Mac OS Mojave. When I encrypt the whole external HDD, I click Erase > Format + Scheme, I can only see these options

Screenshot of Disk Utility's formatting options

But I don't see such options as if I was encrypting only some files on an external HDD. File > New image>

Screenshot of Disk Utility's Format and Encryption settings

So how to encrypt the whole external HDD with AES 256? Or maybe "Mac OS Journaled, Encrypted" is already in 256 AES?

  • I don't think macOS supports AES-256 for volume-level encryption (it does for disk images, but that's encrypted at the device level, not at the volume level). HFS+ encryption uses AES-128-XTS, and while I don't have any good documentation on it I think APFS encryption uses the same. However, the difference in security between AES-128 and AES-256 is negligible -- AES-128 might possibly become theoretically attackable if we ever develop large-scale quantum computers and someone wants to devote one to attacking you for a few years, but that's a pretty remote worry. Really, 128 bits is enough. Commented Aug 25, 2022 at 18:55

1 Answer 1


Apple uses AES 256 by default, but hardware secure enclaves too.
See Apple KB - Encryption and Data Protection overview and Apple Insider - Apple and Encryption

By default on Mac 'devices' are not encrypted, 'volumes' are. File > New Image creates a volume, stored as a .dmg [disk image] file or similar [sparsebundle, spareseimage etc].

  • I meant external HDD or FlashDrive USB.How do i encrypt them with AES 256? Commented Aug 25, 2022 at 11:25
  • You mean after the fact, rather than at erase/partition - that wasn't clear from your question - your images are of Erase & disk image creation, both of which are 'formatting' options. If already formatted, then Right click the volume in Finder > Encrypt. [Only works for GUID disks, not MBR] will convert HFS to APFS.
    – Tetsujin
    Commented Aug 25, 2022 at 14:55
  • No,it wasn't formatted Commented Aug 26, 2022 at 16:23
  • So… I'm not seeing what you're trying to do any more… At format, you've got the option of HFS or APFS Encrypted, as you already showed in your question. What's wrong with those?
    – Tetsujin
    Commented Aug 26, 2022 at 16:28

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