When you need to distribute a package of encrypted data more securely than possible with ZIP Encryption, or want a smoother workflow for encrypting some data when you’re not using it, you might consider creating an Encrypted Sparse Disk Image:
- Open Disk Utility (/Applications/Utilities/Disk Utility),
- Select File→New→Blank Disk Image…,
- Choose a large enough Size to contain all your data (be aware that the larger you make the image, the slower it will be to mount and unmount; the image will only take up as much space on disk as its encrypted contents; you may increase the image size later),
- Choose sparse bundle disk image as the Image Format, and choose the level of encryption you require,
- Choose a password to encrypt the image. Make sure to uncheck the Remember password in my Keychain box if you want to be prompted each time you attempt to mount the disk, and
- Click OK. Disk Utility will create a sparse bundle to hold your files. Don’t forget to delete the original folder.
Annoyingly, there used to be an option to create an automatically resizing Encrypted Disk Image using an existing folder as a base, but that’s disappeared in Mavericks.