Since we began work on an extensions system for Chromium, we've received a lot of positive feedback. While the system is not yet complete, we've noticed that a lot of you have started creating and installing extensions for daily use. This is really encouraging, and it motivates us to quickly finish things up, to enable extensions by default on all Google Chrome releases.

If you're using extensions now, you should keep in mind that they are powerful software. Extensions integrate with your browser, so they can access and change everything that happens in it. For example, the same technology that enables an extension to periodically check the number of messages in your Gmail inbox could also be used to read all your personal mail and tweet it to your mom! This can happen because of malicious intent or simply because of a bug.

To help protect your experience when using extensions, we recently enabled auto-update for extensions on the dev channel release. Like Chrome's auto-update mechanism, extensions will be updated using the Omaha protocol, giving developers the ability to push out bug fixes and new features rapidly to users of their extensions. This is an important step towards a v1 release of extensions for all users, so we're pretty excited.

In addition, when we turn the extension system on, we plan to offer a gallery with ratings and comments that you can use to judge whether you want to install a particular extension. We will also have processes in place that, combined with reports from users, should help limit the number of malicious extensions that get uploaded and distributed to users. These processes will include removal of extensions that we have reason to believe are malicious. Until these things are in place and the extension system is officially launched, we recommend that you only install extensions that you built yourself.

Posted by Aaron Boodman, Software Engineer

We have just started using a new compression algorithm called Courgette to make Google Chrome updates small.

We have built Google Chrome to address multiple factors that affect browser security. One of the pillars of our approach is to keep the software up to date, so we push out updates to Google Chrome fairly regularly. On the stable channel these are mainly security bug fixes, but the updates are more adventurous and numerous on developer channel.

It is an anathema to us to push out a whole new 10MB update to give you a ten line security fix. We want smaller updates because it narrows the window of vulnerability. If the update is a tenth of the size, we can push ten times as many per unit of bandwidth. We have enough users that this means more users will be protected earlier. A secondary benefit is that a smaller update will work better for users who don't have great connectivity.

Rather then push put a whole new 10MB update, we send out a diff that takes the previous version of Google Chrome and generates the new version. We tried several binary diff algorithms and have been using bsdiff up until now. We are big fans of bsdiff - it is small and worked better than anything else we tried.

But bsdiff was still producing diffs that were bigger than we felt were necessary. So we wrote a new diff algorithm that knows more about the kind of data we are pushing - large files containing compiled executables. Here are the sizes for the recent 190.1->190.4 update on the developer channel:

• Full update: 10,385,920 bytes
• bsdiff update: 704,512 bytes
• Courgette update: 78,848 bytes

The small size in combination with Google Chrome's silent update means we can update as often as necessary to keep users safe.

More information on how Courgette works can be found here.

Posted by Stephen Adams, Software Engineer