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I have created a .sparseimage file of my Home folder on my 2009 iMac running OS 10.11.2 and have chosen a 17 character password which https://www.grc.com/haystack.htm notes that against an Offline Fast Attack Scenario (Assuming one hundred billion guesses per second) it would take 11.52 million trillion centuries to break.

My intention was to move it to my iCloud account but I find I cannot do so because it exceeds the limitation on file sizes that one is allowed to upload to one's iCloud account.

My question is, am I risking the possible compromise of this file by storing in on my Dropbox account? It has financial and other legal info that I would never want compromised.

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  • Why would you trust iCloud more than Dropbox? Where do you store your password and how secure is this storage? How do you intend to react if somebody points a gun at you and demands access to this data you "never" want to have compromised?
    – nohillside ♦
    Commented Jan 11, 2016 at 11:48
  • Wonderful! You answer a question by posing three questions that have no bearing on the original question asked. Not what I would call terribly helprul.
    – Penny11
    Commented Jan 12, 2016 at 2:59
  • Data security is a wide topic with a lot of factors to consider. I got the impression that you focus primarily on a medium strong password without considering other relevant aspects. For instance, if "never compromised" is a very strong requirement (because your business handles sensitive data), any (eve encrypted) cloud storage is probably too risky
    – nohillside ♦
    Commented Jan 12, 2016 at 5:32

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Your password will not be compromised by a brute-force attack. More likely it will fall to some other attack such as a password grabber or malware. Your computer will be able to open the sparseimage and therefore the obvious target to attack is your computer. The sparseimage and its password is safe enough, but you should ask yourself a few questions about why you want to approach securing your data this way.

  • Consider securing your high-value data in a small encrypted sparsebundle image within your Home folder, rather than unsecured within your Home folder and then trying to password protect it when you copy the whole Home folder into Dropbox
  • Storing your home folder in Dropbox sounds to me like a poor design (I am not a security expert). If you are looking for backup plans then Time Machine disks can be password protected too (this results in a sparsebundle protected by a strong password. Your Time Machine disk image, and the multiple machine snapshots which it contains, can then be stored in an off-site store of your choice. The Time Machine disk image can only be accessed with your strong password
  • Take care when trusting to estimates of password strength. A 17 character password can appear to be strong to an algorithm designed only to look for length and variety, but may well appear in the many non-dictionary password tables. For example "passwordpassword!" Contains 17 characters, but you can be sure that someone somewhere has already used it and it probably appears in a huge password table somewhere.
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  • My intention in storing the home folder off site was to be protected in the event of fire or of a break-in that might result in the loss of my two computers. The other, less elegant but probably more secure way I had considered was to buy two hard drives, copy my home folder to one, and store it in my nearby safety deposit box then, two weeks later, copy the current home folder to the other HD, return to the safety deposit box and swap the drive with the old Home folder with the drive with the new Home folder, and so on, ad infinitum.
    – Penny11
    Commented Jan 12, 2016 at 3:05
  • Penny - OK, and that's why I'm suggesting (see my bullet point 2) that the simple solution, and most useful in the event of disaster/theft is to make a Time Machine target with the default Time Machine setup. This can be a USB disk or an archive taken from a Time Capsule. Password-protect that disk with its Time Machine target (which includes multiple snapshots and can be from both machines). Now you can store that disk wherever you like, including a safe deposit box. You can even use two disks and alternate between them. (OSX can automatically use two separate disks).
    – Mic Channel
    Commented Jan 14, 2016 at 13:39
  • Thanks very much for that suggestion. Did you mean to say USB drive and not USB disk?
    – Penny11
    Commented Jan 14, 2016 at 17:53
  • Any large external disk will do. This can be USB drive or USB disk and these are cheaper and you don't need anything faster than USB. It can also be a FireWire or Thunderbolt disk. But, by default, the external disk should have capacity at least 1.5x -2x the size of the data you want to back up. Take both machines into account. This is likely to be 100GB to 1000GB depending on how much stuff you have already stored.
    – Mic Channel
    Commented Jan 16, 2016 at 18:25
  • I alternate between two 1000GB USB 2 disks, they are not fast but after the first backup I don't need speed. You can also set up Time Machine with small-capacity thumb drives (e.g. 32GB) but only by excluding lots of data, e.g. the applications folder, and only if you don't have a large quantity of documents, movies, etc. This works but defeats the purpose of a Time Machine being easy to use and easy to restore files from, because you would have to reinstall those Applications yourself.
    – Mic Channel
    Commented Jan 16, 2016 at 18:27

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