Client Side OpenID

The following article discusses ideas that I wouldn’t even class as vapourware, as I am not proposing to implement them myself. That said, the ideas should still be implementable if anyone is interested.

One well known security weakness in OpenID is its weakness to phishing attacks. An OpenID authentication request is initiated by the user entering their identifier into the Relying Party, which then hands control to the user’s OpenID Provider through an HTTP redirect or form post. A malicious RP may instead forward the user to a site that looks like the user’s OP and record any information they enter. As the user provided their identifier, the RP knows exactly what site to forge.

Out Of Band Authorisation

One way around this is for the OP to authenticate the user and get authorisation out of band ā€” just because the authentication message begins and ends with HTTP requests does not mean that the actual authentication/authorisation need be done through the web browser.

Possibilities include performing the authorisation via a Jabber message or SMS, or some special purpose protocol. Once authorisation is granted, the OP would need to send the OpenID response. Two ways for the web browser to detect this would be polling via AJAX, or using a server-push technique like Comet.

Using a Browser Extension

While the above method adds security it takes the user outside of their web browser, which could be disconcerting. We should be able to provide an improved user experience by using a web browser extension. So what is the best way for the extension to know when to do its thing?

One answer is whenever the user visits the server URL of their OP. Reading through the specification there are no other times when the user is required to visit that URL. So if the web browser extension can intercept GET and POST requests to a particular URL, it should be able to reliably detect when an authentication request is being initiated.

At this point, the extension can take over up to the point where it redirects the user back to the RP. It will need to communicate with the OP in some way to get the response signed, but we have the option of using some previously established back channel.

Moving the OP Client Side

Using the browser extension from the previous section as a starting point, we’ve moved some of the processing to the client side. We might now ask how much work can be moved to the client, and how much work needs to remain on the server?

From the specification, there are three points at which the RP needs to make a direct connection to the OP (or a related server):

  1. When performing discover, the RP needs to be able to read an HTML or XRDS file off some server.
  2. The associate request, used to generate an association that lets the RP verify authentication responses.
  3. The check_authentication request, used to verify a response in the case where an association was not provided in the request (or the OP said the association was invalid).

In all other cases, communication is mediated through the user’s browser (so are being intercepted by the browser extension). Furthermore, these three cases should only occur after the user initiates an OpenID authentication request. This means that the browser extension should be active and talking to the server.

So one option would be to radically simplify the server side so that it simply proxies the associate and check_authentication requests to the browser extension via a secure channel. This way pretty much the entire OP implementation resides in the browser extension with no state being handled by the server.


So it certainly looks like it is possible to migrate almost everything to the client side. That still leaves open the question of whether you’d actually want to do this, since it effectively makes your identity unavailable when away from a computer with the extension installed (a similar problem to use of self asserted infocards with Microsoft’s CardSpace).

Perhaps the intermediate form that still performs most of the OP processing on the server is more useful, providing a level of phishing resistance that would be difficult to fake (not only does it prevent rogue RPs from capturing credentials, the “proxied OP” attack will fail to activate the extension all together).

This Post Has 15 Comments

  1. Andrew

    I think you mean “rogue” RPs, not “rouge” šŸ™‚

  2. Raithmir

    Interesting article, it’s certainly something that should be looked into IMO.

    The main thing that worries me about OpenID is that once someone finds out your password then there’s potentially a lot of sites a hacker has access to, posing as you. More needs to be done, and your suggestions go some way to alleviating that.

  3. James Henstridge

    Andrew: fixed.

    Raithmir: It is true that revealing your OpenID identity’s login credentials gives someone access to many sites, but it is not particularly worse than the current status quo. Most sites use an email address to identify the user, and provide a way to send a “password reset” mail to that address. So if you reveal your mail server login credentials to someone, then they’ve effectively got control of your account on all the sites you used that email address with.

  4. alex

    How about when you register to OpenID you upload a small picture. Then, the login page shows you this picture- say, your face.

    It’s a very visual way of avoiding phishing.

    Disclaimer: I only have some knowledge about how OpenID works.

