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I bought a new USB Hard Drive that I want to use as a back up for my Linux (Ubuntu 14.04 LTS at the moment) and my Mac Mini (running Mac OS X 10.9). I can do this perfectly at the moment, but I want to be able to encrypt the files that are on the hard drive. I know I can do this if the hard drive was to be used by either machine exclusively, but unfortunately it’s used by more than one machine running two different operating systems.

Is it possible to do this? I’d prefer a whole drive encryption, but if an “encrypted folder” solution is the only way—or is the better way—then I’d like to know how to do it.

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  • Does the backup itself offer encryption?
    – JDługosz
    Apr 1, 2015 at 0:20
  • No the backup device has no encryption Apr 1, 2015 at 0:50
  • I mean the backup software. E.g. Clonezilla
    – JDługosz
    Apr 1, 2015 at 1:01

3 Answers 3

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The program Truecrypt is commonly used for this purpose and is cross-platform. There was a famous announcement about it being discontinued with a suggestion to use (windows-specific) ntfs encryption. I've not looked into the status lately, but use a version from before the hiatus. Meanwhile, a peer-review code review and audit was already underway, so it may be "back" under a new team.

In my experience, formatting the USB with FAT32 and then using a container file, as opposed to giving a raw partition to Truecrypt, is portable and less cranky to get working right. That also makes it trivial to encrypt just part of the drive.

Some USB flash drives are sold with encryption as a feature, but the fine print suggests that it's just a bundled program like that. Some rare units do have drive-level encryption inside the drive itself.

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  • The audit found many problems with the code base and TrueCrypt itself is don't. Finished. No more. OTOH, many forks of it came out to continue its legacy with a few promising to fix the problems (bugs?)
    – Cole Tobin
    Apr 1, 2015 at 2:10
  • 1
    I read "no evidence of backdoors or malicious code". Where did you see that the audit found many problems? Agreed, if I didn't already have it, I'd consider the newer forks rather than an old version, but the old brand name is the starting point for searching.
    – JDługosz
    Apr 1, 2015 at 4:06
  • Keep in mind that FAT32 has a 4GB filesize limit per-file; this may have impact if you decide to format your partition FAT32 and then use a container file.
    – Suchipi
    Apr 1, 2015 at 6:17
  • Good point. Not too long ago that was not an issue. Today you can have exFat, the default on larger flash media, which does not have that limit.
    – JDługosz
    Apr 1, 2015 at 7:58
  • @JDługosz Read my comment again. I never mentioned backdoors. I intentionally tried to word it to avoid sounding like I was referencing backdoors, but I guess I failed at that.
    – Cole Tobin
    Apr 1, 2015 at 15:27
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I've used a flash drive with hardware-based encryption with success on Windows/Linux. I suspect it was a rebranded version of this. I formatted to FAT32, I don't see any reason it wouldn't work with Mac.

"Truecrypt" is also a good answer, though again, I've not used it on Mac.

For my encrypted backups on Linux, I use Duplicity. Duplicity requires you be PGP-savvy, but allows you to do incremental encrypted backups. There's also a Mac port. There's a GUI front end, but I haven't got experience with it.

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  • Wow, their prices are high: you'd think that the memory size would add only as much to the cost as normal USB flash memory drives, since you already paid for the encryption microcontroller. I can't find it now, but I saw a product in development that was a microSD-to-SD adaptor that did the encryption. A USB dongle that took replaceable SD cards would be a great way, if anyone makes such a thing.
    – JDługosz
    Apr 1, 2015 at 4:17
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Update:

Take the following into consideration before using EncFS:

Warning: A security review (February 2014) of encfs discovered a number of security issues in the stable release 1.7.4 (June 2014). Please consider the report and the references in it for updated information before using the release.

It may be prudent to wait for the anticipated EncFS2 stable release.

Original post:

You can do this with EncFS.

On OSX you'll want Mac fusion. This example follows setting one up on dropbox - but it works basically the same for any other use.

enter image description here

For linux:

$ encfs ~/.name ~/name

Note that EncFS comes with some caveats, quote:

... a number of advantages and disadvantages compared to these systems. Firstly, it does not require any root privileges to implement; any user can create a repository of encrypted files. Secondly, one does not need to create a single file and create a file-system within that; it works on existing file-system without modifications. This does create a few disadvantages, though; because the encrypted files are not stored in their own file, someone who obtains access to the system can still see the underlying directory structure, the number of files, their sizes and when they were modified. They cannot see the contents, however. This particular method of securing data is obviously not perfect, but there are situations in which it is useful.

This type of system works great for cloud storage sync'ing solutions - but may not fit the needs of your project. In any case, it is an option.

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