As forensic examiners, some of the last things we want to hear are “encryption” and “enabled” in the same sentence, however that’s what has been happening with the current line of Android devices. Starting with Android 3.0, devices have been shipping with the ability for the user to enable full device encryption. Fortunately for the forensic community, there are individuals steadfast to find a way to break that encryption – and have already proven how to do so. Two such researchers – Thomas Cannon and Seyton Bradford – have demonstrated successful brute force attacks against Android encryption. Thomas detailed their findings at DEF CON 2012 in his presentation "Into the Droid – Gaining Access to User Data"…He discusses that the encryption uses standard Linux dm-crypt, incorporated in Android devices running version 3.0 and newer, and uses the same password to encrypt and decrypt data as is used to unlock or log in to the device. So while the encryption is generally considered strong, users default to using short or easy-to-type passwords and pins to protect their device and enable the encryption.
Cannon and Bradford have created a brute force tool that is able extract the required information from the encrypted volume, then launch a brute force attack automatically. The tool can brute force pin locks on Android devices running OS 4.0 and higher. They’ve incorporated that tool into the F/OSS Santoku Linux, which you can download at www.santoku-linux.com.
Cannon did recommend changes in the way the encryption is implemented to improve the encryption and make it much more difficult to crack. He recommended incorporating a much stronger boot-time password and an easier-to-use password when simply unlocking a device.
You can see the slides from his full presentation at https://viaforensics.com/mobile-security-category/droid-gaining-access-android-user-data.html.