

How To Prepare a Mac For Sale - danbenjamin
http://danbenjamin.com/articles/2008/11/how-to-prepare-a-mac-for-sale

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KevinBongart
There's still a problem about the "factory fresh" feeling : when you turn a
brand new Mac on for the first time, you also have iLife already installed. I
always specify to people I sell my Mac to that iLife is ready. Here's how to
complete the "factory fresh effect" :

\- When you have just shut the computer down after the introduction video,
reboot it in Target Mode pressing cmd-T (hey, you're not already selling a
unibody MacBook, so there still is a Firewire port!). \- Connect another
Macintosh with a Firewire cable. The old one is mounted just like an external
hard drive. An expensive 2GHz Core 2 Duo external hard drive. \- Use that
Macintosh to drag'n'drop iLife suite into the old MacBook's Applications
folder. \- "Et voilà !"

~~~
kylec
The install disks that came with my MacBook (bought last August) had the
ability to install iLife with the rest of the operating system, so before you
get tricky with FireWire, you should check to see if the program is on the
install DVDs.

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lallysingh
They mention zeroing out the disk to prevent the next owner from recovering
your data.. actually using a 7 pass method.

How does this apply to SSDs? While I suppose a global use increment by 7 isn't
terrible, it does make me cringe a little.

~~~
pmjordan
While SSDs do wear out, it's very rare to actually end up with enough bad
blocks to run out of spare space. The write limit comes up whenever you
mention SSDs, but on a desktop or laptop computer it seems to be pretty much
irrelevant.

I do have to wonder why people still recommend 7-pass zeroing of _hard disks_
when _The Great Zero Challenge_ <http://news.ycombinator.com/item?id=117588>
still stands, and there is no evidence that it's possible to recover from a
simple dd if=/dev/zero.

With SSDs, there is the issue of certain blocks remaining untouched after
zeroing due to the wear leveling logic, although I doubt you'd need 7 passes
to flush it out - 1 pass with random bits and 1 pass with zeroes ought to
suffice. (the assumption being that this will touch even the masked blocks,
whereas two passes of zeroes will be detected, and already-zero blocks won't
be blanked, whereas a zero pass following a random pass will start by zeroing
unmapped blocks; if anyone knows the wear leveling algorithms better than me,
feel free to confirm/refute)

~~~
iigs
Gah. I had initially replied to the parent post with the Great Zero Challenge
link, submitted and saw that you beat me. :)

AFAIK, the technique for magnetic disk recovery after one dd pass is to remove
the heads and attempt to retrieve the data using laboratory equipment (more
sensitive than the original heads and _vastly_ more time consuming than the
commercial data recovery procedures).

You can't do that with SSDs, maybe you could attack the flash controller and
exploit something like a timing attack, or maybe you could try your luck
against the load leveling algorithms and dump the data from the flash chips
themselves, although this would involve at least desoldering the flash chips
in a big device or doing something nastier in an integrated package like a CF
card. If you lose there, the next stop would seem to be something involving an
electron microscope and trying to identify cells that used to be a zero and
are a one now, and vice-versa -- judging from:
[http://hackaday.com/2008/01/01/24c3-mifare-crypto1-rfid-
comp...](http://hackaday.com/2008/01/01/24c3-mifare-crypto1-rfid-completely-
broken/) it seems like state of the art currently is individual gate analysis,
I think this would have to go farther.

From a commercial perspective, it seems like there still is some drive to
build better tools:
[http://www.theinquirer.net/gb/inquirer/news/2008/10/28/flash...](http://www.theinquirer.net/gb/inquirer/news/2008/10/28/flash-
recovery-technology)

tl;dr: I agree, unless you are doing something criminal, I would use a single
dd if=/dev/zero of=/dev/diskdevice and get on with life.

~~~
pmjordan
Magnetic discs:

I agree with you that it ought to be possible in principle, although I find it
unlikely that data recovery companies would pass up revenue when they're quite
able to do it. The only explanation to me would be that they're being paid off
by somebody, e.g. governments, but again... WHY? My theory is that it _used_
to be possible, back when the data density was _much_ lower, larger chunks of
material were involved.

SSDs:

I would have thought that decoupling the flash chips from the controller logic
is the easiest way to get at any hidden data. You'll have to piece the data
together unless you can reverse-engineer the load-balancing algorithm,
although there won't be much left after one pass of zeroing anyway. I have my
doubts that you can get at residual charge from previous bit values in a
useful way.

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ilamont
It would have been helpful if the author had talked about how to find a buyer
-- is there a Mac-oriented site with classifieds, or is it best to try one's
luck with Craigslist?

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crabapple
reinstall the os?

