The WebID Protocol & Browsers

Position Paper for W3C Workshop on Identity in the Browser 24/25th May 2011, Mountain View (USA)

Presented by members of the W3C WebID Incubator Group



1. Position Statement

The browser is both the interface to the Web as well as presenting the user's face to the world. The browser user should therefore be conscious of the face he is presenting at any time. He should be able to change it easily: identity selection should be a one-click gesture, cryptographically-secure, and web site independent. It should put the user in control of the information he shares with each site. And it should be available now.

The WebID protocol enables all of the above. It works in all browsers that correctly implement HTTPS and client-side certificates. But with a twist: it ties those certificates into the web in a RESTful manner allowing identities to be linked together in a secure social web of trust, that does not require central authorities, and that allows the user to control how he describes himself to each site he logs into.

After describing the WebID protocol and its benefits, we will suggest a roadmap for future improvements in the browser that can take advantage of it.

2. WebID Overview

To illustrate how WebID works, we will first look in detail at what happens on the wire when Bob connects for the first time to a protected resource on Alice's Web Server. This resource could simply be a login button, or it could be any of the resources published there. This should help show just how simple and efficient the protocol is: it requires only one more HTTP connection than the original resource requested, and the results of this connection can be cached.

  1. Bob requests Alice's protected HTTPS resource
  2. Alice's web server requests the client certificate on the TLS connection started above
  3. Bob's browser presents him with a selection of identities to choose from:
    Having selected one, the corresponding X509 certificate is sent to Alice's server:
      Public Key Info:
          Public Key Algorithm: rsaEncryption
            Public-Key: (1024 bit)
              00:e8:f9: [snip] :c6:af:2e
            Exponent: 65537 (0x10001)
          X509v3 extensions:
            X509v3 Subject Alternative Name:
    It contains Bob's WebID, shown in bold red above.
  4. Alice's server:
    1. checks that Bob's browser is in possession of the private key corresponding to the public key sent in the certificate, as specified by TLS
    2. extracts the URI from the Subject Alternative Name field of the certificate, which is known as Bob's WebID: a global identifier that refers to Bob via a document that describes him, in a machine readable way using W3C standards.
  5. Alice's server fetches Bob's WebID Profile at in the example if an up to date version is not in the cache
  6. Alice's server checks that the profile relates Bob's WebID to the public key found in the certificate. If they match then she knows that she is in communication with the agent referred to by
  7. Bob's identity is then checked as to its position in a graph of relations in order to determine trust according to some criteria decided by Alice combined with information from the cloud.
    This is outside the core of WebID, but it is important to understand how it can work. Alice might decide for example that only a group of friends who have given her a WebID personally may have access. Or she may be more lenient, and allow any of the friends of those friends to also access that resource, as specified by them in their profile located on their servers. Or she may only trust employees of her company, or of her department, to view that resource. Alice's server can do a lookup in a local file, crawl the web at intervals, or use web services to gather the data to help make that decision.
  8. Access is granted fully, partially, or denied and a representation is returned. Assuming the resource requested is a friend graph, a full representation could be returned to a friend, and a very limited one to an anonymous user.

The WebID placed in the X509 Certificate can be a https URL as shown above. Although the HTTPS scheme is currently the most widely implemented, WebID could also used with any dereferenceable scheme such as ftps://, ldaps://, xris://, accnt: (used by webfinger ). It could also be used in future schemes such as httpk that would give up human readable URIs in order to avoid the centralisation problems of DNS.

3. Advantages of WebID

Issues of identity and privacy have been growing increasingly serious as the Web has become social over the last decade. Remembering login details has grown into a serious security issue as more sites asked for them than people had the ability to remember. And the inability to easily share restricted information across websites has become a visible problem to 100s of millions of people as they started finding themselves and those they wished to communicate with split across siloed services.

Specifically, WebID offers the following advantages.

