If mac is re-imaged, does a protected DMG erase?

[pouchboy]

Hi. I have some sensitive family biz files in a password-protected DMG file. These files are also backed up via other methods. Regardless, as I am always worried about losing my Macbook, I have a question. If it's ever stolen and some re-images the whole computer, will the password-protected DMG file be erased, or will it just remain? Many thanks.

 

[hobowankenobi]

Depends. If they format the drive (most likely to erase all traces), yes EVERYTHING would be gone.

OTOH, if they chose to not erase the drive, and say....just used Recovery mode to reinstall, no user data would be erased.

Third option: drive not erased, but existing user account deleted: then yes, most likely (depending on the location) the dmg and all other user data for that user account would be deleted.

If you are worried, you should consider encrypting the entire drive with file vault, and be sure to have a decent login password, and be sure that the machine locks after a short period of time and on sleep (when lid is closed). That way ALL your data is irretrievable if you simply close the lid.

 

[pouchboy]

Got it. If I just turn File Vault on and have a good password, does that create the encryption? Many thanks.

 

[hobowankenobi]

Got it. If I just turn File Vault on and have a good password, does that create the encryption? Many thanks.

Yep. The entire disk. When you log out, it is encrypted. When you log in, it is decrypted.

The only practical way to get your data is a thief would have to steal the machine while you are logged in, and not let it sleep or reboot or log out. Then they could do everything you could do....without a PW. Your encrypted DMG would still require a PW, as would any admin tools they tried while it is booted.

One of the best things about full disk encryption is that with an unencrypted drive, the drive could be removed from the machine (or the Mac to be booted to Target Disk Mode, at least for 10.13 and older) and it would be fairly simple to bypass permissions and other normal security hurtles. An encrypted drive is always encrypted, and removing it from the machine does not change or weaken that.

File Vault is fairly painless. Just don't ever lose your PW...cuz it locks out everyone without the PW, even you.

 

[pouchboy]

Yep. The entire disk. When you log out, it is encrypted. When you log in, it is decrypted.

The only practical way to get your data is a thief would have to steal the machine while you are logged in, and not let it sleep or reboot or log out. Then they could do everything you could do....without a PW. Your encrypted DMG would still require a PW, as would any admin tools they tried while it is booted.

One of the best things about full disk encryption is that with an unencrypted drive, the drive could be removed from the machine (or the Mac to be booted to Target Disk Mode, at least for 10.13 and older) and it would be fairly simple to bypass permissions and other normal security hurtles. An encrypted drive is always encrypted, and removing it from the machine does not change or weaken that.

File Vault is fairly painless. Just don't ever lose your PW...cuz it locks out everyone without the PW, even you.

[doublepost=1549232807][/doublepost]Thank you. I am surprised that encryption is so easy...just turn it on and have a password that is secure. No encryption key or other complexities. I appreciate the explanation.