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How do you encrypt a single folder on Mac OS X without using a Disk Image?

I have heard you can use a Disk Image to do this but I don't want a giant 8 GB (the size reccomended here) Disk Image just sitting there which I will probably never fill up.

Thanks in advance!

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2 Answers 2

up vote 4 down vote accepted

If you need compatibility with other operating systems, another option would be to use TrueCrypt. TrueCrypt can create an dynamic volume that functions very similarly to a sparse disk image created by Disk Utility.

Inconvenient, though, is that dynamic volumes must use the NTFS filesystem, so if you want to create one you'll need to (a) create the volume on a Windows computer, and (b) install MacFUSE and NTFS-3G on any Mac you want to access the volume.

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Use Disk Utility to create a new image, and for "Image Format" make sure you use "Sparse Bundle Disk Image", then select your encryption type.

"Sparse" means the image will start at a relatively small size and grow only as much as it needs to contain what you put in it.

By the way, there is another image format called "Sparse Disk Image" (not a bundle). This will function similarly; the difference is that a sparse bundle behaves intelligently when using Time Machine to back it up, but a sparse disk image does not. If you change one bit inside a sparse disk image, Time Machine will have to make a copy of the entire file, but if you use a sparse bundle it will only copy the small portion that changed. The only downside is that the sparse bundle was added in Leopard; use a sparse disk image if you need compatibility with Tiger or older.

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What is the difference between Sparse Bundle Disk Image and Sparse Disk Image? – Wuffers Apr 24 '10 at 18:07
When deleting large files from within such image, then see How to reclaim all/most free space from a sparsebundle on OS X – Arjan Apr 24 '10 at 18:07
Just added the difference, since I had to go learn it myself =) – Stephen Jennings Apr 24 '10 at 18:08
Thanks! – Wuffers Apr 24 '10 at 18:09
Is anyone aware if there are tools to read such an encrypted sparse bundle disk image in other linux environments? – drevicko Jun 27 at 0:54

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