Disk Image .dmg Does Not Ask For Password When Encrypted

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Disk Image .dmg Does Not Ask For Password When Encrypted Files

I cannot create an encrypted disk image. I have searched through the discussion forums here but have not found an answer. After I select the name, location, image format, encryption and I hit save, I get an error that says 'Unable to create '[file name].dmg'. (Resource busy)'. I've tried different locations, image format and encryption, but I keep getting the same message. Any ideas what the problem is and how I can fix it? Thanks.
NB: I want to create the disk image so that I can encrypt a few files with sensitive information. I do not want to use filevault, as I understand that it has downsides (e.g., free space needed to turn on and off, and backup with TM).

MacBook Pro (2008), Mac OS X (10.5.5), My first Apple computer: Macintosh 512

Posted on Dec 10, 2008 10:00 PM

14th December 2016

I prefer .dmg instaed of zip for archiving project data, etc. .dmg is handy for refering files, modify contents without extract files to somewhere.

.dmg can usable as like USB drive. Disk Utility tool can create/update .dmg from folder with various options. Options are like encryption, readonly, compression, etc.

But if you have tens of folders to archive, it’s better to use command line tools.

Create encrypted .dmg file

hdiutil is command line version of Disk Utility app. This command can mount/unmount/create/update disk image files. Please see man hdiutil for more detail.

Disk image .dmg does not ask for password when encrypted emails

Below script is part of my workflow of archiving project files. I’m using encrypted .dmg for archive. The script require prepare password file under $HOME/.dmg-password. Please create and store password for .dmg without LF.

And update permission like chmod 600 $HOME/.dmg-password to prevent read from other users. This sequence using password and encryption. But it’s not strong enough, reason described below.

Password

Preset password for .dmg in Key Chain

It’s kind of pain in neck entering password for opening .dmg everytime. If you open .dmg from Finder.app, the password dialog refuse copy & paste operation.

There is option “remember password in my keychain”. Concept is similar to this.

The password for disk image is stored in keychain which identified by UUID of .dmg. The UUID is referable by command like below.

Now you can store password through security command.

Disk Image .dmg Does Not Ask For Password When Encrypted

Unfortunatelly, there are no option like -stdinpass. So the password must be passed through command line argument. This mean optential leak through ps command or shell history.

By the way, I’m using below script for preset password to disk images.

Disk Image .dmg Does Not Ask For Password When Encrypted File

When opening .dmg from Finder, operating system ask authorisation of using password by diskimages-helper.

Disk Image .dmg Does Not Ask For Password When Encrypted Mean

You can skip this dialog by -A option of security command, but this option authorise for all applications. It’s better not use this -A option for better security.