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antdude
A Ninja Ant
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Securedly erase memory cards?

Will DBan work on these (e.g., very old SD mini and micro types from 16 MB to 2 GB sizes) or do I need to use another software for them?

Thank you in advance.



Kilroy
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Saint Paul, MN

If you're concerned destroy them.

Due to the way that they write there isn't a good way to wipe them.



antdude
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said by Kilroy:

If you're concerned destroy them.

Due to the way that they write there isn't a good way to wipe them.

Really? Don't they use the same method as Flash memory?


StuartMW
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1 edit

1 recommendation

said by antdude:

Don't they use the same method as Flash memory?

They are flash memory. All USB/SD/etc cards use flash memory. Not sure why Kilroy See Profile thinks they can't be wiped.

If you only have SD (vs CompactFlash, USB sticks etc) cards you can use the official SD Card Formatter with the overwrite option.

»www.sdcard.org/downloads/formatter_3/
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Don't feed trolls--it only makes them grow!


Blackbird
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reply to antdude

It may be that the program methodology for securely erasing them causes so many write operations that it "wears out" the limited number of lifetime writes for flash technology... in which case, there would be no "good" way to just "wipe" them. I'll leave it for an expert to pronounce authoritatively on this - but it is something that I've seen asserted elsewhere in months gone by...
--
“The American Republic will endure until the day Congress discovers that it can bribe the public with the public's money.” A. de Tocqueville



StuartMW
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Flash memory usually has bulk (entire chip) and sector/page erase functionality. Depending on whether they use NAND or NOR cells they're programmable on a block or individual word basis. Cells have to be erased before being (re)programmed so there's constant erase/program cycles no matter what data you write.

PS: I've written a bunch of code over the years to do all this. Some chips/devices are easier to manage than others.
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Don't feed trolls--it only makes them grow!



Kilroy
Premium,MVM
join:2002-11-21
Saint Paul, MN

1 recommendation

reply to StuartMW

If the card supports wear leveling you can't be sure that it is wiped.
--
“Progress isn't made by early risers. It's made by lazy men trying to find easier ways to do something.” ¯ Robert A. Heinlein



StuartMW
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Well the SD Card Formatter actually performs a bulk erase before formatting assuming the card supports it and you ask it to.

quote:
FULL (Erase):
This option initializes the file system parameter in the card, and initializes all the user data areas (Initialize it by executing erase processing (data deletion) of the card to all the user data areas). This option has the possibility that it takes the format time long according to the capacity of card. There is something that doesn't support to the erase processing according to the SD interface
device. The erase processing is skipped when "FULL (erase)" format type is selected in the unsupported environment. In this case it is same as selected QUICK option.

Some USB sticks can also be bulk erased/formatted with a utility provided by the manufacturer. I've used such in the past. That said you usually have to know the OEM to find the tool (if it exists).

That said you're correct that simply writing zeroes to the device using something like DBAN may not erase everything.
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StuartMW
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1 edit

1 recommendation

reply to antdude

. o O (more ant porn to get rid of? )

Back in the good ole days I'd run a powerful magnet over my floppies and then reformat them



antdude
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said by StuartMW:

. o O (more ant porn to get rid of? )

Yep. [grin]

So, where can we get this formatter you mentioned?


StuartMW
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1 recommendation

said by antdude:

So, where can we get this formatter you mentioned?

Um, click on the URL I posted?
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antdude
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said by StuartMW:

said by antdude:

So, where can we get this formatter you mentioned?

Um, click on the URL I posted?

Whoops, my bad. I missed that reply (so many replies already!!). Thanks.
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Ant @ AQFL.net and AntFarm.ma.cx. Please do not IM/e-mail me for technical support. Use this forum or better, »community.norton.com ! Disclaimer: The views expressed in this posting are mine, and do not necessarily reflect the views of my employer.


antdude
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1 edit
reply to StuartMW

said by StuartMW:

said by antdude:

Don't they use the same method as Flash memory?

They are flash memory. All USB/SD/etc cards use flash memory. Not sure why Kilroy See Profile thinks they can't be wiped.

If you only have SD (vs CompactFlash, USB sticks etc) cards you can use the official SD Card Formatter with the overwrite option.

»www.sdcard.org/downloads/formatter_3/

I will try it out later. No Linux port, eh? I hope full erase and full overwrites are enough.
--
Ant @ AQFL.net and AntFarm.ma.cx. Please do not IM/e-mail me for technical support. Use this forum or better, »community.norton.com ! Disclaimer: The views expressed in this posting are mine, and do not necessarily reflect the views of my employer.


StuartMW
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1 recommendation

said by antdude:

No Linux port, eh?

Geez, you're a fussy ant
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antdude
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said by StuartMW:

said by antdude:

No Linux port, eh?

