How do I securely delete my 2014 Air's SSD before selling it?

stfwayne · Nov 19, 2014

I was preparing to sell my Air on Craigslist/eBay and did a CMD+R to get to the Internet Recovery Screen then went into Disk Utilities and erased the drive and reinstalled the OS X (Yosemite)

I am running a 2014 Macbook Air, i7, 8gb of ram with a 128gb SSD

But after reading alot on here and on the internet about how SSD can not be securely wiped i am a bit worried that someone may be able to access my personal information / work files.

Ive read that you can Erase Free Space but how is that going to prevent someone from recovering the files that have already been deleted by the first deletion?

Ive also read that you should use FileVault2 encryption

Most Macs allow you to wipe the hard drive when you go into Disk Utilities -> Erase --> Security options but the security options button is grayed out on my Air and from what i understand any newer Air after 2011.

Can anyone help me dont want to physically destroy the drive and purchase a newer drive to install inside

motrek · Nov 19, 2014

stfwayne said:
I was preparing to sell my Air on Craigslist/eBay and did a CMD+R to get to the Internet Recovery Screen then went into Disk Utilities and erased the drive and reinstalled the OS X (Yosemite)

I am running a 2014 Macbook Air, i7, 8gb of ram with a 128gb SSD

But after reading alot on here and on the internet about how SSD can not be securely wiped i am a bit worried that someone may be able to access my personal information / work files.

Ive read that you can Erase Free Space but how is that going to prevent someone from recovering the files that have already been deleted by the first deletion?

Ive also read that you should use FileVault2 encryption

Most Macs allow you to wipe the hard drive when you go into Disk Utilities -> Erase --> Security options but the security options button is grayed out on my Air and from what i understand any newer Air after 2011.

Can anyone help me dont want to physically destroy the drive and purchase a newer drive to install inside

I have sold a bunch of computers and never worried about this in the past, although recently I guess I have been using FileVault which eliminates the possibility.

As soon as you start writing to the formatted disk, you're going to screw up what was on there before, i.e., make it unrecoverable. So you already started that process by reinstalling the OS.

I suppose if you wanted to finish the job you could copy inconsequential files onto the drive until it was basically full.

Maybe find a big file like a movie or something, copy that to the drive, and duplicate it until the drive is more or less full? That should do the trick.

Edit: I believe you shouldn't do a "secure erase" on an SSD... that is more for hard disks, where there are magnetic remnants of data on sectors even if you overwrite them. So secure erase will write random data to the same sectors over and over to try to eliminate these traces of old data. But if you try to do this to an SSD, the random data you write will be written to different parts of the chips each time so all you'll succeed in doing is wearing out your SSD faster.

stfwayne · Nov 21, 2014

motrek said:
I have sold a bunch of computers and never worried about this in the past, although recently I guess I have been using FileVault which eliminates the possibility.

As soon as you start writing to the formatted disk, you're going to screw up what was on there before, i.e., make it unrecoverable. So you already started that process by reinstalling the OS.

I suppose if you wanted to finish the job you could copy inconsequential files onto the drive until it was basically full.

Maybe find a big file like a movie or something, copy that to the drive, and duplicate it until the drive is more or less full? That should do the trick.

Edit: I believe you shouldn't do a "secure erase" on an SSD... that is more for hard disks, where there are magnetic remnants of data on sectors even if you overwrite them. So secure erase will write random data to the same sectors over and over to try to eliminate these traces of old data. But if you try to do this to an SSD, the random data you write will be written to different parts of the chips each time so all you'll succeed in doing is wearing out your SSD faster.

I did a 3 pass deletion and turned on FileVault encryption with a fresh install of Yosemite

Hopefully that should be enough!

Thanks for your response i appreciate it!

cruisin · Nov 22, 2014

SSDs always reserve a portion of their space for wear levelling so you will never erase the whole drive (unless you basically erase the drive a lot of times). Luckily, this is impossible to access unless you have access to really expensive machines and people who do this for a living.

The wipe and the encryption of the drive should take of erasing the drive. Your data is now "erased"

.

motrek · Nov 22, 2014

stfwayne said:
I did a 3 pass deletion and turned on FileVault encryption with a fresh install of Yosemite

Hopefully that should be enough!

Thanks for your response i appreciate it!

No problem but I think you might have missed the plot a little.

To be clear, FileVault encrypts YOUR files. So if you WERE using FileVault, your old files would have been encrypted and thus unrecoverable.

Turning on FileVault now doesn't really help you. It will encrypt the new owner's files and not have any effect on the recoverability of your old unencrypted files which are still on there.

Also, you should never do an n-pass deletion on an SSD. As I explained in my previous post, that's for overwriting data on hard drives. It works by writing different data to the same locations over and over. But with an SSD, the way they work internally, logical locations are mapped to constantly-varying physical locations. So there's no way to write different data over and over to the same physical location. All you succeed in doing is wearing out your SSD.

I assume this point is moot since you've presumably already sold the laptop but if anybody else is reading this thread, I would go with my method of just filling up the drive with inconsequential files and then deleting them.

cruisin · Nov 22, 2014

Turning on file vault and then erasing the partition should give the same benefits as overwriting the drive with random files, just be much quicker.

motrek · Nov 22, 2014

cruisin said:
Turning on file vault and then erasing the partition should give the same benefits as overwriting the drive with random files, just be much quicker.

Anything that's quick isn't actually going to erase the drive. Just mark it as empty. Whatever was on there could still be recoverable.