  5. Christopher

    What I found interesting was the approach that MyOpenID uses, where I believe you can install an SSL certificate direct into your browser from their site. So any time you were forwarded to (what you thought was) MyOpenID and it prompted you for your password (as opposed to doing the SSL magic), you’d know you’re on rogue site.

  6. Rob J. Caskey


    I’m going to me-to the anon fellow above me. Certs are the way of the future, and they should live on the Gnome keychain and be presented in a Cardspace like selector. RPs can select with set of authentication mechanisms they wish to support: my personal preference is that Infocard be the dominate one because Cardspace on windows solves the same problem fairly well, and there are no show-stopper problems with it. The MS-blessed term for generic implementations of Cardspace is Infocard.

    There is already a Firefox plugin that sorta-worked last time I checked on it about 9 months ago, it lives at, but I would love to see it in Gnome proper. SSL certs wouldn’t be bad either, but gnome-integration is a must.

  7. Owen Taylor

    To me, reducing the threat of phishing boils down to to one or both of two things: change around the interaction so that the user never expects to have to enter a password on the web, or to eliminate entirely the existence of a password that is useful to phish. Current methods of improving OpenID (require logging in beforehand, make your OP’s page more verifiably authentic etc), all fall down, because they assume the existence of an alert user who understands what is going on and has a good sense of when something unusual happens.

    Information Cards have some nice properties… in particular they have a well thought-out user interaction model that does not involve entering passwords into a web page. The biggest problem is probably is that implementing them brings in all sorts of WS-* goo. A client side OP sounds a bit like reinventing information cards. But I think at that point you have to ask what the goals are: to integrate into the OpenID ecosystem? to make things easier to implement by not having WS-*? etc. The worst thing would be to end up with the broken OpenID user interaction, but incompatible with both most OpenID RP’s and with information card RP’s.

  8. steve

    I was going to suggest the exact same as Alex above. Require the user to upload some picture(or text for accessibility) that they’ll recognise and expect when they go to their genuine site.

  9. John Drinkwater

    James, You can achieve this using (this does over-XMPP openid auth like you said), and, an XMPP firefox extension. You receive a message when you go to log-in, and all you have to do is reply, and then the stall while waiting for to load, unblocks and you log in to the RP. Pretty simple.

    Personally Iā€™m not going to touch all the *Card* stuff, seems a little ott and.. controlling, Iā€™m quite happy using regular browser certs, the only thing needing improvement is the usability and awareness for newbs.

  10. Frej Soya

    I’ve been thinking/trying to get openid in mugshot/ (only broken patch so far on local disk). Mugshot would improve if it could auto-detect other web”applications” at sign-up time – so it seems like a good place for an openid-provider.

    But the out-of-band extra security dawned on me – there already is a xmpp connection from mugshot client to server – but I wasn’t sure if it actually increased security, and I didn’t stop to think about it.

    Motivating that other people believes it does šŸ™‚

  11. Dirk Gently

    Nice to hear someone is thinking about this. I’ve heard of this kick and just can’t seem to understand why it’s catching on. The browser stores every password I possibly need and though OpenID would be super nice to joining a new site (heck it could even get rid of the signin form in alot of instances), I’m not about to trade security for it.

    FF3b4!??? hmmm.

  12. James Henstridge

    alex, steve: the image/text customisation method is already in use at sites like myopenid. Note however that the image needs to be associated with the computer (e.g. via a cookie with a large expiry time) rather than to anything the user types in. If the OP displayed these sorts of customisations during an authentication request at a new computer, then a rogue RP could do the same by proxying the page.

    Matthew, John: I am not too surprised to see that someone has done the out-of-band XMPP authentication solution (which is pretty cool!). I haven’t seen anything along the lines of the browser extension I outline, which I think could provide an interesting user experience.

  13. Kevin Turner

    Seatbelt, Sxipper, and Information Cards are browser extensions that can all integrate with some existing OPs today.

    The infocard WS-* goo isn’t so bad as you might think. There’s a BSD-licensed python implementation for self-issued infocards that you can refer to at

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