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Why 'rm -R star' Isn't Enough
zdburke writes: "Short but interesting article in the New York Times (free reg req'd) about how difficult it is to cover your digital tracks because electronic documents are so well distributed -- on your lap top, on your workstation, on the server... Yes there are tools to thoroughly delete files on your computer, rather than just unlinking them when they're put in the trash, but it's the distributed nature of content these days that poses a special problem to the Ollie North's of the world."
On my harddrive space challenged machine, usually the reason I delete something is to make room for something else. So, chances are if they want "super-secret-MS-secrets.txt", the sectors have already been overwritten by "bspears-nude.jpg"
:)
If you're afraid that mirrors will copy your files, why don't you just overwrite the file with the same name, just some bogus data. That file will be mirrored again since it has a new date.
Sometimes when a problem gets high tech, it's time for a low-tech approach.
Wealth is the product of man's capacity to think. -Ayn Rand
It's quite possible to recover files, because, much like PCs nothing actually gets 'deleted'. The inode is marked as 'available for reuse' and removed from the directory entry, but doesn't actually remove anything. /dev/zero over a file just prior to erasing it work?)
Looking for an undelete? Take a look at the coroners toolkit. There's even instructions on how to recover files from a unix partition (any unix). It's one of those ones which you'd _really_ need to recover the data because it's hard work and a pain, but it is possible.
I don't recall seeing and 'write with zeros' program for Unix. I guess there must be some out there, since at a guess it's fairly trivial. (would dding
Of course, there's always disk analysis with an electron microscope, which I've always heard was possible but it's not one I've ever had substantiated.
Don't try to cover your tracks, delete every little bit of info about you, that's waaay too much time and effort. Want you want to do is put sooo much crap out there, no one can tell the real info from the synthetic.
Also, it's the internet. Make up shit. The only thing you really can't lie about is online purchases with a credit card (well...), anything else is open territory for your imagination!
Say you have important information on your hard drive. You only want one other person to see that information so you put that information on a floppy disk then give it to that person. No one else can see this information. You then take a pencil and stab the magnetic film of the floppy about 30 - 40 times. You then take lighter fluid and douse the entire floppy and light it. Stomp on the ashes for extra measure. Since the data has been on your computer. You must first take your hard drive out. Expose it to a giant magnet, then shoot it with a 12 guage (twice). Take all the IC's out of your computer and smash them with a sledgehammer, then run over them with your truck. Burn those with lighter fluid too. Since your monitor most likely displayed that sensitive information, you must take it to a helicopter and drop it. Have the helicopter land on the debris for safe measure.
Ensure that the other person gives your data to no one. Do a thorough background check on him and his closest 50 living relatives. After he is done processing the information; shoot him.
No need to worry about any information getting anywhere.
That is because modern computers organize information by using file-system directories that point to physical areas on a disk drive where the data resides. "Deleting" the information usually only breaks the link between the directory and the data so that the original storage space can be reused in the future.
:)
Gee...what a stride. Too bad we didn't have technology like this in the 80's. A company like Norton could have made a killing making tools to relink the file table with these sectors, almost as if they were UNDELETEing the file.
I just love expressions like "modern computers" used in this way, when the reporter meant to say "Well...this is new to me, must be new to the computer too." Of course, we all know that it is the computer that has this behaviour - not the OS sitting on top of it
IIRC, DOS used to just replace the first character name of a file with a ? in the FAT when you deleted it, so to undelete it, you just supplied a letter to "rename" the file as.
I personally don't keep anything around on my computer that has any incriminating information. If I did, I'd be damn sure that it's not in a shared space that gets copied onto any server or anything like that. I think any computer savy person already knows that you just don't keep digital records of things you don't want people to find out, and you definitely don't keep them anywhere there's a remote possibility the data could be duplicated. This will probably only jump up and bite the illiterate "business major" types, and I really don't have a problem with that.
~ now you know
If you are concerned enough about your data to want to permanently delete it, or at least keep your tracks covered, you'll use PGP and either wipe your freespace multiple times to completely obscure data, and/or keep your important files encrypted.
Although encryption is, in theory, breakable, the resources to do so don't exist (unless the NSA has some quantum computers squirreled away somewhere), your files will be safe.
In short, if you want to keep files private, use PGP, and use it wisely. If you don't make more of an attempt, other than "well, if I tell Windows to delete it, it's gone", to keep files hidden/gone for good, you deserve to have your data recovered.