Not sure why people are so reluctant to fill up the drive with random files (or just one big file duplicated over and over). It's easy to do and shouldn't take THAT long and there's no reason to mess with FileVault.

cruisin · Nov 22, 2014

Whatever was on there could still be recoverable.

But the only thing that is recoverable is the old encrypted drive, and unless you have the key then you are looking at gibberish. So unless they have the key, this is much quicker than manually copying files until the drive fills up.

It is not as perfect as if the drive was encrypted from the start, but it is still pretty good.

motrek · Nov 22, 2014

cruisin said:
But the only thing that is recoverable is the old encrypted drive, and unless you have the key then you are looking at gibberish. So unless they have the key, this is much quicker than manually copying files until the drive fills up.

It is not as perfect as if the drive was encrypted from the start, but it is still pretty good.

The OP had already formatted the drive and reinstalled the OS, so turning on FileVault is not going to accomplish anything. It won't encrypt the files that were on the drive since those are now erased.

As for copying files until the drive fills up, I have no idea why you think this might be such a chore. A rip of a DVD is around 9 gigabytes. Copy that to the SSD. Takes a few minutes. Duplicate it a few times, takes a few more minutes. Then you're done.

cruisin · Nov 24, 2014

Most people do not have a image lying around. And how will they make one on an Air with no drive?

motrek · Nov 24, 2014

cruisin said:
Most people do not have a image lying around. And how will they make one on an Air with no drive?

Come on, use some creativity. It doesn't have to be a DVD rip.

Zip up your MP3 collection if you need a big file. Copy it from your current computer to an external drive, and from the external drive to the computer you want to sell.

MacGekko · Jul 20, 2015

motrek said:
Anything that's quick isn't actually going to erase the drive. Just mark it as empty. Whatever was on there could still be recoverable.

Not sure why people are so reluctant to fill up the drive with random files (or just one big file duplicated over and over). It's easy to do and shouldn't take THAT long and there's no reason to mess with FileVault.

Motrek, I have to return a Macbook Pro, I turned on FileVault, erased the HD and reinstalled Yosemite but I would like to try your advice, how can I accomplish this in a fast manner, the only problem is I don't have an external dvd drive so I can't burn a movie and duplicate such a file, what would be my options?

motrek · Jul 20, 2015

GordonGekko999 said:
Motrek, I have to return a Macbook Pro, I turned on FileVault, erased the HD and reinstalled Yosemite but I would like to try your advice, how can I accomplish this in a fast manner, the only problem is I don't have an external dvd drive so I can't burn a movie and duplicate such a file, what would be my options?

I saw your PM about this and I think you're on the right track with making a ZIP file of MP3s.

newellj · Jul 21, 2015

GordonGekko999 said:
Motrek, I have to return a Macbook Pro, I turned on FileVault, erased the HD and reinstalled Yosemite but I would like to try your advice, how can I accomplish this in a fast manner, the only problem is I don't have an external dvd drive so I can't burn a movie and duplicate such a file, what would be my options?

If the drive was encrypted when you erased it, no one short of the NSA is going to be able to get anything meaningful off the drive.

motrek · Jul 21, 2015

newellj said:
If the drive was encrypted when you erased it, no one short of the NSA is going to be able to get anything meaningful off the drive.

I read his post as: he was using the drive, THEN turned on FileVault... I am not sure that is very secure with an SSD. It wouldn't surprise me if files that were on the drive before turning on FileVault are still recoverable.

In any case, my idea of filling up the drive by duplicating a harmless file doesn't take long and should be secure.

MRrainer · Jul 21, 2015

Kroll has some info on this:
http://blog.krollontrack.co.uk/top-tips/securely-erase-ssds-4-questions-answered/
Also, there are various presentations floating around.
Basically, you should really use FileVault from the very beginning. Because if you do this, nothing unencrypted ever hits the disk.

motrek · Jul 21, 2015

MRrainer said:
Kroll has some info on this:
http://blog.krollontrack.co.uk/top-tips/securely-erase-ssds-4-questions-answered/
Also, there are various presentations floating around.
Basically, you should really use FileVault from the very beginning. Because if you do this, nothing unencrypted ever hits the disk.

Yes, good advice.

The reason I made my suggestion (duplicating a large file until the drive is full, instead of using secure erase) is because secure erase software is still designed for hard drives and is inappropriate for SSDs.

If you run a secure erase program on an SSD, it will cause a huge amount of wear to the SSD and not really accomplish anything... the logical blocks it rewrites are constantly reorganized by the SSD firmware, so there's no guarantee that anything valuable is ever overwritten.

If you fill up a drive by duplicating a big file, then the SSD is basically forced to overwrite most of the blocks, because it has to store all that data somewhere!

newellj · Jul 21, 2015

motrek said:
I read his post as: he was using the drive, THEN turned on FileVault... I am not sure that is very secure with an SSD. It wouldn't surprise me if files that were on the drive before turning on FileVault are still recoverable.

In any case, my idea of filling up the drive by duplicating a harmless file doesn't take long and should be secure.

I may have mis-read or mis-remembered his post - the order you describe probably achieves nothing, I agree.

newellj · Jul 21, 2015

MRrainer said:
Kroll has some info on this:
http://blog.krollontrack.co.uk/top-tips/securely-erase-ssds-4-questions-answered/
Also, there are various presentations floating around.
Basically, you should really use FileVault from the very beginning. Because if you do this, nothing unencrypted ever hits the disk.

Yes, and the performance impact of FV2 on newer Macs is minimal.

How do I securely delete my 2014 Air's SSD before selling it?

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