Re: Linux FS Question
On Wed, 18 Jun 1997, Rick Macdonald wrote: > > Actually it's not superstition at all. I think you can still recover a file > > that's been overwritten once with zeroes... just open the HD (in a clean > > room, of course) and read off the sectors with a electron microscope (or > > I think the older Norton manuals explained the "government wipe" in > greater detail. The one I have now doesn't say how many repeats, only that > a fast wipe of one pass of zeros takes a few seconds on a 1.44MB floppy, > whereas a government wipe takes about two hours. It says the "last > character" used has to be decimal 246. I wonder if there are government > employees who make a living scraping ones and zeros off erased disks... There's a hardware aspect to the problem of erasing floppies by writing over them. Whereas a HD is written by the same head every time, floppies are typicaly written by several different ones, which may vary in their exact geometry. You might write over it many times, but someone just reads the data from the guard bands. Surely the residual value of a used floppy is less than two hours usage of any piece of hardware. Perhaps two seconds in a mincing machine. -- David Wright, Open University, Earth Science Department, Milton Keynes MK7 6AA U.K. email: [EMAIL PROTECTED] tel: +44 1908 653 739 fax: +44 1908 655 151 -- TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to [EMAIL PROTECTED] . Trouble? e-mail to [EMAIL PROTECTED] .
Re: Linux FS Question
On Wed, 18 Jun 1997, Christian Hudon wrote: > On Jun 18, Rick Macdonald wrote > > > > Well, you could overwrite the file with gibberish _before_ deleting it. > > I think that's what Norton does, several times if I remember correctly. > > That's to comply with US federal regs, which seem a bit superstitious to > > me! Actually, the giberrish itself is probably some specified bit pattern. > > Actually it's not superstition at all. I think you can still recover a file > that's been overwritten once with zeroes... just open the HD (in a clean > room, of course) and read off the sectors with a electron microscope (or > something like that). The voltage levels will all be bellow the 'zero > threshold' but they won't be all equal, and from the small variations you > can recover the contents of the file before it was overwritten with > zeroes. Of course, whatever was written on your hard drive must be worth > quite a bit of cash (to you or to other people) for this recovery method to > make sense economically. So the 'overwrite multiple times' precaution is > probably overkill for the vast majority of people. I used to recover some badly trashed floppys under M$DO$ with Central Point Software PCFormat (CPS has been absorbed by Symantic/Norton). Somehow it could read and rewrite every byte on the disk. Saved some peoples hyde down at the old rubber factory. That tells me that it may be quite possible to read an overwritten disk. But multiple overwrites with varying patterns should make that impossible. http://www.sound.net/~wpmills/ - : W. Paul Mills : Bill, I was there several years ago. : : Topeka, Kansas, U.S.A. : Why would I want to go back tomorrow?: : [EMAIL PROTECTED] : Where were you! : : [EMAIL PROTECTED] : : : [EMAIL PROTECTED] : Linux: Tomorrow's operating system, : : [EMAIL PROTECTED] :here, today. : : [EMAIL PROTECTED] : : : compuserve 70023,1750 : #define MY_TRUE_LOVE computer: -- http://homepage.midusa.net/~wpmills/ - -- TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to [EMAIL PROTECTED] . Trouble? e-mail to [EMAIL PROTECTED] .
Re: Linux FS Question
Christian writes: > I think you can still recover a file that's been overwritten once with > zeroes... just open the HD (in a clean room, of course) and read off the > sectors with a electron microscope (or something like that). No need to open the drive. Just signal process the analog output from the head. John Hasler [EMAIL PROTECTED] (John Hasler) Dancing Horse Hill Elmwood, WI -- TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to [EMAIL PROTECTED] . Trouble? e-mail to [EMAIL PROTECTED] .