Gawyn
Freedom of Speech?
A big 'old electromagnet.
Degauss the disk and it's gone for good.
Accually, does anyone else remember the movie Blue Thunder?
The video tape jackets had electromagnets build into them, and thus could delete any tape that the bad guys wanted.[1]
I wonder when IBM or someone will build a HD with a self delete 'fail safe' system. When the drive powers down without a password, wipe.
[1] There is some ironny here somewhere folks. Just can't think of a witty remark.
III.IIVIVIXIIVIVIIIVVIIIIXVIIIXIIIIIIIIVIIIIVVIII
It is possible to take a disk apart and use an electron microscope to read information from the individual magnetic spots on the surface of a disk that may have been intentionally erased, Mr. Patzakis said.
I monitor the forensics list on securityfocus, and there was discussion that this might be mostly a myth.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
Yes there are tools to thoroughly delete files on your computer, rather than just unlinking them when they're put in the trash, but it's the distributed nature of content these days that poses a special problem to the Ollie North's of the world.
:D
Well, I don't think any OS has ever been short of undeletion tools - in unix, one can grep the inodes on a disk for a particular known string of a file and recover it fron a known template. Tools like gpart (a partition guesser) also easily recover those vital 512 bytes of your hard disk.
Where Unix has been lacking, behind most other systems, is the opposite - a good, reliable, trashcan. It might be interesting to note that there's now a reliable trashcan for Linux, BSD and other glibc systems th simply preloads and wraps unlink, `move and a couple of other system calls.
Since glibc is a part of the Linux Standard base, it works along with every LSB standard app. Even better, it doesn't matter whether you delete the file from KDE, GNOME, shittyunixtoolkitforhellcirca1980something or a terminal.
Anyway, check out Libtrash. And if you're a GNOME or KDE hacker, I'll give you a big hug if you use this as the default trashcan or your next release.
Of course `rm -R *` isn't enough -- it just unlinks files, but doesn't delete datablocks. To delete datablocks, try the -P option which overwrites the file data before unlinking. Unfortunately, this option is not available on GNU `rm` which is used on most Linux systems.
PGP is a brillient tool for encryption (esp. e-mail) and PGP disk or Scramdisk are great for secure archiving on windoze machines. However the PGP wipe isn't very good. This link explains why and gives good alterantives for windoze users.
Linux users already have encrypted filesystems and secure file wipeing as standard in all(?) common distro's. (I know that SuSE even lets you overwite the wiped files with zeros to hide its very existance)
Anyone quoted by a reporter knows how little they understand
Don't believe what you read is the truth.
There is a program called shred that comes with most distributions nowadays that overwrites the files with different patterns before unlinking them. There was something about this on Slashdot a while ago. This program seems to use a simular algorithm.
I was hired to recover files from a hard drive by a woman who was getting a divorce. Her husband had been cheeting on her. The moron had norton systemworks installed on his system and never defraged his drive. I was able to recover over a years worth of incriminating emails with nortons undelete. Boy was that easy money
http://Lenny.com
4 great justice!
If you have problems destroying documents, you could always ask Arthur Anderson or Enron.
Bit busy -- finishing up The Book(TM) -- but I wrote a bit about this subject some time ago. Head over to: http://www.doxpara.com/read.php/security/secure_de letion.html
There's a Part 2, and some other stuff over there too. yeah, the site needs to be updated desperately. Wait till feb.
There's one piece of information that's very new and very, very cool: Apparently, some company has been going around the WTC crash site, picking out hard drives from crushed servers, and (though I can't imagine this) actually recovering data from the drives through all the crush damage and dust. I mean, yes, the concept that a non-portable, super expensive, very labor intensive read head would be able to recover significantly more data redundancy than some mass produced mag-head is unsurprising, but...damn.
--Dan
The US government today announced plans to impose restrictions on so called 'File Deletion' utilities, and possibly even outlaw them altogether, in the name of national security. "These file deletion programs can be used by terrorists to cover their tracks, and remove evidence." claimed a government security expert. "criminals such as Osama Bin Laden, can cover up any electronic evidence, and make prosecution impossible." However, civil liberties groups claim that the ban would infringe their first amendment rights. Other experts claim that anyone can create a file deletion program with even basic programming knowledge. We interviewed one expert who explained how: "One simple way to make sure your data is wiped clean, is remove the hard drive from your computer, and place it in a furnace for 15-20 minutes." the interview was cut short, when government agents stormed the building and arrested the expert for "discussing circumnavigation devices for data deletion".
