What this means is that if provided a valid username/password pair by Google, law enforcement agencies can gain access to an Android device that is protected with a screen unlock pattern. As I understand it, this assistance takes the form of two password changes: one to a new password that Google shares with law enforcement, followed by another that Google does not share with the police. This second password change takes place sometime after law enforcement agents have bypassed the screen unlock, which prevents the government from having ongoing access to new email messages and other Google account-protected content that would otherwise automatically sync to the device.

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It is my understanding, based on discussions with individuals who are familiar with Google’s law enforcement procedures, that the company will provide assistance to law enforcement agencies seeking to bypass screen unlock patterns, provided that the cops get the right kind of court order. The company insists on an anticipatory warrant, which the Supreme Court has defined as “a warrant based upon an affidavit showing probable cause that at some future time, but not presently, certain evidence of crime will be located at a specific place.”

Although a regular search warrant might be sufficient to authorize the police to search a laptop or other computer, the always-connected nature of smartphones means that they will continue to receive new email messages and other communications after they have been seized and searched by the police. It is my understanding that Google insists on an anticipatory warrant in order to cover emails or other communications that might sync during the period between when the phone is unlocked by the police and the completion of the imaging process (which is when the police copy all of the data off of the phone onto another storage medium).

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Of the three screen lock methods available on Android (pattern, PIN, password), Google only offers a username/password based bypass for the pattern lock. If you’d rather that the police not be able to gain access to your device this way (and are comfortable with the risk of losing your data if you are locked out of your phone), I recommend not using a pattern-based screen lock, and instead using a PIN or password.

However, it’s important to understand that while locking the screen of your device with a PIN or password is a good first step towards security, it is not sufficient to protect your data. Commercially available forensic analysis tools can be used to directly copy all data off of a device and onto external media. To prevent against such forensic imaging, it is important to encrypt data stored on a device.

Since version 3.0 (Honeycomb) of the OS, Android has included support for full disk encryption, but it is not enabled by default. If you want to keep your data safe, enabling this feature is a must.

Unfortunately, Android currently uses the same PIN or password for both the screen unlock and to decrypt the disk. This design decision makes it extremely likely that users will pick a short PIN or password, since they will probably have to enter their screen unlock dozens of time each day. Entering a 16-character password before making a phone call or obtaining GPS directions is too great of a usability burden to place on most users.

Using a shorter letter/number PIN or password might be good enough for a screen unlock, but disk encryption passwords must be much, much longer to be able to withstand brute force attacks. Case in point: A tool released at the Defcon hacker conference this summer can crack the disk encryption of Android devices that are protected with 4-6 digit numeric PINs in a matter of seconds.

Hopefully, Google’s engineers will at some point add new functionality to Android to let you use a different PIN/password for the screen unlock and full disk encryption. In the meantime, users who have rooted their device can download a third-party app that will allow you to choose a different (and hopefully much longer) password for disk encryption.