Security Analysis of Android Factory Resets
With hundreds of millions of devices expected to be traded by 20181 , flaws in smartphone sanitisation functions could be a serious problem. Trade press reports2 have already raised doubts about the effectiveness of Android “Factory Reset”, but this paper presents the first comprehensive study of the issue. We study the implementation of Factory Reset on 21 Android smartphones from 5 vendors running Android versions v2.3.x to v4.3. We estimate that up to 500 million devices may not properly sanitise their data partition where credentials and other sensitive data are stored, and up to 630M may not properly sanitise the internal SD card where multimedia files are generally saved. We found we could recover Google credentials on all devices presenting a flawed Factory Reset. Full-disk encryption has the potential to mitigate the problem, but we found that a flawed Factory Reset leaves behind enough data for the encryption key to be recovered. We discuss practical improvements for Google and vendors to mitigate these risks in the future.