This comment does not represent the views or opinions of the user.
I ask this since there are unerase utils in windows, could they be using a vfs? If they are, wouldn't they have to stay resident forever monitoring all content?
DOS 6.x had an undelete.exe TSR that patched the DOS call to remove a file. It had two modes: Delete Tracker (remember deleted directory entries) and the stronger Delete Sentry (similar to the Mac's trash can and to the forthcoming Windows 9x's recycle bin). When using the Delete Tracker or non-TSR mode, it would look at the directory entry of the deleted file (from the directory in non-TSR or from a database in Delete Tracker) and then follow the FAT chain to retrieve as much of the file as it could. Delete Sentry simply moved files into a folder C:\SENTRY, no matter what program deleted them, ignoring *.tmp and a few other file types.
Mac OS 7 or later and Windows 4 or later, on the other hand, have two separate delete calls (for discussion, call them unlink() and ShellDelete()). The unlink() call actually deletes a file and should be used on tmp files, in uninstallers, etc. ShellDelete(), on the other hand, moves a file to a folder called vol:Trash (on Mac) or vol:\Recycled (on Windows); the shell (Finder or Explorer) provides a command Empty Trash... to do what is essentially an rm -rf on the Trash folder.
In UNIX systems and their clones, merely make a shell command alias that maps a command to move the file to the ~/.trash folder.
Will I retire or break 10K?
Presumably PGP runs on unix?
PGP 6.5.8, the last freeware version
GnuPG 1.0.6, the GNU Privacy Guard, is a free implementation of the OpenPGP spec.
Will I retire or break 10K?
On some systems, rm has an option to nuke the contents of the file before unlinking it:
man rm
<snip>
-P Overwrite regular files before deleting them. Files are overwritten
three times, first with the byte pattern 0xff, then 0x00, and then 0xff
again, before they are deleted.
</snip>
You can just put "alias rm rm -P" in your login script to make this the default.
Considering most systems come with 15-60gig drives now, it would take a long time to actually write over all the sectors used for that file in its entire lifetime.
No longer than a couple defrags. Simply open thousands of multimegabyte files, and then in each file, write a layer of 0's, a layer of 1's, and a couple layers of random data, and you're pretty safe. Five passes on a 20 GB partition shouldn't take more than a few hours depending on the transfer rate from computer to drive.
Will I retire or break 10K?
The man page for shred says
CAUTION: Note that shred relies on a very important assumption: that the filesystem
overwrites data in place. This is the traditional way to do things, but many mod
ern filesystem designs do not satisfy this assumption. The following are examples
of filesystems on which shred is not effective:
* log-structured or journaled filesystems, such as those supplied with
AIX and Solaris (and JFS, ReiserFS, XFS, etc.)
Using shred on ext3 does not seem to be a good idea. I use srm instead. srm overwrites the data 30+ different times using bit patterns and random patterns. The high number of overwrites is supposed not only to allow for slight deviations in alignment betweeen the drive heads and track on the platter, but also meets some very high (you might say "federal") standards, short of (or in some cases, followed by) incinerating the disk.
To-do List: Receive telemarketing call during a tornado warning. Check.
There are a few other caveats, but that's the important one for me, given that I upgraded my machine at the weekend and only yesterday reinstalled Mandrake 8.1 with reiserfs for both my / and
Cheers,
Tim
It's official. Most of you are morons.
From the GNU shred info node:
shred overwrites devices or files, to help prevent even very expensive hardware from recovering the data.
Ordinarily when you remove a file (*note rm invocation::), the data is not actually destroyed. Only the index listing where the file is stored is destroyed, and the storage is made available for reuse. There are undelete utilities that will attempt to reconstruct the index and can bring the file back if the parts were not reused.
GNU shred is very featerful, as costumary in GNU utils, and has many flags to modify the behaviour.
BSD ppl are always praising the 'Unix Way' of small utilities that do a very defined job and nothing more, and hate the extended features that GNU utils provide; in this case it's BSD rm that is doing something that could be done by another tool by adding a flag! Horror!
