How to read legacy FileVault formats on your Mac
All good things must come to an end, we’re told, and macOS 10.13 was the very end of the original FileVault, Apple's file encryption format introduced in OS X Panther 10.3. With the original FileVault, a Mac encrypted a user’s home directory and mounted it as a disk image, more or less. When OS X Lion 10.7.4 appeared, it offered FileVault 2, full disk encryption (FDE), which protects your entire drive by using a special startup procedure at boot time that lets you log in to unlock it. It’s much better than the original directory method, but it required faster Macs to work efficiently enough.