Adding shred to Nautilus

[zaphodbblx]

found this neat shred utility here:
http://www.ubuntugeek.com/tag/shred-ubuntu
it uses Nautilus and you can shred a file with a right click
this is the info it tells you to input:

Label: Shred
Tooltip: shred utility to securely erase files
Icon: gtk-dialog-warning
Path: shred
Parameters: -f -u -v -z %M

what do the parameters mean?
how secure is the shred utility that is built into ubuntu?
I like to understand what I'm doing to my computer and how its being done and face it security often gets overlooked

[kestrel1]

If you type
shred --help
in a terminal it tells you what the parameters mean.

[zaphodbblx]

If you type
shred --help
in a terminal it tells you what the parameters mean.

thanks! I was a bit scared to type shred into the terminal

[HermanAB]

Just remember that shred doesn't really work. It isn't really any better than rm.

Cheers,

Herman

[hyper_ch]

Just remember that shred doesn't really work. It isn't really any better than rm.

because of the beauty of journaling filesystems.

[kestrel1]

because of the beauty of journaling filesystems.
For anyone interested a little more info o the above: http://en.wikipedia.org/wiki/Journaling_file_system

[cdenley]

Except by default, the actual file is not journaled, so overwriting with random data multiple times on a default configuration would protect it from being recovered by physically analyzing the disk platters with special tools.



man shred



In the case of ext3 file systems, the above disclaimer applies (and shred is thus of limited effectiveness) only in data=journal mode, which journals file data in addition to just metadata. In both the data=ordered (default) and data=writeback modes, shred works as usual. Ext3 journaling modes can be changed by adding the data=something option to the mount options for a particular file system in the /etc/fstab file, as documented in the mount man page (man mount).

[hyper_ch]

you don't know for sure what state the file is in.

[HermanAB]

The problem is the uncertainty.

Assuming you are not an exhibitionist - If you had a personal cloaking device that worked some of the time, would you walk around naked in public?

If you are going through a divorce and you had a paper shredder that sometimes shredded your bank statements and sometimes not, would you hand your office trash to your spouse's lawyer?

So, since shred cannot be relied upon, there is no point in using it. If you need control over your data, encrypt it with LUKS. Then you will have certainty.

Cheers,

Herman

[cdenley]

I am certain that my system mounts ext3 filesystem in ordered write mode. If I had files which already exist, and I wanted to erase the files securely without destroying the entire filesystem, I would certainly use shred or another similar utility. Of course encryption is a better method of protecting data, but if the data is already written without encryption, saying tools like shred are completely useless is absurd.

Even IF shred is "unreliable" on ext3 with ordered write mode, as you claim, it is still better than doing nothing.

[HermanAB]

Well, if you can entrust your deleted data to an unreliable tool, then you need to wonder whether you needed that tool in the first place.

That is why I am saying that shred is no better than rm. In fact, rm is better, since it doesn't leave you with a false sense of security.

If you are worried about data security, use LUKS. If not, don't bother.

Cheers,

Herman

[cdenley]

That is why I am saying that shred is no better than rm. In fact, rm is better, since it doesn't leave you with a false sense of security.

Well I certainly disagree. Using shred would prevent me from recovering your data. The rm command wouldn't.

[hyper_ch]

if shred would delete the actual data in question... which is to be disputed.

[cdenley]

if shred would delete the actual data in question... which is to be disputed.

Show me something which contradicts shred's documentation and indicates the actual data wouldn't be deleted when the default mount options for ext3 are used.

[kestrel1]

Would wipe be any better than shred?

sudo apt-get install wipe

[cdenley]

Would wipe be any better than shred?

sudo apt-get install wipe

I'm sure that uses the same method of simply overwriting a file.

[HermanAB]

Format a new file system (on a large USB memory stick for example):
mkfs.ext3 /dev/sdb
mkdir /mnt/test
mount /dev/sdb /mnt/test

Save some large text files.
cp -r ~/Documents /mnt/test
Run shred on all the files.

Dump the file system using dd and look for strings:
dd if=/dev/sdb | strings

Cheers,

Herman

[cdenley]

mkdir shred
dd if=/dev/zero of=shred.ext3 bs=1024 count=40960
mkfs.ext3 -F shred.ext3
sudo mount shred.ext3 ./shred -o loop
sudo chown $USER shred
for ((i=0;i<1000000;i+=1)); do echo this is a large text file;done>shred/test.txt
shred -n 1 -z -u shred/test.txt
sudo umount ./shred
strings shred.ext3

No strings were found from the file itself. The file's name was found, probably because the meta-data was journaled, but not the actual data. The same thing could have been accomplished by simply zeroing out the file.

[hyper_ch]

Show me something which contradicts shred's documentation and indicates the actual data wouldn't be deleted when the default mount options for ext3 are used.

did you test that it really does delete that data? what are the default mount options?

[cdenley]

did you test that it really does delete that data? what are the default mount options?

I just posted every command I used which shows that not a single byte was recoverable from the filesystem. For default mount options, try


man mount

Specifically, the relevant default mount option is data=ordered.