3.1 Overcoming Password Fatigue

Passwords are difficult to remember or they are easy to crack. As a result people tend to re-use them, making phishing attacks the biggest threat on the web, leading to a mistrust of new services. WebID uses TLS-client certificates and public key cryptography as shipped in current browsers in a way that enables the same certificate to be used across sites securely. Furthermore with the HTML5 supported keygen element, creating such a certificate is as easy as submitting an HTML form.

3.2 OpenID

OpenID reduces the account multiplication issue by allowing users to login to every site using the same global identifier. This provides a base from which WebId can be deployed, procuring the following extra advantages:

These protocol simplifications create a cascade of additional benefits. WebID can be applied recursively, enabling the Relying Party (Alice above) to identify herself using WebID, making it easy to build an authorisation protocol. WebId takes full advantage of the peer to peer nature of the Web.

3.3 Public Key Infrastructure

TLS-client certificates have been available in the browser since 1996, but their usage has been limited to a small number of sites. The organisation which generates the certificate is usually the same as the one that consumes it, giving the user little advantage over username/passwords layered on server-side https. Outside of very large and well-funded Defence related organisations, client-side certificates have thus had very poor adoption.

The missing link to wide adoption is the global naming system that OpenID takes advantage of with URLs, and that allows one to potentially authenticate to all sites. What failed TLS was that X500 names were not Universal Identifiers, were not designed to form an interlinked web, and hence were not usable to authenticate to sites without those first having a federated agreement. One can easily imagine how much resistance there would have been to global hypertext system if organisations had to first make an agreement with every web site they wanted to visit, before their users were able to visit them.

Having solved the naming/identity problem using standard URLs, WebId authorization agents can then use the web of interlinked profiles and other resources (eg. academic publications, ...) to calculate trust in a dynamic manner. Since trust can then be spread to a much larger network of actors, each confirming different pieces of the graph, this allows both greater resilience in the system and more flexibility.

3.4 Future Proof Protocol

Not only does WebID work with the Web as it is today, but it will be strengthened with the rollout of critical infrastructure elements such as DNSSEC, which can be used as Dan Kaminsky explains in his DNSSEC Diaries to publish public keys of services, a work being developed formally by the IETF Dane working group. This can be used to increase trust in all server certificates, but in particular self-signed server certificates, which according to a report by the EFF Observatory are three times more numerous than CA-signed certificates. By lowering the entry barrier to using cryptography, both WebID and Dane will help bring about an increasingly-secure Web.

4. Recommended Browser Improvements

All current browser-based authentication methods fail to give full control over identity to the user. We declare that browsers MUST give the user full visible control of their identity. With TLS, as with cookies, one should be able to see clearly which identity one is logged in under and be able to easily become anonymous again, as far as that is possible of course. The Firefox Weave team have shown what this could look like, making use of the URL bar's existing role as guarantor of server identity and extending it to client identity.

Here the user can see what persona they are presenting to the site or if they are anonymous. It also permits the user to change identity or to log out. The browser could then make use of the information found in the WebID profile--linked to from the X509 certificate--such as finding a link to a picture which could then be displayed, or linking to the account management page as shown above.

This WebID anchor can then be used by browsers to improve the user experience by:

5. Conclusion

WebID allows users to authenticate easily and securely to any website in the world in a one click gesture without needing to fill out any new forms. That site can immediately personalise the experience given the information and social graph made available to it by the user (see Sketch of a RESTful photo Printing service ). This will allow innumerable applications to be built that improve relations between individuals and their friends, co-workers, employers, and vendors across domain and organisational boundaries.

The W3C WebID Incubator Group is keen to work with browser vendors and Web service providers to help standardise the necessary formats, semantics, and RESTful protocols and to provide test suites for these. We are also keen to work with the Federated Social Web XG to build interoperable services in order to discover what gets adopted, standardise those pieces that are most widely agreed on, and discover issues that require longer term research to be resolved.

6. Additional Resources