Geez, you're a fussy ant

Ya, but it looks like I am limited to Windows and Mac ports so I will have to use that one then.
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Ant @ AQFL.net and AntFarm.ma.cx. Please do not IM/e-mail me for technical support. Use this forum or better, »community.norton.com ! Disclaimer: The views expressed in this posting are mine, and do not necessarily reflect the views of my employer.


Sr Tech
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join:2003-01-19
Valhalla, NY

2 recommendations

One way to check would be install Recuva and see if you can recover the data after wiping, if not you should be ok. Also Recuva can tell you the state of the file well as can perform overwriting as well.



antdude
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reply to antdude

dd

»sourceforge.net/projects/dban/fo···/4739935

I got a Dban forum reply since others and I asked about this:

"This feature is not supported. You can use
sudo dd if=/dev/zero of=/dev/sdX
or
sudo dd if=/dev/urandom of=/dev/sdX,
where /dev/sdX is your memory card."

Is dd's method secured?
--
Ant @ AQFL.net and AntFarm.ma.cx. Please do not IM/e-mail me for technical support. Use this forum or better, »community.norton.com ! Disclaimer: The views expressed in this posting are mine, and do not necessarily reflect the views of my employer.



angussf
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Tucson, AZ
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said by antdude:

»sourceforge.net/projects/dban/fo···/4739935

I got a Dban forum reply since others and I asked about this:

"This feature is not supported. You can use
sudo dd if=/dev/zero of=/dev/sdX
or
sudo dd if=/dev/urandom of=/dev/sdX,
where /dev/sdX is your memory card."

Is dd's method secured?

Not sure what you mean by "secured" in this context.

The first dd command fills the sdX with zeros, the second with random data. Since it completely fills the disk, wear-leveling shouldn't prevent it from working as the entire disk is written to. Fillings with zeros is faster and the reasoning behind filling spinning disks with random data* doesn't apply to SD cards or flash drives.

See
dd (Unix) - Wikipedia, the free encyclopedia
»en.wikipedia.org/wiki/Dd_(Unix)#Disk_wipe
and
Dd - Destroyer of Disks - Noah.org
»www.noah.org/wiki/Dd_-_Destroyer_of_Disks
* Wiping a Hard Drive with DD - MarkSanborn.net
»www.marksanborn.net/howto/wiping···-with-dd
Due to the way hard drives are made it is often possible to determine what was written beneath the most current write operation. If you write the entire drive with zeros, it will be quite easy to see what data was written before. It will be the one that is not a zero!
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Woody79_00
I run Linux am I still a PC?
Premium
join:2004-07-08
united state
reply to antdude

Re: Securedly erase memory cards?

if i was you, i would just take these cards out in the garage and smash them with a hammer and then light the pieces on fire with some lighter fluid.

if your concerned about data being recovered off of them, then just destroy them and sleep well.



StuartMW
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reply to angussf

Re: dd

said by angussf:

(BTW this quote is from Mr Sanborn's article and not angussf See Profile)

quote:
Due to the way hard drives are made it is often possible to determine what was written beneath the most current write operation. If you write the entire drive with zeros, it will be quite easy to see what data was written before. It will be the one that is not a zero!

First off I have no idea what he means by that. If you write a zero you read back a zero. How you read back the "data written before" is a mystery to me.

Also it is my understanding that the DoD standard requires writing zeroes three times not just once. Pretty sure that if that is done you won't be able to read the "data written before" .

But as noted this applies to HD's and not memory cards. Totally different technologies. Different techniques are needed.
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angussf
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Tucson, AZ
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said by StuartMW:

First off I have no idea what he means by that. If you write a zero you read back a zero. How you read back the "data written before" is a mystery to me.

Also it is my understanding that the DoD standard requires writing zeroes three times not just once. Pretty sure that if that is done you won't be able to read the "data written before" .

But as noted this applies to HD's and not memory cards. Totally different technologies. Different techniques are needed.

Hard disks often have some remaining trace of the former data, called Remanent (or Remnant) Magnetization. Writing zeros once can leaves traces of it since the HDD is a physical device and head-to-track alignment isn't perfect as the drive ages. Writing zeros 3 times would erase it more securely, and writing random data would make it much harder to figure out what the RM traces are.

Flash drives store data in a different way, and I don't think that there is any remaining trace of the data after overwriting with zeros. But if you're truly paranoid use the "urandom" version of 'dd' and do it three times.

More info here:
When you delete a file or folder, the area around the place where your data was stored still has some memory called Remanent Magnetization.

The remanent magnetization is the permanent magnetization that remains after the magnetization of the original track is changed to zero (data wiped).

Analyzing the Remanent Magnetization helps some data recovery software programs to recover the wiped data.
Clearing Remanent Magnetization - Secure Disk Wipe
»www.isprotector.com/remanent-mag···ion.html
--
Angus S-F
GeoApps, Tucson, Arizona, USA
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StuartMW
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said by angussf:

Hard disks often have some remaining trace of the former data, called Remanent (or Remnant) Magnetization.

