A new feature in Google's Chrome browser will warn you if your username and password matches a known combination in a security breach every time you type credentials into any website.

This credential check is "gradually rolling out for everyone signed into Chrome" as part of the Safe Browsing option, according to the announcement.

The potential worry here is that sending your credentials to Google for checking could itself be a security risk. The technology used was announced nine months ago, when the Password Checkup extension was introduced. At the time it was described as an "early experiment". The way it works is as follows:

Google maintains a database of breached usernames and passwords, hashed and encrypted. In other words, the username/password combinations are not stored, only the encrypted hash. When you type in your credentials, the browser sends a hashed and encrypted copy of the credentials to Google, where the key used for encryption is private to the user. In addition, it sends a "hash prefix" of the account details, not the full details. Google searches the breach database for all credentials matching the hash prefix and sends the results back to the browser. These are encrypted with a key known only to Google. In addition, Google encrypts your credentials with this same key – so it is now doubly encrypted. The final check is local. Chrome decrypts the credentials using your private key, yielding a copy encrypted only with Google's key. This is then compared to the values in the database. If a match is found, an alert is raised.

The process by which Google checks credentials against a database of breached usernames and passwords (Click to enlarge)

The idea is that your credentials are never sent to Google in a form it can read, and that details of other people's breached credentials are never sent to you in a form you can read. The procedure, we are told, "reflects the work of a large group of Google engineers and research scientists".

Even though users may still feel uncomfortable enabling this kind of check, the risks are likely lower than that of being unaware that your credentials have been stolen. The bigger snag, perhaps, is that you have to sign into Chrome with all that implies in terms of giving the data-grabbing giant more information about your digital life.

In addition, Google says it is improving its phishing site protection, with 30 per cent more cases being spotted. A further protection is that if you use Chrome's password manager, you will be alerted if you enter credentials stored there into a suspected phishing site.

What about if someone else signs into Chrome on a shared computer, and you inadvertently save your password into someone else's profile? If this can happen you probably already have some potential security issues to worry about, but Google is trying to make it less likely by a more prominent indication of the current profile. ®