Seriously, GNU shred is a good tool, and it can receive some interesting flags that a simple rm -P doesn't support.
cheers,
fsmunoz
Apparently, this isn't 100% effective:
Contrary to conventional wisdom, "volatile" semiconductor memory does not entirely lose its contents when power is removed. Both static (SRAM) and dynamic (DRAM) memory retains some information on the data stored in it while power was still applied. SRAM is particularly susceptible to this problem, as storing the same data in it over a long period of time has the effect of altering the preferred power-up state to the state which was stored when power was removed. Older SRAM chips could often "remember" the previously held state for several days. In fact, it is possible to manufacture SRAM's which always have a certain state on power-up, but which can be overwritten later on - a kind of "writeable ROM".
This is from Peter Gutmann's paper Secure Deletion of Data from Magnetic and Solid-State Memory
While the resources probably don't exist to directly attack PGP, this makes certain assumptions
Even if those are true, there are other attacks possible - Most people don't use a sufficient passphrase, so that becomes the easiest attack.
After that, you have to worry about things like "Magic Lantern" and black bag jobs
How paranoid do you want to get?
-- 73 de KG2V For the Children - RKBA! "You are what you do when it counts" - the Masso
For most of us here, the gov'ts electron-microscope method of determining old data is irrelevant. How many of you here think that it'll be employed against you? That said, I suppose for those of us who engage in a big-time trading of files via P2P networks, & DeCSS, etc, there's always the possibility of criminal prosecutions. So, let me go over the 3 types of "data deletion", and say where each should be used:
1. Typical deletion. Files are unlinked with their directories, so your OS does not "see" them and has more space available to write with. If the information is not sensitive, or you don't fear intrusion, this is the fastest, and also best, method of deletion. It simply changes the first character of a file name do something that your OS doesn't recognize -- a very fast process. The Advantage: data is recoverable via a data-recovery utility. The Disadvantage: the data has not been securely eliminated.
2. Simple once-sweep wipe-over deletion. Either random 1s and 0s, or wholly 1s, or wholly 0s, are written over an entire file. Use this for data that is sensitive, or where you fear cyber-intrusion by hackers. The Advantage: data is securely eliminated, beyond the reach of anyone who hacks into your computer. The Disadvantage: data is irrecoverable to you, should you realize you made a mistake, and this process is slower.
3. A multi-sweep wipe. Same as above, but many sweeps are performed, enough to make typical electron-microscopy methods of data-recovery inviable. This method effectively makes data irrecoverable by any means. Electron microscopes can detect "old zeros" by ghost-patterns, a slight trace. But if data has been written over many times, the older data is impossible to recover even by those methods. The Advantage: this method securely removes the data, beyond the reach of any technological means. The Disadvantage: this method is very slow, and again, data is irrecoverable should you learn you made a mistake.
It should be noted that whenever you want to securely delete data, not only do you need to wipe the file, but you also need to wipe your swap files and your temporary files.
So, let me summarize when each of the methods of "data-removal" should be used, starting with the strongest method (a multi-sweep wipe), and ending with the weakest method (the renaming of the first filename character to something unrecognizable):
1. A multi-sweep wipe. Use this when you have data on your computer that could be used against you in a lawsuit or prosecution. For example, certain kinds of pornography, copyrighted files, warez, and other various information that's been deemed "illegal" by the Information Police in the MPAA, RIAA, MS, and the US Gov't.
2. A single-sweep wipe. Use this for information that is sensitive, but that you need not fear should the government get ahold of. For exmaple, financial files, files containing credit-card information, etc -- anything you'd want to protect from online-hackers using data-recovery programs. The government, though draconian, has not been known to steal people's credit cards using electron-microscopy. Similarly, hackers have not the resources to use electron-microscopy to acquire your credit cards -- nor would it be worth it. However, if your a high-tech company selling your computer equipment to another company, a multi-sweep delete of your files may be necessary to protect your information from competing companies, who may have bought your machinery through another company as a front.
3. A deletion that dissociates the file from the directory (renames the 1st character). Use this for non-sensitive data. For example, stories you've written, calendars, lists, ideas, old programs, pictures, etc etc.
Hope this has been helpful -- and please, remember, if you want to securely remove sensitive data either by a single-sweep wipe (to protect it from hackers) or a multi-sweep wipe (to protect it from the government), please remember to also securely remove swap files and temporary files as well!
social sciences can never use experience to verify their statemen
FreeBSD users have the program obliterate in the sysutils part of the ports collection. It takes pains to overwrite the data in order to make sure the file, even if re-linked, is unusable.
/dev/rand.
If I understand correctly, it open the file for writing multiple times first. First it writes 0s, then 1s, then alternate beginning 0s and 1s, then 1s and 0s, then patterns of 1s and 0s of all descriptions, then several passes from
The upshot is that even if you find the inode and relink to the data, it's been overwritten so many times than you really can't possibly recover it even using forensic methods.
