seanmonstar

Jun 3 2014

Firefox Accounts OAuth Explorations

As we build Firefox Accounts, a key part to the whole experience is allowing a user to divvy out information to apps. We’ll be doing so with an OAuthish experience.

OAuth2

The first obvious place to look was the OAuth2 spec. We’ve based most of our experience on this model. Using the spec, a flow for an imaginary website Cuddly Foxes would like this:

  1. Cuddly Foxes would register with our oauth server, supplying a redirect_uri, and we’ll give you back a client_id and client_secret.
  2. Cuddly Foxes will make their login button redirect the browser to our server, passing the client_id, a random state, and desired scope, such as profile:email.
  3. Our server will show the user some information about who is asking and what info is being asked for, and ask them to confirm. They can uncheck any scopes they don’t want to give out.
  4. The server will generate a code representing the current auth request, and redirect back to Cuddly Foxes’ redirect_uri, including the random state and a code parameter.
  5. Cuddly Foxes first verifies that the returned state is one they sent, and then sends the code back to our server, along with the client_secret they received at registration.
  6. Our server will verify the client_secret matches what is associated with the code, and then will send back a token and the scopes the token has been approved for.
  7. Cuddly Foxes would then use that token whenever asking for the user’s email address, from our profile server, since that’s the scope that was asked for.

So far, standard OAuth2. The client_secret, code, and token are 32-byte random hex strings, and we store a hash of them in our database, reducing the damage done if it gets compromised. Now, let’s add in another service provider: FoxCoin, the newest hotness in privacy-respecting crypto-currency. Cuddly Foxes wants to set up a recurring subscription to send new Foxes every month to users.

That means that they ask our OAuth server for a token with scopes ‘profile:email’ and ‘foxcoin’. With the token in hand, they ask the Profile server for the user’s email, providing said token as proof that they can receive profile information, and they receive it. But! The profile server just received a token that it can use to access the user’s FoxCoin information, acting as Cuddly Foxes. Yikes!

Of course, we can assume the Profile server wouldn’t do anything so nefarious, but having that power is still dangerous. And imagine as we add in more 3rd-party attached services, which inherently are less trustworthy. Additionally, with the recent discovery in OpenSSL, we don’t want to trust TLS alone to protect against sniffing the data as it passes. So, passing around a Bearer token in plain text is unacceptable.1

OAuth2 HMAC

The next step was to consider using a secret token to sign a request, so that the original token is never revealed. This has been excellently explored already by the Hawk scheme. The short of it is that 2 parties who share a secret can sign the request with an HMAC, proving that the request and it’s payload came from one of them. The receiver just computes the same HMAC, and compares signatures. The original secret is never leaked to anyone. Many cookies were had by all.

Adapting that to our OAuth flow, we would return a random token like before, and Cuddly Foxes would use it to generate a Hawk authorization header, and send it to our Profile server. The Profile server, not knowing the secret token, would tediously need to send the various bits of the request making up the signature, plus the authorization header, to our OAuth server. The OAuth server would look up the secret token, compute the HMAC, and return whether it was valid.2

This is an improvement, since the secret token is never visible on the wire, nor does the Profile server receive it. However, a downside is that for this to work, the OAuth server needs to keep the original secret token in plain text. Before, we were keeping a hashed copy of it, which meant that a snapshot of our database would not reveal everyone’s secret tokens. We didn’t like this disadvantage, and so continued to explore.

OAuth with Public Key Signing

We wanted to keep the request signature, since that doesn’t leak the secret to anyone else, while not having to retain the original secret ourselves. It turns out, there is a technology that does exactly this: asymmetric public key cryptography. However, using RSA or DSA keys has its problems: signing and verifying is slow, generating new keys is slow, and sending public keys with each request is a lot of bytes. That’s when my colleague Brian Warner brought up the newest hotness: elliptic curve public keys. Particularly, Ed25519. It’s super fast to create keys, signing and verifying are fast, and public keys are 32-byte strings. The secret keys are likewise 32 bytes, and completely random, so brute force guessing takes longer than any human could ever wait.

So what’s that look like for Firefox Accounts? The updated flow looks like this:

  1. Stays the same.
  2. Stays the same.
  3. Stays the same.
  4. Stays the same.
  5. Cuddly Foxes first verifies that the returned state is one they sent. They generate a new ed25519 keypair for this user+scope, and then sends the pubkey, the code, and the client_secret they received at registration to the server. This registers that public key with our OAuth service.
  6. Our server will verify the client_secret matches what is associated with the code, save the public key, and return the scopes that have been approved.
  7. Cuddly Foxes would then use that private key to sign a request asking for the user’s email address, from our Profile server, since that’s the scope that was asked for.

Afterwards, the Profile server can verify the signature by itself, since it contains the public key in it. This removes the need for each attached service to figure out what parts of a request to forward to the OAuth server. It also means that all service providers will handle their own hash computing, reducing strain on our OAuth server. Once a signature is verified, the Profile server can simply ask the OAuth server what scopes are provided for that public key, and then act accordingly.

Here’s an example request:

HTTP/1.1
GET /v1/email
Host: profile.accounts.firefox.com
Authorization: 'Gryphon pubkey="461d65b867d02ddf7f0d0bf3c2746c823605dec5e9f221ca7f451113fcddaf9f", ts="1400641081466", nonce="992022dd", sig="f1pIEz5y9sN6Bsc00iIy9YcEBFRLqCAtkTspvqQPb4FKUIMwrXxXiqBYXJbdAXc0FM1R6H9bdD+Pkx8klFUNCA=="'

The signature proves that the request originated from the owner of the pubkey, and the payload hasn’t been modified.

