Personal by Design: How we built Opera Sync

What is Firefox Sync and precisely why would you use it

That shopping rabbit hole a person started on your laptop this morning? Pick-up where you left off on your cell phone tonight. That dinner recipe a person discovered at lunchtime? Open it on your own kitchen tablet, instantly. Connect your individual devices, securely. – Opera Sync

Firefox Sync lets you share your own bookmarks, browsing history, passwords along with other browser data between different gadgets, and deliver tabs from one gadget to another. It’ s a feature that will millions of our users take advantage of in order to streamline their lives and how these people interact with the web.

Yet on an Internet where sharing your computer data with a provider is the norm, good it’ s important to highlight the particular privacy aspects of Firefox Sync.

Firefox Sync by default protects all of your synced data so Mozilla can’ t read it. We constructed Sync this way because we place user privacy first. In this post, we all take a closer look at some of the specialized design choices we made plus why.

When creating a browser and implementing a synchronize service, we think it’ s crucial that you look at what one might contact ‘ Total Cost of Ownership’.   Not just what users get from a function, but what they quit in exchange for simplicity of use.

We believe that by causing the right choices to protect your personal privacy, we’ ve also lowered the particular barrier to trying out Sync. Once you sign up and choose a strong passphrase, your data is protected from each attackers and from Mozilla, so that you can try out Sync without worry. Give it a shot, it’ s right up there in the menus bar!

Sign in to Sync Button within the Firefox Menu

Why Firefox Sync is safe

Encryption allows one to guard data so that it is entirely unreadable without the key used to encrypt this. The math behind encryption is definitely strong, has been tested for decades, each government in the world uses it to safeguard its most valuable secrets.

The hard part of encryption is that essential. What key do you encrypt along with, where does it come from, where could it be stored, and how does it move among places? Lots of cloud providers state they encrypt your data, and they perform. But they also have the key! While the encryption is not meaningless, it is a small determine, and does not protect the data against the many concerning threats.

The particular encryption key is the essential component. The service provider must never receive this – even temporarily – plus must never know it. When you sign into the Firefox Account, you enter the username and passphrase, which are delivered to the server. How is it that people can claim to never know your encryption key if that’ s whatever you ever provide us?   The difference is in how we handle your own passphrase.

An average login flow for an internet service would be to send your username and passphrase up to the server, where they hash it, compare it to a saved hash, and if correct, the machine sends you your data. ( Hashing refers to the experience of converting passwords into unreadable strings of characters impossible in order to revert. )

Typical Web Provider Sign in Flow

The crux of the difference in how we created Firefox Accounts, and Firefox Synchronize (our underlying syncing service), is that you simply never send us your passphrase. We transform your passphrase on your computer in to two different, unrelated values. Along with one value, you cannot derive another. We send an authentication expression, derived from your passphrase, to the machine as the password-equivalent. And the encryption essential derived from your passphrase never simply leaves your computer.

Firefox Sync Login Flow

Interested in the technical information?   We use 1000 models of PBKDF2 to derive your own passphrase into the authentication token. Within the server, we additionally hash this particular token with scrypt (parameters N=65536, r=8, p=1) to make sure our data source of authentication tokens is even more complicated to crack.

All of us derive your passphrase into a good encryption key using the same multitude of rounds of PBKDF2. It is domain-separated from your authentication token by using HKDF with separate info values. We all use this key to unwrap a good encryption key (which you created during setup and which we all never see unwrapped), and that encryption key is used to protect your data.   We use the key to encrypt your data using AES-256 in CBC mode, protected with an HMAC.

This cryptographic design will be solid – but the constants have to be updated. One thousand rounds of PBKDF can be improved, and we intend to do this in the future ( Annoy 1320222 ). This symbol is only ever sent over a HTTPS connection (with preloaded HPKP pins) and is not stored, so when we all initially developed this and required to support low-power, low-resources devices, the trade-off was made. AES-CBC + HMAC is acceptable – it might be nice to upgrade this for an authenticated mode sometime in the future.

Other approaches

This isn’ t the only method of building a browser sync feature. You can find at least three other options:

Option 1: Share your data with all the browser maker

In this particular approach, the browser maker can read your data, and use it to provide solutions to you. For example ,   when you synchronize your browser history in Chromium it will automatically go into your Web & Application Activity unless you’ ve changed the default configurations. As Google Chrome Help explains, “ Your activity may be used to personalize your own experience on other Google items, like Search or ads. For instance , you may see a news story recommended inside your feed based on your Chrome background. ”

Option two: Use a separate password for sign-in and encryption

We all developed Firefox Sync to be as effortless to use as possible, so we designed this from the ground up to derive a good authentication token and an encryption key – and we never view the passphrase or the encryption key. A single cannot safely derive an encryption key from a passphrase if the passphrase is sent to the server.