Re: Linux FS Question
On Wed, 18 Jun 1997, Christian Hudon wrote: > On Jun 18, Rick Macdonald wrote > > > > Well, you could overwrite the file with gibberish _before_ deleting it. > > I think that's what Norton does, several times if I remember correctly. > > That's to comply with US federal regs, which seem a bit superstitious to > > me! Actually, the giberrish itself is probably some specified bit pattern. > > Actually it's not superstition at all. I think you can still recover a file > that's been overwritten once with zeroes... just open the HD (in a clean > room, of course) and read off the sectors with a electron microscope (or I think the older Norton manuals explained the "government wipe" in greater detail. The one I have now doesn't say how many repeats, only that a fast wipe of one pass of zeros takes a few seconds on a 1.44MB floppy, whereas a government wipe takes about two hours. It says the "last character" used has to be decimal 246. I wonder if there are government employees who make a living scraping ones and zeros off erased disks... Anyway, I think the asker of the question got his answer, and I need to break out a dictionary next time I go to write the word "gibberish"! ...RickM... -- TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to [EMAIL PROTECTED] . Trouble? e-mail to [EMAIL PROTECTED] .
Re: Linux FS Question
On Jun 18, Rick Macdonald wrote > > Well, you could overwrite the file with gibberish _before_ deleting it. > I think that's what Norton does, several times if I remember correctly. > That's to comply with US federal regs, which seem a bit superstitious to > me! Actually, the giberrish itself is probably some specified bit pattern. Actually it's not superstition at all. I think you can still recover a file that's been overwritten once with zeroes... just open the HD (in a clean room, of course) and read off the sectors with a electron microscope (or something like that). The voltage levels will all be bellow the 'zero threshold' but they won't be all equal, and from the small variations you can recover the contents of the file before it was overwritten with zeroes. Of course, whatever was written on your hard drive must be worth quite a bit of cash (to you or to other people) for this recovery method to make sense economically. So the 'overwrite multiple times' precaution is probably overkill for the vast majority of people. Christian pgp4weHG5n9wM.pgp Description: PGP signature
Re: Linux FS Question
On Wed, 18 Jun 1997 [EMAIL PROTECTED] wrote: > > Date: Wed, 18 Jun 1997 09:01:23 -0500 > > To:debian-user@lists.debian.org > > From: "Tim O'Brien" <[EMAIL PROTECTED]> > > Subject: Re: Linux FS Question > > > Is there a way to securely delete a file? Or do I need to study the e2fs > > and develop a program to do it? I'm sure there's lots of people out there > > who'd like the ability to know that when something's been deleted, it's > > gone; no line, no waiting.. Right now. > > > > Ideas? > > > > You could write a small c prog, that stats the file to get the size, > then open the file, write 0's to the whole file, close it and unlink. > Most of this is standard library calls. > > Stephen. One example of a program to do this is can be found on sunsite.unc.edu in /pub/Linux/utils/file/wipe.tgz Also note that the chattr(1) program claims to set a file attribute that will cause a file to be overwritten with zeros before it is deleted from an ext2 file system. This will not work because the required code was removed from the Linux kernel in version 1.3.36 (Oct 95) and has not been added back. See the following comment from /usr/src/linux/fs/ext2/truncate.c: /* * Secure deletion currently doesn't work. It interacts very badly * with buffers shared with memory mappings, and for that reason * can't be done in the truncate() routines. It should instead be * done separately in "release()" before calling the truncate routines * that will release the actual file blocks. * * Linus */ Anyone looking for a kernel hacking project? John Kuhn [EMAIL PROTECTED] -- TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to [EMAIL PROTECTED] . Trouble? e-mail to [EMAIL PROTECTED] .
Re: Linux FS Question
Maybe a proper way of doing is to fill the file with zeroes from /dev/zero before removing. Regards, Andree -- | Institute of Geophysics phone: +49 40 4123 4389 ANDREE LEIDENFROST | University of Hamburg fax: +49 40 4123 5441 Geophysicist | Bundesstrasse 55 e-mail: [EMAIL PROTECTED] | D-20146 Hamburgwww: www.app-geoph.dkrz.de -- TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to [EMAIL PROTECTED] . Trouble? e-mail to [EMAIL PROTECTED] .