There be Gryphons

The authorization scheme in the example above is “Gryphon”. It was partly influenced by Hawk, but felt like a more powerful version. Mozilla has a habit of naming projects after mythological creatures. Most importantly, gryphons “are known for guarding treasures or priceless possessions.” Certainly, user data is a priceless possession.

Gryphon isn’t complete. It’s currently in a proof-of-concept stage. There’s a working branch of our oauth server using it. However, we’d like to get more eyeballs on it before feeling confident about shipping. Are there missing pain points, or use cases not covered? Send me a comment, or write up some analysis and send me the link, or come chat in #fxa, or anything, really.


  1. This issue doesn’t appear in all OAuth models. The issue comes from us having multiple mutually-distrusting services, being gated by our OAuth server. We plan to allow clients, such as your website, request data from a service provider, run by your digital neighbor, about a user.

    In most cases, all the data comes from the same entity that runs the OAuth server, and so there’s no worry that it will mishandle the power it gives itself. 

  2. A downside here is that this means the OAuth server is doing all hashing for all requests, which puts a requirement on our OAuth server using more resources. 

Mar 25 2014

Your Password is Insecure

We know that you should have a unique, sufficiently-long, sufficiently-randomized password for every property that requires one. We also know that if you most likely don’t do this whatsoever. There’s no way we’re going to change users’ habits. So this is the reason why we need to get rid of passwords.1

You may think the danger exists with someone guessing your password at your bank, or your email account. Instead, those websites have teams of professionals who spend their whole working day keeping out hackers. That’s not where the danger starts. The danger starts at a tiny e-commerce site, or webforum, or other small-scale site. Some site where you’d think “I don’t care if this account is stolen.” Those are the dangerous sites. Even if you think your password is a pretty good one, because it doesn’t contain any personalized information, and looks like gibberish: if you use the same password, then your password is as weak as the weakest site you use it at.

What really happens: a mom-and-pop shop that sells honey decides to sell more via a website, and has you log in to remember your shipping address. They’re not security experts. They didn’t hire any either. A hacker aims for sites like those. The hacker only has to get passed the minimal security of Honey Buns, to find a list of e-mails and passwords. Maybe the passwords aren’t even hashed; they’re just sitting there in plain text. You shouldn’t be worried that the hacker can ship an insane amount of honey to your house. They wouldn’t bother. Instead, they will take that list, and try each e-mail/password combo on important sites: Wells Fargo, Bank of America, Gmail, Paypal, etc. You used the same email and password on one of those sites as you did with Honey Buns? Then the hacker has just successfully logged in as you, and it mostly looks like a normal login. They then transfer money to their account, and carry on.2


  1. I’ve been explaining this to anyone who has asked me about Persona and passwords, and figured it’d be nice to have it in a linkable quotable location. 

  2. Of course, those sites try to protect against this too. They might notice the IP address is from a completely different part of the world. And they might prevent dangerous actions from that IP until you’ve confirmed another e-mail challenge. But the point still stands. 

Aug 8 2013

Gmail Bridge for Persona

Since shifting to the Identity team last year, I’ve been working hard on making Persona a true solution to the login problem of the web. As I said then:

If we do our job right, eventually when my friends ask me what I do, I can say: I helped make it so you no longer need to use passwords everywhere. I helped make your online identity more secure. I helped make signing into the Internet awesomer.

We’re getting closer.

What is the Gmail Bridge?

Today, we’re announcing to the world that our Gmail Identity Bridge is online. Excuse me. What? No, I’m fine. It’s alright, it’s actually quite simple.

The way Persona normally works, after checking to see if your email provider natively supports the protocol, is that Persona will fallback to what we call a secondary provider. This is the point where most users end up creating a password for Persona, and then going to their email to verify to us that they really own their email address. If the email provider did support the protocol, they would get sent over to them to authenticate, and we’d step out of the way.

So, we made an Identity Bridge that we host, and uses Google’s OpenID endpoint to verify the user. The experience is pretty much exactly what it should feel like if there was native support from Google.

Why this matters

With both Gmail and Yahoo bridges online, over half of all users are just a couple clicks away from logging in with Persona.

So how does this affect you? If you have a website that has user accounts, you can switch to using Persona as your authentication system. In most cases, it should be a better experience for your users, and easier for you.

If you don’t have a website, you can still help. Find a website you log in to frequently, and ask them to implement Persona. Tell them about this new bridging. Push for the change.

Soon, everyone will notice: we made signing into the Internet awesomer.

Apr 10 2013
Sep 27 2012
Jul 20 2012

Moved to Identity

I’ve been working at Mozilla on the same project for a year and a half now, and it’s time for some change.

I spent that time working on Add-on Builder, taking it from prototype to launched product. With it being largely a single-page app, I refined a lot of my views on organizing and structure large amounts of JavaScript. I formed that new knowledge into Shipyard, and got to work on that and improve it much the first half of this year.

I’m proud of how easy it is to start writing a new add-on for Firefox, test it, and publish it to addons.mozilla.org; all entirely in the browser.

I started thinking I wanted to do more, though. By more, I mean affect more people on the Internet. As various friends would ask me what I do at Mozilla, I would tell them I make a tool for developers to more easily make add-ons, that my friends might use. Except many don’t use add-ons, or even Firefox. I realized I wanted to make something that normal people would use. What is something on the Internet that normal people use, and currently sucks? Logging in.

Mozilla’s Identity team has been working on a new system to greatly improve signing into the Internet. I’ve been watching it since they announced it, and now I get to help create and improve on the new Persona project.

If we do our job right, eventually when my friends ask me what I do, I can say: I helped make it so you no longer need to use passwords everywhere. I helped make your online identity more secure. I helped make signing into the Internet awesomer.

Jul 20 2011