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I'd like to password protect a text file. Not necessarily a .txt file - just a file that's got text in it that I can edit with a standard text editor. I'd like to set a password and be prompted for it every time I open the file in any app. What's the best way?

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up vote 9 down vote accepted

You can put the file into an encrypted disk image.

  1. Open "/Applications/Utilities/Disk Utility"
  2. File > New > New Blank Image...
  3. In the new image dialog make sure to choose:

    • Encryption = 128 or 256-bit AES
    • Image Format = read/write disk image
  4. Because you chose encryption, you will be prompted to set a password for the disk image

You now have a password-protected disk image that you can save any kind of file in.

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Brilliant and simple. Thank you! – hairboat Dec 31 '11 at 20:09

Assuming you're the file's owner, a built-in and system-wide way to do this would be to adjust the file's permissions so that only a specific user or users (I'm assuming you want to lock the file so only you can view/edit it) can read or write to the file.

As Mark pointed out in the comments, however, this only protects you if:

  • No other user has admin rights to the machine, and
  • No one gains access to the machine while you're logged in

Making Coconut Man's solution by far a better one. I'll leave this answer here as an alternative that may be helpful in similar situations.

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Even then anyone with admin rights or physical access to the machine can read the file (+ you need to be aware of how backups store the data) – Mark Dec 31 '11 at 14:24
Good point! I'll edit my answer to describe it as an alternative with said limitations. – Dan J Dec 31 '11 at 23:03

You can print->save as PDF->password protect the PDF. It's not as transparent as having the .txt in a DMG, but it's easy enough to copy/paste the contents when it's time to edit.

Another container version akin to a DMG is OpenPGP. The suite for OS X is pretty nice, and it adds encrypt/decrypt to the services menu. It's very easy to right click your text file, choose 'Encrypt File' enter a password, verify, done.

Don't forget Keychain Access as well. It has the ability to create Secure Notes, which are password protected by the keychain they are stored in.

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These seem like great options. Will test them out! – hairboat Sep 27 '13 at 3:30

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