I was looking for a solution to keep my financial data (quickbooks, excel, important documents, etc…) encrypted on OS X so that if my laptop were stolen, lost, etc… I wouldn’t have to worry about it. I also like to backup my data to my colocated Linux server so in the event that that machine were compromised I wanted to be protected. As it turns out, Mac OS X has the perfect solution for this: read-write encrypted disk images. Here’s how you do it:
1. Applications -> Utilities -> Disk Utility
2. Click New Image and then enter a filename, select Encryption AES-128, read-write disk image, and pick a disk size large enough to hold your data. It’s too bad it can’t dynamically grow as needed but you can always create a new and larger image if you outgrow the current one.
3. Click Create and enter the password you want to secure your files with and uncheck Remember password (add to Keychain) and then click OK. If you add the password to the keychain and your laptop is stolen then your no better off.
Now you can click on the .dmg file it created, enter your password, and the volume will show up on your desktop. Add any files you’d like to it, modify them, do whatever, and then when you’re done eject the volume. Voila, you now have an encrypted virtual disk where you can store you sensitive data.