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If it becomes the case that my phone is stolen, I would like to make it as difficult as possible, if not impossible, for my data to be accessed without my permission.

I understand that Android has the ability to perform a full disk encryption on my phone. However, I also understand that the disk is decrypted on boot. Which means once the phone has successfully booted, the encryption is no longer applicable.

Personally, I tend to keep my phone booted at all times for convenience reasons. This seems to imply that my phone will therefore be decrypted at all times. Given this situation, are there still any benefits to encrypting my Phone? Additionally, would encryption help me at all in the case of theft? If not, are there any alternatives to protecting my data from theft?

  • It's likely that if your phone got stolen, the thief would either turn it off or enable aeroplane mode to stop you being able to remotely wipe it; if it is turned off (or e.g. the battery runs out), encryption will help to keep your data safe. – Josh Aug 6 '16 at 15:11
  • @Josh If the thief simply enabled aeroplane mode without turning off the phone, do I understand correctly that I am still able to rely on encryption to keep my data safe? Or would I have to hope the battery runs out in this case? – Zsw Aug 6 '16 at 21:08
  • The thief would still need your password to access your data, even though that's not due to encryption. Enabling encryption doesn't really have any downsides, even though it only helps under a few circumstances. – Josh Aug 6 '16 at 21:51
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As long as your phone is turned on, no matter if it is locked, in airplane mode, etc., the data partition remains indeed decrypted and therefore, as you say, you do not really take advantage of disk encryption.

Even worse: when I say that the partition is "decrypted", concretely this means that the data encryption key is present somewhere in your phone memory. If the data on your phone is valuable enough (eg. has any value for corporate or governmental adversaries), there are techniques allowing an advanced attacker to dump this memory, get this encryption key, and access your data no matter if your phone was locked in the first place.

The good news is that there are applications allowing you to shutdown or reboot the phone after a few unsuccessful unlock attempts. Concretely, this means that after let's say 5 wrong unlock attempts, the phone will shutdown/reboot, effectively dropping the encryption key from memory, leaving the attacker no way to access your data without finding your encryption key.

Moreover, I attract your attention the fact that Google put an arbitrary limitation in Android requiring the end-users to use the same password for decryption and unlocking. If you have rooted your device, there are ways to use a strong and complex password for disk encryption and a quick to input unlock PIN. Be aware that using short/easy passwords or a PIN for encryption essentially annihilates any advantage brought by encryption since they would be breakable using dictionary or brute-force attacks.

  • +1 and using the same key is Achilles heel – beeshyams Aug 7 '16 at 10:31
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Locking you phone will enable encryption.

On boot you are required to use your encryption pin/password to decrypt. After boot decryption and later lock (like in your case when your phone is always on) you can unlock with a fingerprint if enabled. This is a weakness (because fingerprints can be spoofed).

Disable the Marshmallow fingerprint option and stick to a very strong alphanumeric password. Then you data will be safe any time you phone is locked (even if it is not turned off).

  • Alphanumeric does not lead to strong passwords.. see Short complex password, or long dictionary passphrase? – beeshyams Aug 6 '16 at 10:51
  • "Locking you phone will enable encryption.": can you elaborate on this one or provide any sources? As it is currently stated, it seems to infer that the phone requires you to to input the key in order to decrypt the data, which is not true otherwise application would not be able to run in the background. The fact that the lock key is also used for encryption is an arbitrary limitation imposed by Google, technically they do not need to be the same and there are some workarounds allowing the user to use different keys for encryption and device locking. – WhiteWinterWolf Aug 7 '16 at 10:04

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