Security of Encrypted Disk Images

[CharPatton]

If one uses Apple’s Disk Utility to create an encrypted disk image, what happens when SuperDuper is running to the data when the (unencrypted) image is mounted on the desktop?

Does SuperDuper copy both the encrypted image and the unencrypted data to the backup device? Or does it only copy the secure encrypted data to the destination?

Nothing urgent on this, just curious. Thank you!

[dnanian]

If you're trying to copy the drive that hosts the image, the encrypted version is copied. Note, though, that backups should NOT be done when images hosted on those drives are open: the resulting backup will not necessarily have an accurate representation of the image when it's not closed/saved.

[CharPatton]

Interesting. This answers the question from a practical standpoint, but I'm intellectually curious to know what is going on with the encrypted source disk image versus the mounted (unencrypted) disk image.

Is it correct to state that the encrypted source disk image stays unchanged the whole time the data on the mounted (unencrypted) disk image is being read and written to? And that the encrypted source disk image is only changed when the mounted (unencrypted) disk image is ejected (unmounted)?

As always, thank you for educating those of us who are newbies!!!

[dnanian]

No. There's no way to know the state of the on-disk version of a disk image when it hasn't been written. It is NOT necessarily "flushed", so it could be partially updated on disk. Just no way to know. But it's certainly changed before you close it.

[CharPatton]

Interesting.

As always, thank you! Your efforts and the superb quality of SuperDuper are truly appreciated.

[astrodog]

Interesting. This answers the question from a practical standpoint, but I'm intellectually curious to know what is going on with the encrypted source disk image versus the mounted (unencrypted) disk image.

Is it correct to state that the encrypted source disk image stays unchanged the whole time the data on the mounted (unencrypted) disk image is being read and written to? And that the encrypted source disk image is only changed when the mounted (unencrypted) disk image is ejected (unmounted)?

As always, thank you for educating those of us who are newbies!!!

I thought the data in an encrypted disc image stays encrypted, and is only decrypted when it is copied out of the image. I've used some very large encrypted images, and to decrypt 20-30GB of data would take an age upon mounting if the entire image was then decrypted.

[dnanian]

The on disk version is always encrypted. But it's not always in a stable state.