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full-disclosure-uk: Re: [Full-disclosure] Disk wiping -- An alte

Re: [Full-disclosure] Disk wiping -- An alternate approach?

From: E. Prom <e3prom_at_nospam>
Date: Tue Jan 26 2010 - 16:28:01 GMT
To: full-disclosure <full-disclosure@lists.grok.org.uk>


2010/1/26 Michael Holstein <michael.holstein@csuohio.edu>:
>> By the way, does somebody knows about the flash memory?
>> Is zeroing a whole usb key enough to make the data unrecoverable?
>>
>
> No, wear-leveling (done at the memory controller level) will dynamically
> re-map addresses on the actual flash chip to ensure a relatively
> consistent number of write cycles across the entire drive.

Agreed, if I want to delete one file : the file will be unlinked and the zeroes will be written somewhere else. But what if I zero the whole memory, with something like dd if=/dev/zero of=/dev/disk/by-id/my_flash_device? Whatever the order and places the zeroes are written, in the end there should be zeroes everywhere. Unless there is more blocks on the chip than it reports having, or some compression is used where instead of "00...0" it would write "0 from adress 1 to last address". I'm just speculating...

> The only way to completely "wipe" a flash disk is with a hammer.

That's the only reliable way, but a convenient way to erase data before lending a usb key would be nice.



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