Re: Linux FS Question
> Date: Wed, 18 Jun 1997 09:01:23 -0500 > To:debian-user@lists.debian.org > From: "Tim O'Brien" <[EMAIL PROTECTED]> > Subject: Re: Linux FS Question > Is there a way to securely delete a file? Or do I need to study the e2fs > and develop a program to do it? I'm sure there's lots of people out there > who'd like the ability to know that when something's been deleted, it's > gone; no line, no waiting.. Right now. > > Ideas? > You could write a small c prog, that stats the file to get the size, then open the file, write 0's to the whole file, close it and unlink. Most of this is standard library calls. Stephen. -- TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to [EMAIL PROTECTED] . Trouble? e-mail to [EMAIL PROTECTED] .
Re: Linux FS Question
On Wed, 18 Jun 1997, Tim O'Brien wrote: > Is there a way to securely delete a file? Or do I need to study the e2fs > and develop a program to do it? I'm sure there's lots of people out there > who'd like the ability to know that when something's been deleted, it's > gone; no line, no waiting.. Right now. Kinda like a Norton wipedisk? > Ideas? Well, you could overwrite the file with gibberish _before_ deleting it. I think that's what Norton does, several times if I remember correctly. That's to comply with US federal regs, which seem a bit superstitious to me! Actually, the giberrish itself is probably some specified bit pattern. ...RickM... -- TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to [EMAIL PROTECTED] . Trouble? e-mail to [EMAIL PROTECTED] .
Re: Linux FS Question
At 11:19 AM 6/18/97 +0200, you wrote: >Hi Tim, > >as far as I know the data is still there (until the blocks that it >occupies are reused). Unfortunately deleting for ext2fs meaning deleting >the last reference or pointer to the file. Consequently the file simply Is there a way to securely delete a file? Or do I need to study the e2fs and develop a program to do it? I'm sure there's lots of people out there who'd like the ability to know that when something's been deleted, it's gone; no line, no waiting.. Right now. Ideas? Thanks, Tim Linux 2.0.6 i486 Because reboots are for upgrades! ---> [EMAIL PROTECTED] <-- -- TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to [EMAIL PROTECTED] . Trouble? e-mail to [EMAIL PROTECTED] .
Re: Linux FS Question
On Jun 17, Tim O'Brien wrote > Under the FAT16 system when a file is deleted, it's only removed from the > FAT. Though the file appears gone, it still remains on the drive. > > When something is removed on a Linux box using the rm command, is the file > gone for good or is it just removed from view while it remains on the disk? > AFAIK it's really gone at least shortly afterwards because the space will be reused. Greetings, Christian -- Christian Meder, email: [EMAIL PROTECTED] What's the railroad to me ? I never go to see Where it ends. It fills a few hollows, And makes banks for the swallows, It sets the sand a-blowing, And the blackberries a-growing. (Henry David Thoreau) -- TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to [EMAIL PROTECTED] . Trouble? e-mail to [EMAIL PROTECTED] .
Re: Linux FS Question
On Tue, 17 Jun 1997, Tim O'Brien wrote: > When something is removed on a Linux box using the rm command, is the file > gone for good or is it just removed from view while it remains on the disk? Nope. It's pretty much gone forever. Will [EMAIL PROTECTED] [EMAIL PROTECTED] http://www.ecl.udel.edu/~lowe/ A thought: this message has been brought to you by the number -7, the letter ê and the many, many, people who spent years and lifetimes and stuff and lotsa money to invent email. So I guess we could thank Ben Franklin, 'cause without electricity, we couldn't have ELECTRONIC mail. Of course, without the chinese guy who invented kites, ol' Ben couldn't a' done his stuff and wow, that guy who invented string -- TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to [EMAIL PROTECTED] . Trouble? e-mail to [EMAIL PROTECTED] .
