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Are there any off-the-shelf options for securing the contents of an SD card so that files written by apps writing to SD are encrypted? If so, what is the best option?

I'm looking for something for all apps. I would strongly prefer to do it without rooting.

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The samsung galaxy S has the ability to support a non standard filesystems. Hacking a filesystem together with encryption should be possible but probably takes a lot of time and as far as I know isnt available off the shelf atm. – Barfieldmv Oct 6 '10 at 8:29
    
SecretVaultPro may be headed in the right direction. It mounts an encrypted file as folder which could be used by apps where data is save to a user-selected folder. I'd prefer to secure the entire card for app data that the user can't select where to store on the SD card. – BrianCooksey Oct 12 '10 at 3:02
    
The Linux kernel uses the dm-crypt subsystem for transparent on-the-fly encryption; I believe app2sd uses dm-crypt, so at least the Linux kernel of Froyo should come with dm-crypt. You might want to look at how to configure vold to mount dm-crypt filesystems. – Lie Ryan Jan 6 '11 at 15:38
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Ice Cream Sandwich has an "Encrypt Phone" option in settings -> Security, but it's not clear if this includes the SD card, or just the internal memory of the phone. – rjmunro Dec 19 '11 at 18:36
up vote 1 down vote accepted

Android 6.0 (Marshmallow) has a feature called "adoptable storage", which allows the external SD card to be treated as if it were internal storage. When this is done, everything on the card is encrypted.

More details: https://source.android.com/devices/storage/adoptable.html

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For anyone who stumbles upon this topic. Motorola seems to offer a solution for full storage encryption of internal and sd card.

Link: https://motorola-enterprise.custhelp.com/app/answers/detail/a_id/57094

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Sounds like just what the poster's after. It isn't available yet, but should be in early 2011. It will be specific to Motorola Android devices. – GAThrawn Jan 6 '11 at 16:44
    
Here's what I found on that subject: android.stackexchange.com/questions/13174/… – galets Sep 20 '11 at 22:02
    
The page says it's no longer available. – Dan Dascalescu Jul 6 '14 at 1:02

As of July 2014, I've found the following options for SD card encryption:

  • Boxcryptor - not open source; developed by German company; supports sync with cloud storage; unclear if they've received a backdoor request
  • cryptonite - open source; supports mounting TrueCrypt volumes; no backdoor request yet
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