Creating & using Blank Disk Images w/ encryption

[Aniej]

I am a bit unfamiliar with doing this and don't want to do something harmful so I thought I would ask the usual suspects for some advice in advance rather than post-hoc. I read the disk utility help blurb on this and feel ok, but would really appreciate some further help.

1. what would be an appropriate size to select, obviously this depends on the useage, but a ballpark for small average above average and large would be great.

2. what exactly is a disk image, i.e., is it just as the name suggests?

3. is there anything I should know about encryption if I am going to use it, aside from not forgetting the password?

4. where is an appropriate place to store the disk image if you are looking to keep it out of the way and confidential?

5. is there a way to make this disk image somewhat invisible?

6. the help blurb said I can add new files in the future and that they would be placed in a volume on my desktop and that I can drag files to it. what then happens with this volume or what am i supposed to do with it if i don't want it living on my desktop?

thanks i really appreciate the advice. and, happy new year in advance.

 

[Aniej]

Calling madjew, your assistance is needed.

 

[mad jew]

1. what would be an appropriate size to select, obviously this depends on the useage, but a ballpark for small average above average and large would be great.

Well, create a sparse disk image with a ceiling limit. This way, the image will only take up as much space as it needs, as opposed to a regular image which will take up its maximum space at all times. Umm... The ceiling size really depends on what you want put in this image.

2. what exactly is a disk image, i.e., is it just as the name suggests?

Think of it as a virtual partition. It can hold information in it that can be separated from the rest of your hard drive, despite it still actually being stored on the hard drive. It can be encrypted to ensure your data is available only to those you want.

3. is there anything I should know about encryption if I am going to use it, aside from not forgetting the password?

Not really. Don't let Keychain remember the password because then it defies the whole point.

4. where is an appropriate place to store the disk image if you are looking to keep it out of the way and confidential?

Assuming you're on 10.4, Spotlight will be able to find it in a flash unless you tell Spotlight not to index the area you keep it in. Spotlight will not show search results from within an encrypted disk image unless it is mounted though.

5. is there a way to make this disk image somewhat invisible?

I don't use it, but TinkerTool should be able to let you view hidden files. Then, all you have to do is create the disk image with a name beginning with a full stop (period) and it'll be hidden unless TinkerTool is set to let you see hidden files. A name such as .Diskimage.dmg should be hidden. I emphasise the should.

6. the help blurb said I can add new files in the future and that they would be placed in a volume on my desktop and that I can drag files to it. what then happens with this volume or what am i supposed to do with it if i don't want it living on my desktop?

I think you're talking about mounting and unmount it. If you double click on a DMG, it'll mount on the Desktop with a white disk image icon (unless you manually change this). This acts as a folder from which you can add, delete, move and rename files within your disk image (assuming you've entered the password). Unmounting this drive is as simple as ejecting a CD. To remount it, you need the password.

I hope that helps a little, mate.

 

[mkrishnan]

I don't use it, but TinkerTool should be able to let you view hidden files. Then, all you have to do is create the disk image with a name beginning with a full stop (period) and it'll be hidden unless TinkerTool is set to let you see hidden files. A name such as .Diskimage.dmg should be hidden. I emphasise the should.

If you have an encrypted disk image, why do you need to hide the fact that you have the image, in and of itself? The problem with any solution like this is that once you put in Tinkertool to see hidden files, hidden files are visible, so it defeats the purpose of giving it a dot name.

I guess, if you really want to, instead of using tinkertools, give it that dot name and then open it from terminal with a command like:

open ./.aniej.sparseimage

But the easier thing is to just give it a normal, inconspicuous name, encrypt it, and leave it in plain sight in your Docs directory.

 

[mad jew]

I completely agree. Of course, I was assuming TinkerTool would be used to toggle whether hidden files could be viewed. Nevertheless, I think it's a bit redundant and I wouldn't bother hiding it.

 

[Mernak]

But the easier thing is to just give it a normal, inconspicuous name, encrypt it, and leave it in plain sight in your Docs directory.

and maybe even change the icon and hide the .dmg part Best way to hide something is to keep it in plain sight.

 

[Aniej]

Well, create a sparse disk image with a ceiling limit. This way, the image will only take up as much space as it needs, as opposed to a regular image which will take up its maximum space at all times. Umm... The ceiling size really depends on what you want put in this image.

