This is alarming, if true: according to a group of German security researchers at the University of Erlangen, if you put a locked, encrypted Android phone in the freezer for an hour and then quickly reboot it and plug it into a laptop, the memory will retain enough charge to stay decrypted, and can boot up into a custom OS that can recover the keys and boot the phone up with all the files available in the clear. The attack is called FROST: "Forensic Recovery Of Scrambled Telephones," and it requires a phone with an unlocked bootloader to work.
At the end of 2011, Google released version 4.0 of its Android operating system for smartphones. For the first time, Android smartphone owners were supplied with a disk encryption feature that transparently scrambles user partitions, thus protecting sensitive user information against targeted attacks that bypass screen locks. On the downside, scrambled telephones are a a nightmare for IT forensics and law enforcement, because once the power of a scrambled device is cut any chance other than bruteforce is lost to recover data.
We present FROST, a tool set that supports the forensic recovery of scrambled telephones. To this end we perform cold boot attacks against Android smartphones and retrieve disk encryption keys from RAM. We show that cold boot attacks against Android phones are generally possible for the first time, and we perform our attacks practically against Galaxy Nexus devices from Samsung. To break disk encryption, the bootloader must be unlocked before the attack because scrambled user partitions are wiped during unlocking. However, we show that cold boot attacks are more generic and allow to retrieve sensitive information, such as contact lists, visited web sites, and photos, directly from RAM, even though the bootloader is locked.