I'm aware of that. However reading that requires specialized and expensive equipment. Sure the FBI/CIA/etc can do that as can some data recovery companies. However an ordinary user, in possession of a stolen/discarded drive, is going to read back what was written to it.

The DoD method, of writing 0's 3 times, makes it impossible to read back the original information.

Flash drives store data in a different way, and I don't think that there is any remaining trace of the data after overwriting with zeros.

Flash memory uses charge not a magnetic field to store 1's and 0's. You can Google the physics if you're interested. The erased state of a flash cell is a '1' and they can only be programmed to '0'. To go from '0' to '1' a cell must be erased (vs programmed). Flash memory is also paged based (vs EEPROM) so to change one bit, in a page, from '0' to '1' you have to read the entire page into RAM, erase the page, and program the changed data in RAM back. As I said above I've written code, for many devices, to do all that. Now cards and USB sticks have a built-in controller to do that. However the method is the same.

Now in theory writing 1's (vs 0's for a HD) to a card/stick is just as good at erasing data. However any pattern is going to involve a erase/program cycle at the flash cell level and once the original cell charge is gone it's gone. There is nothing residual to read back.
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nonymous
Premium
join:2003-09-08
Glendale, AZ

Plus I thought todays large higher density disks made reading what was previously written all the much harder and more expensive.
That the ability to read previously written data was based on older lower density disks.



StuartMW
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said by nonymous:

Plus I thought todays large higher density disks made reading what was previously written all the much harder and more expensive.

That maybe true. I've always physically destroyed HD's that were faulty and couldn't be written with 0's. Gives one a perverse sense of satisfaction bashing them to bits with a hammer
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Don't feed trolls--it only makes them grow!


vaxvms
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reply to antdude

Re: Securedly erase memory cards?

16MB? I'd use a hammer or scissors.



antdude
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said by vaxvms:

16MB? I'd use a hammer or scissors.

I wonder if one could set up a RAID with it. Hehe!


antdude
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reply to StuartMW

said by StuartMW:

said by antdude:

Don't they use the same method as Flash memory?

They are flash memory. All USB/SD/etc cards use flash memory. Not sure why Kilroy See Profile thinks they can't be wiped.

If you only have SD (vs CompactFlash, USB sticks etc) cards you can use the official SD Card Formatter with the overwrite option.

»www.sdcard.org/downloads/formatter_3/

I finally tried it. Full Erase failed: »i.imgur.com/NWEnF.gif but Full Overwrite worked. Recuva couldn't recover any files so I hope that' secured enough.
--
Ant @ AQFL.net and AntFarm.ma.cx. Please do not IM/e-mail me for technical support. Use this forum or better, »community.norton.com ! Disclaimer: The views expressed in this posting are mine, and do not necessarily reflect the views of my employer.


Blackbird
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said by antdude:

... I finally tried it. Full Erase failed: »i.imgur.com/NWEnF.gif but Full Overwrite worked. Recuva couldn't recover any files so I hope that' secured enough.

A full overwrite should work for normal purposes. The problem that Kilroy See Profile was referring to is that in a flash device with wear leveling, there is a built-in mechanism that assures that all cells in the device get written-to roughly the same number of times, to prevent wear-out from literally writing/erasing/writing too often to the same cells. In such a case, any kind of partial rewrite to the device may skip over a previously-used (but marked as "erased") cell in favor of a cell that's been written-to fewer times. A forensic access of such a device can conceivably look into those previously-used cells and read what voltage states are still actually left in them. By fully writing to the device, all cells are over-written with the voltage states corresponding to the new signals.

That still leaves the question of whether an extremely sensitive, scientific lab analysis might still be able to see a slight variance from nominal in a cell's present voltage state, left from the data that was there prior to a single re-write... but the likelihood for success of that kind of forensics is very questionable, even among experts - unless the over-write signal is all ones or all zeroes. In that case, the faint 'echo' of the cell's stored voltage state that was there before may conceivably be slightly easier to detect and "read".
--
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vaxvms
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reply to antdude

said by Blackbird:

in a flash device with wear leveling, there is a built-in mechanism that assures that all cells in the device get written-to roughly the same number of times, to prevent wear-out from literally writing/erasing/writing too often to the same cells.

I'm curious. What's the typical expected life span for a flash device?
I read an article a while back (1 or 2 years ago) that indicated at least 100,000 Program/Erase Cycles. Higher quality devices 1,000,000 Program/Erase Cycles.


HA Nut
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USA
reply to antdude

I use USB Flash Tools »www.sdean12.org/USBFlashTools.htm

I make no guarantees about it but it works for me...