Your comments were awesome and really helpful. thanks. I am a bit confused on this part here though. conceptually i understand, but as a matter of implementing this I am unclear; are you using ceiling to refer to the option when making a disk image to place a limitation on the size of the disk image?

Also, what are the implications of making a disk image too large or too small? can an image that is too small be increased later and can an image that is too big be made smaller?

 

[Xenesis]

While I haven't used 10.4's Disk Image tool yet, it was reasonably easy to use Disk Utility in 10.3.9 to convert a disk image from one size to another.

Making it too large basically just means that it'll take up more room on your hard drive. Too small, it might not hold what you want it. But that's about all.

 

[Aniej]

so then if it is too small then it will reject the file that it too large, but i am able to remedy this by making it larger and then drop the file i want in it?

 

[mkrishnan]

There are two kinds of disk images:

A regular disk image: If the disk is going to be 600 MB, you make a 600 MB image file. The image file is this same size whether it has one file in it or is almost full.

A sparse disk image: If the disk is going to be 600 MB, you define the maximum possible size of the image contents to be 600 MB. The image file, however, doesn't reach a size of 600 MB itself until you actually put 600 MB of files in it.

An example of using a sparse disk image file in this way is that I made a 40GB image file on my iMac's hard drive to use to make a backup of my iBook's drive in it. I chose this size because my iBook's hard drive is 40 GB in capacity. So I know that, no matter how full the iBook gets, it will always fit in this disk image, right?

Right now, the image file is 26.3 GB because my iBook hard drive is not full, and that's all there was to put in it.

Does that make sense?

To answer your question, you should make the sparse disk image's ultimate capacity big enough so that you feel safe you will never need more than that. Typically you can make it many GB larger than you immediately need it. That way you don't have to worry about making it larger later, although I guess this can be done and isn't so complicated. It'll still probably be really slow, right? I've never done that.

 

[Aniej]

There are two kinds of disk images:

A regular disk image: If the disk is going to be 600 MB, you make a 600 MB image file. The image file is this same size whether it has one file in it or is almost full.

A sparse disk image: If the disk is going to be 600 MB, you define the maximum possible size of the image contents to be 600 MB. The image file, however, doesn't reach a size of 600 MB itself until you actually put 600 MB of files in it.

An example of using a sparse disk image file in this way is that I made a 40GB image file on my iMac's hard drive to use to make a backup of my iBook's drive in it. I chose this size because my iBook's hard drive is 40 GB in capacity. So I know that, no matter how full the iBook gets, it will always fit in this disk image, right?

Right now, the image file is 26.3 GB because my iBook hard drive is not full, and that's all there was to put in it.

Does that make sense?

To answer your question, you should make the sparse disk image's ultimate capacity big enough so that you feel safe you will never need more than that. Typically you can make it many GB larger than you immediately need it. That way you don't have to worry about making it larger later, although I guess this can be done and isn't so complicated. It'll still probably be really slow, right? I've never done that.

Awesome awesome awesome answer. thank you very much for working through that with me, it makes complete sense now. I would just ask for one clarification to double check that sparse disk image would be the same thing as a blank disk image? And I trust that I can always make additional disk images if I feel that the material is important to keep separated?

 

[mkrishnan]

Awesome awesome awesome answer. thank you very much for working through that with me, it makes complete sense now. I would just ask for one clarification to double check that sparse disk image would be the same thing as a blank disk image? And I trust that I can always make additional disk images if I feel that the material is important to keep separated?

Yep - those are both correct. Should work out well for what you want.

 

[Aniej]

thanks again and happy new year.

 

[Aniej]

Can I change a read/write image into a sparse image?

 

[Aniej]

I meant to include this with the last question: can I simply delete a read/write disk image if I no longer want it and instead have decided to use a sparse image? does simply deleting it restore the disk space allocation, i.e., 40mb that I had for the disk image or are they lost and how do I actually delete this thing safely?

 

[Aniej]

 

[mkrishnan]

From the "outside," yes, the disk image is just a file. If you don't need it, you throw it in the trashcan, like any other file, and when you empty the trash, it's gone and the free space is back.

 

[Aniej]

solved. done and done. thanks