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Posts: 2 | Thanked: 0 times | Joined on Feb 2010
#1
Does anyone know of a way to securely delete files from an SD card on Maemo?? I've sold my n810 and need to get rid of passwords. Thanks for any help.
 
Posts: 2 | Thanked: 0 times | Joined on Feb 2010
#2
I should point out that it's set up as dual boot and the main system is on the SD card. I could just replace the card but I'd rather not have to rebuild everything.
 
Posts: 543 | Thanked: 181 times | Joined on Aug 2009 @ Universe,LocalCluster.MilkyWay.Sol.Earth.Europe.Slovenia.Ljubljana
#3
It's hard to secure wipe an SD card iirc. Or any other Flash storage for that matter. This is due to wear leveling. I could be wrong but that's the overall idea I got from reading various sites and articles.
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#4
Copy several times big Files with only "00" Bytes on your device until the device is full. It would help in the most cases to secure delete enought for ever.
 
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#5
I have this exact same problem with my N900 (getting a replacement from Nokia because of a dead pixel). What i did was to just create big files that fill upp all remaining space on the devices, after I removed the passwords by normal means (rm):

Code:
dd if=/dev/urandom of=bigfile
If thats to slow, like when filling up the 26GB partition i did
Code:
dd if=/dev/zero of=bigfile
to fill it with zeros instead or pseudo-random data.

dd will give an error when the device is full. In my case I had to run it several times on my 26GB partition considering its formated with FAT32 which only supporst 4GB files.

However there might still be a problem with this, atleast with normal SSDs, I dont know how the flash in the phones are constructed.
In SSDs there is extra space to replace weared out cells on the device, which I think is inaccessible by normal means. If a cell is weared out it might also be so that you can read from it but not write, which means your password would permanently be left on there.

Though this is only theoretical, I might even be wrong :P
I have no practical tests to back up my claims.
 

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#6
Originally Posted by Helmuth View Post
Copy several times big Files with only "00" Bytes on your device until the device is full. It would help in the most cases to secure delete enought for ever.
Even that may not be sufficient. The flash cards have some extra cells in spare, and so your earlier data may have been rolled out and your 00 bytes go to other cells.

If you want to securely delete the content of the flash card: Just destroy the card completely.
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#7
If you're so worried about passwords, why store them in the first place?
 
Posts: 543 | Thanked: 181 times | Joined on Aug 2009 @ Universe,LocalCluster.MilkyWay.Sol.Earth.Europe.Slovenia.Ljubljana
#8
Use encrypted storage for them from the start.. a simple gpg encrypted text file works great
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A quick list of what I have in the repos
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#9
Originally Posted by TA-t3 View Post
Even that may not be sufficient. The flash cards have some extra cells in spare, and so your earlier data may have been rolled out and your 00 bytes go to other cells.
Yes, not the best method. And I know about the problem. But it is better than nothing.
And compare, how many bytes are images, mp3 or videos and how many bytes are your sensitive password files?

Originally Posted by TA-t3 View Post
If you want to securely delete the content of the flash card: Just destroy the card completely.
I'm not sure, but I guess this could cause a problem with the warranty when you destroy the internal flash before you send the Device back to Nokia.
 
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#10
As a note, you can use a program like shred on a Linux desktop on the MMC device that the N8x0/N900 exports over USB (when it's unmounted), but as mentioned, that probably won't be terribly effective with flash memory. If you can't think of anything else, then you can always try it, but don't rely on it. Also be aware that if you're using a journalled file system on the card, it's usually a moot point anyhow.
 

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