leaving no trails

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zoranb

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What ill be asking here is a little oposite to what users usually need. I want to know how can i permanently delete the files i have on OSX without leaving any chance of someone to use a retreive data application to see the files i had copied/worked and deleted on my mac.
What is the most secure way, so one cannot retreive deleted files from my hd? I know formating the drive might be one way to permanently loose data but thats a very drastic action cause u have to kill every data on the mac and i dont want to kill apps etc.
Some time ago in Windows (win98), i remember that, when defrag was made it wasnt very easy to locate/retreive deleted files, whats the case in OSX? How can i leave no trails to the person that will use my computer after me?
Just to inform, i do not have a second partition on my hd, i only have one partition for all!
 
drag all of your files to the trash can and select secure empty trash from the finder pull down menu. It will take a long time but it will work well.
 
In Disk Utility, there's an "Erase Free Space" button. This will let you overwrite all the unused space on a volume using one of three security levels. I believe "7-pass erase" is the equivalent of "Secure Empty Trash".

This can take many hours, depending on how much free space you have on your disk.
 
After these actions what are the possibilities that data can be retreived?

Also let me ask this, is this a safe action? Say for eg. i have a jpg picture, if i open it in Pshop and paint it all one color and then save and replace it, is the first version retreivable by any means?
 
If you want to read about secure data deletion, check this out:
http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html
Conclusion:
Data overwritten once or twice may be recovered by subtracting what is expected to be read from a storage location from what is actually read. Data which is overwritten an arbitrarily large number of times can still be recovered provided that the new data isn't written to the same location as the original data (for magnetic media), or that the recovery attempt is carried out fairly soon after the new data was written (for RAM). For this reason it is effectively impossible to sanitise storage locations by simple overwriting them, no matter how many overwrite passes are made or what data patterns are written. However by using the relatively simple methods presented in this paper the task of an attacker can be made significantly more difficult, if not prohibitively expensive.
Click to expand...

http://docs.info.apple.com/article.html?artnum=303462
http://en.wikipedia.org/wiki/Data_remanence

Simply editing a file will not delete previous contents completely.
 
There is a lot of discussion these days about secure data erasure. I think what eric2006 is trying to get across is that there are methods out there to recover the data - there always will be. Whether you are using some fancy low-level drive software, or whether you are examining the electron flow patterns on the surface media - there will always be methods.

The amount of effort you want to employ in erasing the data can only be determined by yourself. What degree of recovery is an acceptable risk to you? You can only reduce the possibility of data recovery - you can't eliminate it.
 
Ok i get it, so in theory, there will always ways of recovering files bla bla bla.
So the first thing and most simple to do is make sure that i use the Secure Empty Trash command.
Ok, so whats the 2nd and 3rd thing i can do, to prevent my files from beeing recovered? Remember that i dont want to delete any of the OSX files and apps already installed!
 
There's methods of erasure that will do a better job, but they also destroy the hard drive - such as degaussing.

You could also use the Filevault feature - at risk of system failure.
 
My suggestion: boot from an external disk for your top secret tasks and store the disk in a secure location.
 
You could put your most sensitive files in an encrypted disk image, and use them from there.

It all depends on the level of security you need. If you're worried about your government siezing your computer, then you'll have to go to great lengths.

I think Stephen Hawking once said that if you were to throw an encylopedia into the sun, you could recreate it atom for atom based on the sun's output......if you had godlike knowledge of the sun's mechanics. Information can never be destroyed; it can only be obfuscated so as to make it practically impossible to recover. :)

(Edit: Actually, I don't think it's really Stephen Hawking's quote, but just a cliche of the field. Like monkies on typewriters, I guess. See Do Black Holes Destroy Information? if you're geeky enough to care.)
 
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