One could, however , add a 2nd passphrase that is never sent to the particular server, and encrypt the data making use of that. Chrome provides this like a non-default option. You can sign in order to sync with your Google Account qualifications; but you choose a separate passphrase in order to encrypt your data. It’ s essential you choose a separate passphrase though.

All-in-all, we don’ to care for the design that requires a second passphrase. This approach is confusing to customers. It’ s very easy to choose the exact same (or similar) passphrase and negate the security of the design. It’ t hard to determine which is more complicated: to require a second passphrase in order to make it optional! Making it optional indicates it will be used very rarely.   We don’ t believe customers should have to opt-in to personal privacy.

Option 3: Guide key synchronization

The main element (pun intended) to auditing the cryptographic design is to ask about the main element: “ Where would it come from? Where does it go? ” With the Firefox Synchronize design, you enter a passphrase of your choosing and it is used to obtain an encryption key that never ever leaves your computer.

An additional option for Sync is to remove consumer choice, and provide a passphrase for a person (that never leaves your computer). This passphrase would be secure plus unguessable – which is an advantage, however it would be near-impossible to remember – that is a disadvantage.

When you want to include a new device to sync in order to, you’ d need your current device nearby in order to manually look at and type the passphrase in to the new device. (You could also check out a QR code if your brand new device has a camera).

Other Browsers

General, Sync works the way it does due to the fact we feel it’ s the very best design choice. Options 1 plus 2 don’ t provide comprehensive user privacy protections by default. Choice 3 results in lower user adopting and thus reduces the number of people we are able to help (more on this below).

As noted above, Stainless implements Option 1 by default, meaning unless you change the configurations before you enable sync , Search engines will see all of your browsing history as well as other data, and use it to market services for you. Chrome also implements Option two as an opt-in feature.

Both Opera and Vivaldi stick to Chrome’ s lead, implementing Choice 1 by default and Option two as an opt-in feature.

Brave, also a privacy-focused browser, provides implemented Option 3. And, actually Firefox also implemented a form of Option several in its original Sync Protocol, yet we changed our design within April 2014 (Firefox 29) according to user feedback. For example , our primary design (and Brave’ s present design) makes it much harder in order to regain access to your data if you drop your device or it will get stolen. Passwords or passphrases create that experience substantially easier for the typical user, and significantly increased Synchronize adoption by users.

Brave’ s sync protocol has its own interesting wrinkles. One distinct without is that you can’ t change your passphrase, if it were to be stolen simply by malware. Another interesting wrinkle is the fact that Brave does not keep track of how many or even what types of devices you have. This is a refined security trade-off: having less details about the user is always desirable… The downside is the fact that Brave can’ t allow you to identify when a new device begins getting your sync data or permit you to deauthorize it. We respect Brave’ s decision. In Firefox, nevertheless , we have chosen to provide this extra security feature for users (at the cost of knowing more about their devices).


We designed Firefox Sync to safeguard your data – by default – therefore Mozilla can’ t read this. We built it this way – despite trade-offs that make development plus offering features more difficult – since we put user privacy 1st. At Mozilla, this priority is really a core part of our mission in order to “ ensure the Internet is a worldwide public resource… where individuals may shape their own experience and are stimulated, safe and independent. ”

You are able to use one to suppose the other, but only when you choose a weak password.

  You can get more details in the full protocol specification or by following the code starting at this point . There are a few details we have omitted in order to simplify this blog post, including the distinction between kA and kB tips, and application-specific subkeys.

Server hashing code is located here .

The encryption code can be seen here . Section “ Use your Chromium history to personalize Google”

  Stainless 71 says “ For additional security, Google Chrome will encrypt your own data” and describes these two choices as “ Encrypt synced security passwords with your Google username and password” and “ Encrypt synced information with your own synchronize passphrase ”.   Regardless of this wording, only the sync passphrase choice protects your data from Google.

  Among the original engineers of Sync offers written 2 blog posts about the changeover to the new sync protocol, plus why we did it. If you’ re interested in the usability facets of cryptography, we highly recommend you look at them to see what we learned.

  Read more about Brave sync on Brave’ s Style page .

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