on Monday, 30 December 2019 20:40:19 UTC

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