Mac file encryption software like Knox is hard to find   it encrypts files and then hides them, it scored the highest in our ease-of-use tests, and it's free. It has a few drawbacks, particularly the increase in encrypted file size, that keep it from being as strong as the top-rated Mac encryption software, but it's an excellent choice for free, basic encryption.

We tested Knox alongside all of the other Mac encryption software in our lineup. After installing Knox, we were able to quickly start encrypting files for tests. We started with 63 files that totaled 134.5MB. This program took about 30 seconds to create a vault in which we were able to drag and drop our files. This is the point where you enter a password for the vault, then you can just close the vault and the program and know your files are secure.

Decryption isn't anything you have to wait for   you simply open the program and the vaults you want, and then enter your passwords and you have access to your files. Although it took a while to create a vault, that's the only time you'll be waiting at your computer while the program works.

Knox uses sparse bundles, which are disk images that are supposed to use only as much space as the data that is in them. You can create these vaults at whatever size you need and then add more files later if you create a large one. However, we were surprised to see that the vault we created at 200MB that contained only 134.5MB inflated to 764MB. This can be a problem if you have limited disk space, especially if you're working with bigger files.

Like the best Mac encryption software, Knox uses Advanced Encryption Standard (AES) 256-bit key encryption to effectively scramble your data. This algorithm is what the U.S. government trusts to keep its classified information secure.

Knox, as is standard for Mac encryption software, uses the built-in features of Mac's operating system. Mac OS X includes a password assistant that can help you choose a strong password that's unlikely to be cracked by anyone and a password strength meter that can show you just how secure your password is.

AgileBits, the company that created Knox, has stopped updating this software, but it is still available. Mac users who run any of the operating systems from Lion (10.7) to El Capitan (10.11) can use this software. Although the software isn't likely to have any updates, let alone regular updates, AgileBits' support team still answers questions, and you can still find a lot of helpful documentation devoted to Knox on the company's website.

Between its use of Mac's password assistant and its ability to hide your encrypted files, Knox handles the most important functions of an encryption program. This is a good free solution for file encryption on your Mac   just make sure you have enough space on your hard drive to accommodate bloated vaults.

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