Google Online Security Blog: Using a built-in FIDO authenticator on latest-generation Chromebooks

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Using a built-in FIDO authenticator on latest-generation Chromebooks

November 19, 2019

Posted by Christiaan Brand, Product Manager, Google Cloud

announcedDeviceSecondFactorAuthentication

Main use cases
FIDO technology aims to solve three separate use cases for relying parties (or otherwise referred to as Internet services) by helping to:

Prevent phishing during initial login to a service on a new device;
Reverify a user’s identity to a service on a device on which they’ve already logged in to;
Confirm that the device a user is connecting from is still the original device where they logged in from previously. This is typically needed in the enterprise.

Security-savvy professionals may interpret the third use case as a special instance of use case #2. However, there are some differences, which we break down a bit further below:

In case #2, the problem that FIDO technology tries to solve is re-verifying a user’s identity by unlocking a private key stored on the device.
In case #3, FIDO technology helps to determine whether a previously created key is still available on the original device without any proof of who the user is.

How use case #1 works: Roaming security keys

Because the whole premise of this use case is one in which the user logs in on a brand new device they’ve never authenticated before, this requires the user to have a FIDO security key (removeable, cross-platform, or a roaming authenticator). By this definition, a built-in FIDO authenticator on Chrome OS devices would not be able to satisfy this requirement, because it would not be able to help verify the user’s identity without being set up previously. Upon initial log-in, the user’s identity is verified together with the presence of a security key (such as Google’s Titan Security Key) previously tied to their account.

Titan Security Keys

Once the user is successfully logged in, trust is conferred from the security key to the device on which the user is logging on, usually by placing a cookie or other token on the device in order for the relying party to “remember” that the user already performed a second factor authenticator on this device. Once this step is completed, it is no longer necessary to require a physical second factor on this device because the presence of the cookie signals to the relying party that this device is to be trusted.

Optionally, some services might require the user to still periodically verify that it’s the correct user in front of the already recognized device (for example, particularly sensitive and regulated services such as financial services companies). In almost all cases, it shouldn’t be necessary for the user to also-in addition to providing their knowledge factor (such as a password) - re-present their second factor when re-authenticating as they’ve already done that during initial bootstrapping.

Note that on Chrome OS devices, your data is encrypted when you’re not logged on, which further protects your data against malicious access.
How use case #2 works: Re-authentication recently enabled
Additionally, there are security benefits to this particular solution, as the relying party doesn’t only have to trust a previously issued cookie, but can now both verify that the right user is present (by means of a biometric) and that a particular private key is available on this particular device. Sometimes this promise is made based on key material stored in hardware (e.g. Titan security in Pixel Slate), which can be a strong indicator that the relying party is interacting with the right user on the right device.
How use case #3 works: Built-in device authenticator

Pixel Slate devices are built with hardware-based Titan security

We still highly recommend users to have a primary FIDO security key, such as Titan Security Key or an Android phone. This should be used in conjunction with a “FIDO re-authentication” policy, which is supported by G Suite.

Enabling the built-in FIDO authenticator in the Google Admin console

Supported Chromebooks
Starting with Chrome 76, most latest-generation Chromebooks gained the option to enable a built-in FIDO authenticator backed by hardware-based Titan security. To see if your Chromebook can be enabled with this capability, you can navigate to chrome://system and check the “tpm-version” entry. If “vendor” equals “43524f53”, then your Chromebook is backed by Titan security.

Navigating to chrome://system on your Chromebook

Summary
In summary, we believe that this new enhancement can provide value to enterprise organizations that want to confirm that the device a user is connecting from is still the original device from which a user logged in from in the past. Most users, however, should be using roaming FIDO security keys, such as Titan Security Key, their Android phone, or security keys from other vendors, in order to avoid account lockouts.