Was it the orange stains on his hands and the faint odor of cheese that gave him away?
I find the following command useful:
/dev/hda, you don't mind reinstalling everything. It's sort of an OS suicide command.
# dd if=/dev/random of=/dev/hda
This is assuming, of course, that if your root partition is on
Using random data as opposed to zeroes is more secure because writing zeroes may leave a readable residual magnetic signature on the media whereas random data tends to obscure the mag sig.
Give me my freedom, and I'll take care of my own security, thank you.
> Then again, I don't have anything that important anyways.
Don't be so certain of that. Open up your wallet, and you'll see much of importance. No credit cards? That's not the most important thing you have. Take a close look at your driver's license, or any ID you have. That's of great value to many people, and whether or not you trust it to a computer most state governments will. Leaving something as simple as your name in a computer proves that a person by your name exists, which can be used for profit or to complete an agenda.
Virg
This recovery is a breeze. Just follow these easy steps.
1.) Take the HD out of your machine, take it to your clean room, and crack it open.
2.) Pull the platters, one by one, run them under your magnetometer, and use the programming in your magnetometer to develop a magnetic wave map of your drive. Store this image in your workstation.
3.) Run the analyser over the waveform to get a datamap of the drive. Be sure to save the layers as separate images.
4.) Pan back through the resulting images, and find the one that corresponds to the drive topology at the time you want (the time when the file/data still existed in readable format).
5.) Create a disk image file from that waveform.
6.) Mount the resulting image, and copy your file to a more secure location.
See? Quick and easy.
Virg
Continually write cruft to hard drive: Run a batch script that continually loops through: 1) dd from /dev/zero to a dummy file on partition; 2) delete when drive fills; 3) dd from dev/urandom to same file; delete file. As the drive will have many writes to it, it would make things very tough to recover. This never had much performance impact on the machine.
I wish I could find a utility that cleans out inode information, much like the dos/win utils that scrub deleted filenames from the FAT.
Edit documents and browse web from a virtual machine on an encrypted device:
I use the loopback patches (/pub/linux/kernel/people/hvr at your local kernel mirror) to run an encrypted device. I then use VMWare (though bochs, plex86, or User Mode Linux should work) to run Linux and Windows for browsing and email writing. Note that VMWare has a nice "undoable" disk feature, in which you can "commit" or "discard" changes to the virtual disk. So I have a pristine Win95 VM, which I log into to do my stuff, and then I discard the changes, thereby removing cached macterial, cookies, etc.
Note that this doesn't thwart traffic analysis or "rubber hose" tactics. In fact, once the loopback devices are mounted, you can perform standard file/data recovery techniques on them.
Use file encryption for email and sensitive files. I use GnuPG for this.
Method of processing duck feet
I'm surprised I've seen no discussion here of the very basic problem of file slack space - that unallocated space at the end of the last sector of every data file, except those that exactly fill a disk sector. Most of the methods described here for easy ways to wipe empty hard drive space do not overwrite all the file slack space. You need a program that does that explicitly. Otherwise every sector with the tail end of a file contains easily recoverable data, although disassociated from any filename. Given that the slack space on a hard drive averages out to $sectorsize*$numfiles/2 (on average, 1/2 of a sector, times the number of files), the average 40Gb hard drive with 10,000 files might have 50Mb or more of recoverable data, even if the "empty" space were completely and unrecoverably wiped.
I learned about this while preparing to publish a program commercially, and discovered that (at least at the time) files I copied to the distribution media master sometimes contained sensitive data, such as the source code, from my own hard drive. Basically, DOS wasn't very picky about copying a few extra bytes along with the actual file length, as long as the extra bytes didn't go past the end of the destination sector. The answer? I used a slack wiping program on the master disk before sending it for duplication.
--Brandon / Split Infinity Music
dd if=/dev/zero of=/dev/hda works for me ;)
Repeate 4 or 5 times, and good luch recovering anything...
LedgerSMB: Open source Accounting/ERP
'rm -Rf star' is much preferrable, or '/bin/yes | rm -R star'. Otherwise you would be there all day pressing 'y'. You could always do it the Homer Simspon water bird way...
... offtopic and frivilous...)
(I know
That's because they knew how. Murder was part of it.
DMCA, Hollings, Palladium. What might have sounded like paranoia is now common sense.