Mac OS X comes with built-in encryption utility. You can use it to encrypt any file by creating a new virtual encrypted disk.
Here's a step-by-step guide:
1. Open "Disk Utility" (Applications > Utilities).
2. Click "New Image".
3. Enter the name of a disk, for example, "Encrypted disk", select disk size (for example 40 MB, if that’s enough for your files), select AES-128 (recommended) encryption, and click "Create".
4. You’ll be asked to enter password. Do it. (Deselect Remember password for more security.)
Now you can double-click this disk image to mount it and view and edit files inside it.
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If you're looking for an easier way to encrypt your journal, Mémoires application supports it out of the box.
